Highly Aligned Graphene Aerogels for Multifunctional Composites

Wu, Ying; An, Chao; Guo, Yaru; Zong, Yangyang; Jiang, Naisheng; Zheng, Qingbin; Yu, Zhong-Zhen

doi:10.1007/s40820-024-01357-w

Highly Aligned Graphene Aerogels for Multifunctional Composites

Review
Open access
Published: 15 February 2024

Volume 16, article number 118, (2024)
Cite this article

Download PDF

You have full access to this open access article

Nano-Micro Letters Aims and scope Submit manuscript

Highly Aligned Graphene Aerogels for Multifunctional Composites

Download PDF

Ying Wu^1,2,
Chao An^1,2,
Yaru Guo^1,2,
Yangyang Zong^1,2,
Naisheng Jiang^1,2,
Qingbin Zheng³ &
…
Zhong-Zhen Yu⁴

3881 Accesses
2 Citations
2 Altmetric
Explore all metrics

Highlights

Aligned graphene building blocks take full advantages of the outstanding properties of graphene.
Comprehensive review of recent advancements in the utilization of highly aligned graphene aerogels for multifunctional applications.
By systematically summarizing the controlled assembly, aligned structural attributes, quantitative characterization methods, anisotropic properties, and multifunctional applications of graphene aerogels, this review enhances understanding of the material's potential for diverse applications, offering tailored properties and novel functionalities.

Abstract

Stemming from the unique in-plane honeycomb lattice structure and the sp² hybridized carbon atoms bonded by exceptionally strong carbon–carbon bonds, graphene exhibits remarkable anisotropic electrical, mechanical, and thermal properties. To maximize the utilization of graphene's in-plane properties, pre-constructed and aligned structures, such as oriented aerogels, films, and fibers, have been designed. The unique combination of aligned structure, high surface area, excellent electrical conductivity, mechanical stability, thermal conductivity, and porous nature of highly aligned graphene aerogels allows for tailored and enhanced performance in specific directions, enabling advancements in diverse fields. This review provides a comprehensive overview of recent advances in highly aligned graphene aerogels and their composites. It highlights the fabrication methods of aligned graphene aerogels and the optimization of alignment which can be estimated both qualitatively and quantitatively. The oriented scaffolds endow graphene aerogels and their composites with anisotropic properties, showing enhanced electrical, mechanical, and thermal properties along the alignment at the sacrifice of the perpendicular direction. This review showcases remarkable properties and applications of aligned graphene aerogels and their composites, such as their suitability for electronics, environmental applications, thermal management, and energy storage. Challenges and potential opportunities are proposed to offer new insights into prospects of this material.

Aligned-graphene composites: a review

Article 01 October 2018

Graphene Nanoarchitectonics: Approaching the Excellent Properties of Graphene from Microscale to Macroscale

Article 02 September 2014

Aerogels based on carbon nanomaterials

Article 11 July 2016

Use our pre-submission checklist

Avoid common mistakes on your manuscript.

1 Introduction

Graphene aerogels have emerged as a highly promising class of materials due to their exceptional properties and diverse applications. Their lightweight and highly porous structures which are composed of interconnected graphene sheets exhibit remarkable mechanical [1], electrical [2], thermal [3], and photo-thermal [7,8,9]. Highly aligned graphene aerogels are characterized by the preferential orientation of individual graphene sheets [10], resulting in a high aspect ratio and a common directionality. This controlled alignment imparts several notable benefits over their randomly oriented counterparts. Firstly, the aligned structure of graphene aerogels significantly enhances their mechanical strength and stiffness, making them capable of withstanding higher loads and exhibiting remarkable structural integrity [11, 12]. This enhanced mechanical robustness is particularly advantageous for applications requiring materials with high strength-to-weight ratios, such as lightweight structural components, flexible electronics, and aerospace materials. Secondly, alignment greatly influences the electrical conductivity of graphene aerogels [13]. The ordered arrangement of graphene sheets allows for efficient charge transport pathways along the aligned direction, resulting in anisotropic electrical conductivity. This can be applied in electronic devices, such as field-effect transistors, where aligned graphene aerogels enable improved charge mobility and device performance. Moreover, the anisotropic conductivity of aligned graphene aerogels facilitates the development of directional electronic devices and sensors [14], opening up new avenues for electronic and sensing applications. Thirdly, alignment plays a vital role in facilitating efficient heat and mass transfer within graphene aerogels [15]. The highly ordered structure enables preferential pathways for thermal conduction, enabling rapid heat dissipation and effective thermal management. Furthermore, the aligned channels within the aerogel structure provide efficient transport pathways for gases and liquids, making aligned graphene aerogels suitable for applications such as thermal steam and organic absorption.

Significant progress has been made in the synthesis and characterization of highly aligned graphene aerogels. Researchers have employed various techniques, including directional freeze casting [4a) [70]. The resultant freeze-dried monolith exhibited well-aligned frameworks along the immersing direction (Fig. 4d) and cellular channel-like architectures in the cross-section view (Fig. 4e). The aligned graphene aerogels was achieved by immersing GO suspensions through a continuous injection into liquid nitrogen [55]. This inventive technique combined spinning technology with ice-templating alignment, facilitating the generation of aligned pore structures. By situating a container filled with a GO suspension atop a thermally conductive base and encompassing it with thermally insulating surroundings on a chilled platform, a unidirectional temperature gradient is generated, emanating from the bottom towards the top (as depicted in Fig. 4b). This thermal configuration prompts the vertical growth of ice crystals. Consequently, the resultant graphene aerogel exhibits vertically aligned graphene walls (Fig. 4f), alongside tubular structures displaying comparatively less alignment within the horizontal plane (Fig. 4g) [74, 83]. Affixing the mold to the side of a metallic box filled with liquid nitrogen generates a horizontal temperature gradient (Fig. 4c), fostering the lateral growth of ice crystals and corresponding alignment [84].

2.1.2 Bidirectional Freeze Casting

Bidirectional freeze casting is a versatile and promising fabrication technique employed for the production of materials with aligned and ordered microstructures in two perpendicular directions, possible in constructing centimeter-scale long-range ordered 3D structures [27, 86]. Different from conventional or unidirectional freeze casting, bidirectional freeze casting involves temperature gradients simultaneously along horizontal (ΔT_H) and vertical (ΔT_V) directions (Fig. 5a–c) [27, 87, 88]. During the freezing process, ice crystals gradually grow in both horizontal and vertical orientations, resulting in the formation of microstructures exhibiting aligned features in the two orthogonal directions [27, 89, 90].

An approach involves the use of a thermally conductive copper bridge, partially submerged in liquid nitrogen at one end and exposed to a higher-temperature environment at the other, effectively generating a dual-temperature bridge. Placing GO suspensions onto this bridge results in the creation of a horizontal temperature gradient extending from the liquid-nitrogen side to the other, along with a vertical gradient from the copper bridge to the upper suspension, as shown in Fig. 5a [87]. This thermal configuration leads to the initiation of ice crystal nucleation at the edge adjacent to the liquid nitrogen, followed by growth in both horizontal and vertical orientations. The low-temperature end of the metal plate can be effectively cooled by utilizing substances like liquid nitrogen, dry ice, or chilled ethanol, whereas the high-temperature end can be exposed to air or water for efficient temperature control [59, 89, 91]. The temperature difference between the high- and low-temperature ends, as well as the placement of the mold, determine the temperature gradients in both horizontal and vertical orientations, influencing the inter-lamella spacing within aerogels. After freeze drying and reduction, graphene aerogels with aligned lamella are resulted.

The incorporation of a polymer wedge at the bottom of the mold containing GO suspensions has been proven to be an effective method to precisely adjust the temperature gradient [92, 93]. This bottom-wedged container is situated typically on a metallic platform that is partially immersed in liquid nitrogen or other cold media to attain the necessary freezing temperatures, as illustrated in Fig. 5b [27, 94]. Ice crystals initiate at the lowest edge of the wedge, growing along both the wedge and the vertical direction. The rate of cooling and the slope angle of the wedge collaboratively determine the alignment observed in the final structures. For instance, Bai and colleagues achieved a monodomain structure—a consistent single orientation across the entire sample—with a wedge slope angle of 20° and a cooling rate of 5 or 10 °C min⁻¹ [95]. At cooling rates of 5 and 10 °C min⁻¹, the alignment was enhanced with increasing wedge angle up to 20°. However, when the cooling rate was low (1 °C min⁻¹), no long-range alignment was obtained, regardless of the wedge angle. An open-top cubic mold, comprising a thermally conductive copper bottom, a copper side, and three thermally insulating polymeric foam sides, can also be employed to create a dual-temperature gradient for bidirectional freeze casting, as shown in Fig. 5c [88]. When the mold is in contact with cold sources, the copper bottom and copper side experience notably rapid temperature reduction compared to the three polymeric foam sides, consequently establishing dual temperature gradients extending from the bottom to the top and from the copper to the polymeric foam side.

The comparison of schematic diagrams and morphologies of aerogels fabricated using bidirectional, unidirectional, and conventional freeze casting methods is illustrated in Fig. 5d–i [88]. Among these approaches, the bidirectional freeze casting method featuring dual temperature gradients (Fig. 5d) stands out for its capability to produce a highly organized large-size single-domain lamellar architecture. This architecture displays straight or undulating microstructures that are parallel to the plane of ice crystal growth (the yz plane) [96], as evidenced by the alignments observed in the cross section (the xy plane) and the longitudinal section (the xz plane) (Fig. 5e). Differently, unidirectional freeze casting yields organized microstructures solely along the direction of ice growth (the xz plane), while the plane perpendicular to the ice growth (the xy plane) exhibits multidomain alignments or honeycomb patterns, as shown in Fig. 5f, g. By comparison, the common freeze casting method (Fig. 5h) results in a less ordered microstructure in both the xy and xz planes (Fig. 5i). These distinct microstructural variations across the aerogels carry significant implications for their mechanical flexibility and multifunctional characteristics. The highly aligned graphene aerogel fabricated by bidirectional freeze casting holds the potential to possess outstanding properties, attributing to its precisely defined and well-ordered microstructure.

2.1.3 Radial Freeze Casting

Radial freeze casting involves a freezing process characterized by a radial temperature gradient typically extending from the outer-container to the center, which prompts ice crystals to grow radially inward [97]. This technique allows researchers to manipulate the freezing dynamics, leading to the creation of porous scaffolds with a distinct radial microstructure reminiscent of the natural cellular tracheid patterns. Drawing inspiration from the remarkably efficient capillary transport of water observed in trees, the concept of radial freeze casting has been harnessed to fabricate porous biomimetic structures that replicate the intricate cellular tracheid arrangements found in conifer trees [6a) creates a dynamic thermal landscape characterized by dual temperature gradients along both the vertical and the radial directions (Fig. 6b). With a significantly lower thermal conductivity of the polymer bottom than the surrounding metallic container, the ice grows predominantly in the radial direction, while both longitudinal and radial growth of ice crystals happen (Fig. 6c) [99]. After ice sublimation, highly aligned graphene aerogels with radially aligned cross sections and vertically aligned walls are obtained (Fig. 6d).

The radial freezing can also be employed for the rearrangement of building blocks in hydrogels. Lin et al. applied a radial freeze casting approach to convert reduced graphene oxide (rGO) hydrogels characterized by concentric rings into a captivating 3D interconnected network, resembling a spider-web structure [102]. This transformative process unfolded within a specialized metal mold, featuring a thermally insulated polymeric base immersed in liquid nitrogen, as shown in Fig. 6e. During freeze casting, the outer circumference of the mold makes direct contact with the frigid liquid nitrogen, creating a radial temperature gradient that triggers the growth of ice crystals from the mold's periphery towards its center. This promotes the reconfiguration of the previously separate rGO concentric-ring walls, originally formed through hydrothermal self-assembly, into a complex spider-web-like network after freeze-drying, as shown in Fig. 6f.

As elucidated in the “Unidirectional freeze casting” section, the gradual immersion of the GO suspension in liquid nitrogen results in a unidirectional ice growth. However, a captivating shift occurs when plunging the suspension in a cylindrical mold into liquid nitrogen. This swift immersion engenders an instantaneous and uniform exposure of the entire suspension to the frigid milieu, instigating the inception of temperature gradients rippling from the peripheral edges to the core of the cylinder [69]. Consequently, ice crystals grow radially, resulting in radial alignment of graphene sheets in the resultant aerogels.

Similarly, the fabrication of freestanding porous graphene aerogel beads, characterized by radially oriented channels extending from the sphere's surface to its center, was developed through the high-voltage-assisted fast casting of spherical GO suspensions into liquid nitrogen, as shown in Fig. 6g [103,104,105]. As these GO dispersion droplets were immersed in the frigid liquid nitrogen environment, an immediate and substantial temperature gradient ensued, triggering the rapid nucleation of ice crystals at the sphere's surface. The ice crystals then grew progressively from the surface towards the center of the sphere, as shown in Fig. 6g. A cross-sectional analysis unveils the presence of these radial channels, characterized by meticulously aligned graphene walls that span from the sphere's center to its surface, as showcased in Fig. 6h, i [104]. This distinct microscopic architecture imparts remarkable supercapacitive properties and exceptional water contaminant absorption capabilities to these graphene aerogel spheres, signifying the far-reaching potential of this technique in tailoring advanced material functionalities [103, 104].

2.2 Self-Assembly Induced Alignment

Self-assembly induced alignment in graphene aerogels refers to the process where GO sheets align themselves during the formation of aerogel structure, attributing to unique properties and the inherent ordering tendencies of GO LCs. At lower concentrations, colloids composed of anisotropic particles (here the GO sheets) exhibit an isotropic phase, yet they undergo a transition into a biphasic combination, characterized by the coexistence of both isotropic and nematic phases, as the particle concentration increases [106]. When the concentration of GO sheets reaches the critical transition concentration, a fully formed and distinct nematic phase becomes established, as shown in Fig. 7a [107]. The empirical critical LC concentration, C_LC, which is deduced from the well-known Onsager's theory, is determined by [107]:

$${C}_{LC}\approx \frac{4T}{W}$$

(1)

where T and W are the thickness and width of GO sheets, respectively. According to the empirical equation, we can conclude that the critical transition concentration of the GO suspensions is highly related to the aspect ratio of GO sheets.

The influence of aspect ratio on the critical concentration for the transition to the nematic phase has been experimentally confirmed through an investigation of the nematic phase fraction in GO suspensions with different sizes of GO sheets [108,109,110]. At a sufficiently low concentration of 0.1 mg mL⁻¹, the large GO (LGO) dispersion with lateral sizes ranging from 0–20 μm remained isotropic, while higher concentrations led to the coexistence of isotropic and nematic phases, resulting in observable macroscopic phase separation after standing for two weeks of self-size separation, as shown in Fig. 7b [109]. The critical concentration for LC transition was determined to be 1.0 mg mL⁻¹ for LGO dispersions. In contrast, the nematic phase in small GO (SGO with lateral sizes ranging from 0–5 μm) suspensions emerged at 2.0 mg mL⁻¹, with the complete transition to an all-liquid–crystal phase occurring at 8 mg mL⁻¹, notably higher concentrations compared to those observed for LGO suspensions.

These distinct textures observed within GO LCs serve as the essential foundation for the fabrication of highly aligned graphene aerogels through self-assembly techniques. By varying concentrations above the C_LC and employing different aspect ratios of GO sheets, a diverse array of textures can be achieved within the LC, directly influencing the eventual microscopic orientation of the self-assembled building blocks in the resultant aerogel [111]. Notably, GO LCs with a mean diameter of 1.65 μm and concentrations ranging from 0.3 to 0.5 wt% exhibited Schlieren textures characterized by disclinations of varying signs and strengths (Fig. 7c), effectively reflecting the local orientation of the GO sheets [112]. Correspondingly, SEM images of freeze-dried textured GO LCs revealed a consistent alignment of graphene around a few ± 1/2 disclinations (Fig. 7d), which is consistent with those in LCs. An intriguing long-range helical structure was also observed by Xu et al. within GO LCs [113]. Specifically, at a GO concentration of 0.98 vol%, surpassing the C_LC of 0.23 vol%, the GO LC displayed a distinct fingerprint texture, as shown in Fig. 7e, f. This unique texture was further corroborated by freeze-fracture cross-sectional SEM morphologies, revealing a well-ordered circular arrangement of GO sheets (Fig. 7g, h).

Typical self-assembly process of utilizing the in-situ gelation of the ordered GO LCs by hydrothermal treatment to maintain the alignment characteristics. This step involves sealing the GO dispersion within a high-pressure vessel and heating it under controlled conditions, typically at temperatures ranging from 80 to 200 °C [114]. The elevated temperature and pressure create an environment that promotes the reconfiguration and reduction of oxygen functional groups, as well as partial restoration of the sp² carbon–carbon bonding network in the GO sheets [115]. The hydrothermal treatment also facilitates the self-assembly of rGO sheets into three-dimensional structures due to the reformation of π-π stacking interactions, resulting in the formation of rGO hydrogels (Fig. 8a) [11, 116]. The inherent alignment of LCs remains preserved throughout the hydrothermal process due to the absence of any disruptive factors such as vibration or stirring during the self-assembly process [117, 118]. This natural preservation of order translates into graphene alignment within the resultant aerogels after freeze drying, as shown in Fig. 8b, c [119, 120].

The alignment achieved in self-assembled aerogels is intricately linked to the inherent orientation of GO LC precursors [116]. As such, factors influencing the LC order, such as the previously discussed concentration and lateral size of GO sheets, play a critical role in determining the eventual alignment of graphene sheets within the aerogels. Appropriate concentration of GO dispersion is crucial for fostering aligned microstructures during the hydrothermal self-assembly process. Insufficient concentrations lead to the absence of LC characteristics, while excessively high concentrations result in limited GO sheet mobility, hampering ordered arrangements (Fig. 8b–d) [11, 121]. Greater lateral dimensions or larger aspect ratios of GO sheets significantly enhance their anisotropic attributes, thereby being advantageous for achieving self-assembled alignment.

When employing conventional-sized GO sheets with an average size < 10 µm, the establishment of a greatly oriented LC needs a large concentration of ~ 10 mg mL⁻¹ [112]. In the pursuit of lightweight materials, or more precisely, materials with elevated specific properties when normalized by density, the creation of ordered structures within GO suspensions at lower concentrations becomes imperative. A base-induced rearrangement of GO sheets within suspensions to form highly oriented LC structures at lower concentrations has been developed. Yao et al. potassium hydroxide (KOH)-induced evolution of GO liquid crystals (3.5 mg mL⁻¹) with notably augmented ordering upon the addition of specific amounts of KOH, as shown in Fig. 8e [28]. Besides the KOH, the strong base sodium hydroxide was also proved to be effective in creating ordered laminar textures in GO LCs [122]. This evolution is a result of two synergistic factors: firstly, partial reduction of GO sheets by KOH extends their rigid domains, facilitating the creation of highly ordered microstructures; secondly, increased electrostatic repulsion between GO sheets enhances suspension fluidity, allowing GO sheets to migrate to regions of lowest Gibbs free energy [28, 122]. The impressive alignment achieved by KOH-induced ordered LCs (Fig. 8f) is seamlessly transferred to the self-assembly process, yielding graphene aerogels with analogous orientational morphologies (Fig. 8g–i).

The incorporation of electrolytes to disrupt the mutual balance of GO sheets within a solution has emerged as an effective strategy for achieving the self-assembly of graphene aerogels by overcoming electrostatic repulsion [124]. The introduction of specific amounts of electrolytes, such as acids [125], salts [126], and organics [124], triggers the formation of GO hydrogels. The electrolyte-induced assembly shares a common characteristic with other self-assembly methods, namely, that the alignment within the resulting graphene aerogels is profoundly influenced by the properties of GO LCs. In order to further enhance the alignment based on conventional GO LCs, the integration of vacuum filtration, which generates shear forces, with the electrolyte-induced assembly has been devised, as illustrated in Fig. 8j [123]. This innovative approach disrupts the electrostatic equilibrium between GO sheets through the introduction of electrolytes, leading to the formation of GO microclusters. Simultaneously, the application of vacuum filtration-driven external forces is harnessed to intensify alignment, thereby fostering the development of a finely tuned and ordered structure (Fig. 8k, l).

2.3 Shear-Induced Alignment

GO dispersions exhibit shear-thinning behavior, characterized by a reduction in viscosity when subjected to shear stress [127]. This phenomenon arises from the realignment and reorientation of GO sheets, causing the disruption of interactions between the sheets. Initially, the presence of randomly dispersed GO sheets leads to a high viscosity due to their mutual interactions. However, the shear stress prompts the GO sheets to align and reorient, decreasing the resistance to flow and subsequently reducing viscosity [127]. The network-like structure formed by GO sheets, combined with their high aspect ratio and functional groups, contributes to the shear-thinning behavior. Upon shearing, GO suspensions can transition from a colloidal isotropic state to a nematic liquid crystal phase [128]. When the concentration of GO dispersion falls below the threshold for biphasic-to-nematic transition, the shear rate-dependent GO structure manifests non-Newtonian properties. At low shear rates, the low-concentration GO suspension displays weak shear-thinning behavior, while a shear-thickening behavior becomes apparent at high shear rates, as exemplified by the Taylor vortex flow in Fig. 9a [129]. In cases of high GO concentration, the more distinguished shear thinning results in the emergence of distinct stripe patterns as shear rates increase, ultimately leading to the formation of highly oriented GO liquid crystals (Fig. 9a).

The shear-thinning properties of GO liquid crystals enable the reconfiguration of GO sheets within the liquid crystal phase. Utilizing mechanical shearing by means of a rod or wire to scratch GO liquid crystals induces the reorientation of GO sheets in the direction of the shear [130]. Over a certain period, this reorientation may gradually subside, with the relaxation time directly correlated to the concentration of GO, as shown in Fig. 9b [131]. In the isotropic phase at lower GO concentrations, GO sheets exhibit a random distribution and engage in independent oscillations near their equilibrium positions, following a Brownian rotational motion. Following a single shearing event, relaxation occurs within tens of seconds. Conversely, the alignment of GO sheets achieved through shearing within the nematic liquid crystal phase remains stable for over 30 days, which suggests that a concentration larger than the C_LC is required for the fabrication of highly aligned graphene aerogels via shearing-induced alignment.

The mechanism underlying the shear-induced reorientation of GO sheets is elucidated in Fig. 9c–e [131]. As a rod moves within GO suspensions, it engenders a flow-around-pole phenomenon [132], giving rise to a shear field surrounding the in-motion rod, as shown in Fig. 9c. The width (W) of these localized Stokes flows is related to the rod’s radius and its moving velocity (v), and this relationship can be estimated using:

$$W=2\left(1+\sqrt{\frac{v}{{v}_{cr}}}\right)R$$

(2)

where the v_cr is the critical velocity to mobilize GO sheets. As the rod radius increases or the moving speed intensifies, the width of the reoriented GO suspensions expands (Fig. 9d, e). A GO LC possessing a viscosity of ~ 100 Pa·s and a density of ~ 10³ kg m⁻³ was employed to visualize the intriguing phenomenon of shear-induced GO sheet rearrangement. Through scratching the tape-casted GO LCs, where the GO sheets are predominantly aligned parallel to the plane, vertical alignment of GO sheets formed. This intriguing observation, depicted by the highlighted regions in Fig. 9f, holds the potential for practical applications in engineering the conformational aspects within LCs.

On the basis of shear-thinning phenomenon and shear induced alignment of GO suspensions, two typical aligning techniques have been extended for the fabrication of highly aligned graphene aerogels, namely the flow induced alignment (Fig. 10a–d) and the shearing microlithography (Fig. 10e–h). The technique of uniaxial flow has been widely embraced to induce the alignment of GO sheets along a specific flow direction. This approach, when combined with a subsequent freeze-casting process, unveils a promising avenue for crafting graphene aerogels with exceptionally high alignment. The general procedure involves loading GO LCs into a syringe, followed by controlled extrusion through a nozzle at a carefully regulated speed into a frigid bath. Notably, the aligned GO sheets within the LCs come to the fore at the nozzle region and steadfastly maintain their alignment as they freeze in the cold bath, as vividly illustrated in Fig. 10a [133]. Following the subsequent freeze-drying step, this resulting aerogel manifests a morphology akin to that achieved through unidirectional freeze casting techniques. As shown in Fig. 10b, c [55], the material showcases aligned graphene sheets running parallel to the flow direction, while the cross-section reveals a multi-domain tubular structure.

The flow-induced alignment can also be combined with 3D printing to fabricate carefully designed hierarchical graphene aerogels. A case in point is the work by Wang et al., who achieved the fabrication of a high-density graphene aerogel microlattice with an ordered structure through the direct ink writing of glycerol-functionalized GO LCs [134]. They yielded a striking outcome with highly aligned filaments within the structure. Furthermore, when employing a slit extrusion head, the potential of producing planar graphene aerogels with horizontally aligned building blocks becomes feasible. This was achieved through a layer-by-layer deposition of GO dispersions on a cooled platform, followed by freeze-drying, as illustrated in Fig. 10d [29]. It's noteworthy that the specific morphology of the printed graphene aerogel is intricately intertwined with the printing speed and the diameter of the slit extrusion, imparting a tunable quality to the process.

The method of shearing microlithography entails the movement of a stick within the GO LCs, a process that facilitates the emergence of macroscopically aligned two-dimensional (2D) GO nanosheets. The outcome of this procedure is visually striking, revealing distinct dark and bright textures that represent the anisotropic optical responses of the meticulously ordered GO nanoflakes [135]. The larger GO sheets, boasting a greater aspect ratio, exhibit a more pronounced moment of force under the influence of the shearing field [108]. This engenders a larger driving force, enabling them to overcome the resistive hydrodynamic drag within the viscous suspension [136]. In a similar vein, the orientation of graphite oxide suspensions can also be meticulously controlled through shearing, serving as a valuable reference for aligning GO. A boundary-free vertically-moving microwire shearing technique has been implemented to achieve a precise vertical orientation of colossal graphite oxide sheets, as vividly depicted in Fig. 10e [137]. Large-scale vertical arrays of giant graphite oxide flakes were fabricated by narrowing the interval spacing (S) between adjacent shearing fields. The initial cycle of this process resulted in a π wall, signifying a distinct nonuniform structure marked by vertical alignment within the central domain transitioning to horizontal alignment at the boundaries, where the width (W) spanned 50 µm [137]. With a favorable S/W ratio of 0.1, a remarkably well-aligned porous microstructure emerged, displaying an intriguing anisotropic skeleton with bidirectional sheet ordering.

Vertical alignment of GO sheets can be effectively achieved through the horizontal sliding of a probe immersed within the GO suspension. This technique allows for the digital programming of GO LCs, offering the capability to program the alignment or texture of GO sheets. Different moving routines of the microprobe can be employed to achieve precisely programmed alignment patterns [138]. In cases where the probe is guided towards a specific direction within a sufficiently small interval, a uniform and distinctly vertical alignment of GO sheets is realized, as schematically illustrated in Fig. 10f, g [131]. Through a meticulous freeze-drying process, this vertical alignment phenomenon becomes an inherent trait of the resultant graphene aerogel, as exemplified in Fig. 10h.

2.4 Further Enhancement of Alignment

While GO presents a promising foundation for the construction of aligned graphene aerogels, its extensive oxygen-containing groups, particularly hydroxy groups, situated on the basal plane of GO, lead to the creation of more hydrogen bonds with ice crystals than with liquid water. This intricate interaction inhibits the growth of ice crystals [139], consequently impeding the alignment in resulting aerogels even under the conditions of unidirectional or bidirectional freeze casting. Efforts have been made to mitigate the interactions between GO sheets and ice crystals that form in situ, aiming to enhance alignment within GO architectures, including, (i) antifreeze-assisted freezing [30], (ii) cation-assisted freezing [35], and (iii) additional thawing and freezing [140] (Fig. 11).

Organic solvents, widely recognized as potent antifreeze agents, exert a notable influence on the freezing dynamics, altering the crystallization patterns of ice crystals via their interaction with hydrogen bonds [150]. The architectures of rGO aerogels originating from partially reduced GO microgels are subsequently modulated during the ensuing freeze-thaw phase. Central to this is the fine-tuning of inter-sheet π-π interactions during the supplementary thawing and reduction phases. This optimization confers a robust structural framework that withstands the additional ice growth process [151]. Through subsequent cycles of thawing and freezing, the arrangement of rGO sheets is further refined, culminating in heightened alignment of constituent building blocks and the realization of highly oriented graphene aerogels [149].

2.5 Comparison of the Aligning Techniques

Based on the above discussion regarding the fabrication of aligned graphene aerogels, a comparative overview is summarized in Table 1. Driving forces of the directional freeze casting, self-assembly and shear-induced alignment are the growth of ice crystals, reduction-induced gelation, and shearing, respectively. Morphologies of graphene aerogel fabricated by directional freeze casting is highly related to the direction of temperature gradient, whereas self-assembly and shearing induced alignment is dependent on the orientation of GO LCs and the shearing direction, respectively (Fig. 2). Lamellar structure can be obtained from the bidirectional freeze casting and shearing forced aligning. Long-range alignment is easy to be obtained by techniques except self-assembly induced aligning. Owing to their highly aligned lamellar structure and remarkable superelasticity, bidirectionally freeze-cast graphene aerogels find particular applicability in pressure sensing and thermal management applications. Meanwhile, the radial alignment in radially freeze-cast aerogels affords ample surrounding channels for the movement of organic solvents and oils, making them advantageous for organic absorption applications.

Table 1 Comparisons of different aligning techniques for graphene aerogels

Full size table

The costs of different fabrication techniques provide important information for industries manufacturing. The relative fabrication cost of the aligning techniques discussed in this review are summarized in Table 1. The directional freeze casting method involves a freezing process using cold sources, such as liquid nitrogen or chilly ethanol. The freezing period is relatively short because of the ultralow-temperature cold source, taking about tens of minutes. The design of the freezing mold, generally made by polymers and metals, and the temperature gradient are the key to control the direction of ice growth. With the mold and cold source being main expenses of the directional freeze-casting (no complicated equipment), the easy-processing freeze casting technique are relatively cheap and time-efficient, being the most promising aligning technique for large-scale applications [26, 152]. However, careful optimization of freezing parameters is required for long-range alignment. The self-assembly aligning technique involves reduction induced gelation of GO LCs, generally a hydrothermal process at temperature ranges of 60–200 °C for about a few hours to over 1 day [28, 53, 126]. Taking the electronic energy and time cost into account, the cost for self-assembly method lies in-between the directional freeze casting and shear induced aligning. The shear-induced aligning techniques, including flow induced aligning and shearing microlithography of GO LCs, are promising for large-scale fabrication of graphene aerogels with long-range alignment, but the cost of equipment for large aerogels are relatively high. Besides, large-size, high-concentration GO LCs are required, increasing the cost of raw material and make this technique the most expensive among the three aligning techniques [29, 137, 153]. While the freeze casting method demonstrates scalability and a cost advantage compared to other aligning techniques, the overall cost of the graphene aerogel fabrication process remains relatively high for large-scale industrial applications. This mainly includes expenses associated with the costly GO suspension, freeze casting, freeze drying, and post-treatments (such as chemical reduction and high-temperature annealing), limiting practical applications of graphene aerogels.

2.6 Fabrication of Highly Aligned Graphene Aerogel/Polymer Composites

One approach for fabricating aligned graphene aerogel/polymer composites involves constructing highly aligned graphene aerogels followed by polymer infiltration, as shown in Fig. 12a [154]. In this methodology, the foundation lies in the fabrication of highly aligned graphene aerogels, a task achieved through diverse means such as template-based methodologies, self-assembly, or precision alignment techniques like shearing. These strategies confer meticulous command over the spatial orientation of graphene within the aerogel's intricate architecture. Once the coveted highly aligned graphene aerogels are realized, they are subsequently infused with a polymer solution or precursor, facilitating the complete impregnation of the polymer matrix into the porous aerogel framework. This meticulous infiltration ensures an intimate interlocking between the polymer and the pre-existing aligned graphene scaffold. Subsequently, the solvent is extracted or the polymer is cured, obtaining an aligned graphene/polymer composite [143]. Importantly, post-polymer infiltration, the profound orientation of graphene walls within the aerogel remains impeccably preserved, as shown in Fig. 12b, c. The resultant composite material showcases significantly enhanced mechanical, electrical, and thermal attributes, rendering it a versatile contender for a spectrum of applications [155].

An alternative avenue for crafting aligned graphene /polymer composites aerogel involves the technique of directional casting of graphene/polymer solutions, as shown in Fig. 12d. This method entails the preparation of a graphene/polymer solution, achieved by uniformly dispersing graphene within a polymer solution to obtain a homogenous solution or suspension, typically an aqueous medium. The ensuing step encompasses the casting or pouring of this solution into a designated mold, subsequently subjecting it to the aligning procedures elucidated earlier. Following the freeze-drying phase, the resultant composite aerogel embodies the framework of aligned graphene/polymer composite walls [156]. Notably, these aligned graphene/polymer composite aerogels can also be subjected to external compressive forces for the fabrication of composites, ultimately culminating in the formation of solid composites furnished with oriented graphene fillers (Fig. 12e) [157].

Overall, both methodologies present potent avenues for the creation of aligned graphene aerogel/polymer composites, each proffering distinct merit. The first approach centers on the meticulous fabrication of highly aligned graphene aerogels, followed by polymer impregnation, obtaining aligned 3D interconnected graphene aerogel networks within composites [143]. Conversely, the second technique employs the directed casting of graphene/polymer solutions, promoting the simplicity and scalability. Uniformly dispersed and aligned graphene sheets in the aligned skeletons are generally obtained. The ultimate choice between these methods relies on factors such as the desired level of alignment control, scalability, and the specific requisites of the intended application [158].

3 Fundamental Properties

3.1 Anisotropic Properties

The carbon atoms constituting the graphene lattice are intricately linked through robust covalent bonds, forming a resilient 2D structural framework. Due to the atomic structure and bonding, graphene exhibits intrinsically anisotropic properties, which lead to anisotropy in highly aligned graphene aerogels. The directional dependence of graphene's properties extends to the aerogel structure when graphene sheets are aligned within it. This directional dependency inherent to graphene's properties becomes entwined with the aerogel's characteristics, thereby imparting direction-specific qualities. As a consequence of the alignment, the aerogel's mechanical, electrical, thermal, transport, EMI shielding, and other properties are significantly influenced along different orientations. For the sake of clarity in our discussion, the directional aspects of properties are graphically represented in Fig. 13a, b.

The anisotropy of mechanical stiffness and hysteresis of aligned graphene aerogel and their composites have been demonstrated by researchers [58, 89]. In bidirectionally freeze-dried graphene aerogel, the alignment of graphene creates a continuous load-bearing network, enabling efficient stress transfer and resulting in higher stiffness along the aligned direction (the y direction), as shown in Fig. 13c [33]. Conversely, the absence of a continuous alignment perpendicular to the aligned direction (the x direction) leads to lower stiffness. As a comparison, the unidirectionally freeze-dried graphene aerogels show similar stiffnesses in the x and y directions (Fig. 13d), both being subordinate to that observed in the z direction [33]. This is due to the isotropic porous structure within the xy plane and the alignment of skeleton along the y direction [159]. The comparison of mechanical properties between bidirectionally and unidirectionally freeze-dried graphene aerogel confirms the contributions of graphene alignment to macroscopic properties. Hysteresis, indicative of energy dissipation during cyclic loading and unloading, generally exhibits lower values perpendicular to the alignment, predominantly because of weaker frictions among graphene sheets and gentler airflow within the porous structure during deformation [37, 58]. Consequently, highly aligned graphene aerogels show super-elasticity exceptional and resilience upon cyclic compression [160,161,162]. An example is that the bidirectional freeze-casting graphene aerogels a 96% recovery of height after a compression to 90%, as shown in Fig. 13e [33]. The anisotropic mechanical properties of aligned graphene aerogel can be inherited their composites, showing different stress–strain characteristics along different directions [154].

The delocalized π-electrons within the carbon hexagonal lattice enable electrons to move unrestrictedly along the graphene plane, rendering high electrical conductivity along its in-plane direction. This characteristic extends to graphene aerogels and their composites, where aligned graphene conductive frameworks give rise to anisotropic electrical conductivity, marked by enhanced conductivity along the aligned axis and diminished conductivity perpendicular to it [34]. An illustrative example of this phenomenon is observed in the research by Wang et al. who investigated anisotropic electrical conductivities in graphene aerogel freeze-dried from GO suspensions of varying concentrations, as shown in Fig. 13f [5]. The anisotropy of electrical conductivity in graphene aerogels becomes more pronounced with higher concentrations of GO, attributing to increased alignment of graphene sheets induced by the elevated GO concentration. Similarly, Gao et al. reported on highly aligned graphene aerogel/PDMS composites displaying electrical conductivity notably higher by 1–2 orders of magnitude in the z direction compared to the x direction [154]. The anisotropy in electrical conductivity is attributed to the aligned graphene sheets within the aerogel structure, which establish a continuous conductive network along the alignment direction and an inconsecutive bridging structure in the transverse direction, thus enabling more efficient electron transport and higher conductivity along the direction of alignment (Fig. 13g).

The interplay of convection, conduction, and radiation mechanisms significantly influences the anisotropic thermal conductivity observed in aligned graphene aerogels. The arrangement of graphene sheets within the aerogel creates an uninterrupted conductive network, facilitating efficient electron and phonon transport and consequently enhancing thermal conduction [34], as illustrated by the solid blue arrows in Fig. 13h. Notably, the thermal conduction occurring between the aligned graphene skeletons is markedly higher along the alignment direction [34], owing to the relatively lower thermal conductivity of air present among aligned graphene walls. Additionally, the occurrence of thermal convection perpendicular to the alignment is negligible due to the limited pore size among the graphene walls, which restricts the onset of natural thermal convection [163]. The distinctive anisotropic structure also enhances heat dissipation along the z direction, preventing heat accumulation [34]. Consequently, aligned graphene aerogels exhibit anisotropic thermal conductivities, showing remarkably higher thermal conductivity along the alignment direction compared to the perpendicular direction [37, 64, 159]. When graphene aerogel-based composites are formed by infiltrating polymers into the pre-constructed porous graphene architectures, the anisotropic thermal conducting traits of aligned graphene aerogels extend to these composites as well [164, 165]. An illustrative example by Liu et al. involves the fabrication of lamellar-like graphene aerogels through bidirectional freeze-casting, succeeded by compaction perpendicular to the alignment direction and vacuum-assisted impregnation with epoxy to produce composites featuring a high alignment of graphene fillers [166]. These composites demonstrate a notable anisotropy in thermal conductivity, exhibiting around 20 and 17.5 W m⁻¹ K⁻¹ along the z- and y- direction, respectively. However, the thermal conductivity decreases substantially to about 1.2 W m⁻¹ K⁻¹ along the x-direction, which is perpendicular to the alignment, as shown in Fig. 13i.

Graphene sheets possess exceptional barrier properties that effectively block the transport of matter through their plane, owing to the tightly packed atomic structure strong bonding energy, and unique electronic configuration of graphene [167]. These factors collectively create a robust barrier that prevents the passage of molecules or atoms through the graphene sheet [168]. Aligned graphene aerogels capitalize on this inherent barrier capability by featuring porous channels oriented along the alignment direction and stacked graphene walls in the transverse orientation. This structural arrangement gives rise to intriguing anisotropic transport characteristics, as illustrated in Fig. 13j, k. The aligned pores establish preferential pathways for the transport of molecules, ions, and substances, offering a conduit for efficient movement. On the contrary, the walls, composed of densely stacked graphene building blocks, exhibit significantly greater resistance, limiting the transport of substances perpendicular to the alignment. This leads to the distinct anisotropic transport properties observed in aligned graphene aerogels, where molecular or atomic movement becomes directionally dependent.

The EMI shielding of materials is attributed to reflection, absorption, and multiple reflection of electromagnetic waves [169]. The reflection of electromagnetic radiation is fundamentally a consequence of the interaction between waves and free charges present on the material's surface, which suggest that the presence of conductive networks characterized by a substantial concentration of charge carriers significantly contributes to the efficacy of reflection-based EMI shielding effectiveness (SE). The SE associated with absorption quantifies a material's capacity to attenuate electromagnetic radiations into thermal or internal energies, which is achieved through processes such as the generation of localized currents within conductive networks, the polarization or relaxation of dipoles and charges, and the charge delocalization [170]. An integral aspect that emerges from these mechanisms is the evident correlation between the EMI shielding properties of materials and their electrical conductivities. Therefore, the anisotropic electrical conductivity intrinsic to aligned graphene and its composites naturally gives rise to anisotropic EMI shielding properties (Fig. 13l) [82, 154, 171]. As electromagnetic radiation penetrates graphene aerogels from a direction perpendicular to the alignment, the waves experience a series of reflections and scatterings at the numerous interfaces presented by the oriented graphene walls. This continuous back-and-forth interaction contributes to the gradual dissipation of electromagnetic waves into thermal energy (Fig. 13m) [171]. But when the waves approach the aerogels parallel to the aligned graphene frameworks, their penetration is comparatively unhindered, leading to a reduction in the dissipation of incident radiations [34, 172].

3.2 Contributions of Alignment to Physical Properties of Composites

3.2.1 Electrical Conductivity

Percolation Theory Electrically conductive materials have diverse applications in electronics, energy storage, sensors, EMI shielding, wearables, automotive systems, and aerospace, emphasizing their essential role in modern technology. When conductive additives are introduced into insulating polymers, the electrical conductivity of the resulting composites undergoes a distinct transition from an insulating to a conducting state as the concentration of conductive components or pathways within the material surpasses a specific threshold, which is well-known as the percolation phenomenon [173]. In the region below this threshold, the composite material behaves as an insulator, displaying minimal to negligible electrical conductivity. However, once the threshold is exceeded, the material makes a pivotal shift into a conductive state, with electrical characteristics becoming exceptionally responsive to the concentration and arrangement of the conductive constituents, as shown in Fig. 14a [174].

The transition is often described as a critical connectivity point where a continuous conductive pathway forms across the material, allowing the flow of electric current. The percolation threshold is a specific concentration value above which the material's conductivity increases dramatically, which can be estimated based on the power law equation [175]:

$$\sigma \propto {\sigma }_{f}{(V-{V}_{p})}^{a}$$

(3)

where σ and σ_f are the electrical conductivity of composite and filler, V and V_p represent the filler volume fraction and the percolation threshold, and a is a critical exponent. In essence, the percolation phenomenon elucidates the intriguing interplay between the arrangement and concentration of conductive elements within a composite material, fundamentally influencing its electrical properties.

The percolation threshold of various graphene/polymer composites containing different networks of graphene are plotted in Fig. 14b. The composites reinforced with large-aspect-ratio chemical vapor deposition (CVD) grown graphene sheets characterized by a high aspect ratio exhibited remarkably low percolation thresholds, attributing to the pristine lattice structure and the extensive aspect ratio of these graphene sheets [176, 177]. Interestingly, pre-fabricated composites incorporating aligned graphene aerogels showcased exceptionally low percolation thresholds of approximately 0.007 vol% [5, 65]. This strikingly low value is primarily a result of the formation of conductive networks within the well-ordered walls of the aerogel architecture, achieved at an impressively modest filler content. However, an aligned graphene aerogel created through a hydrothermal-induced self-assembly process exhibited a comparatively higher percolation threshold of 0.12 vol% [11], resulting from the stacking of GO building blocks during the hydrothermal process. Comparatively, composites containing randomly oriented graphene aerogels exhibited notably higher percolation thresholds than those composed of aligned graphene aerogels [178, 179]. Composites consisting of random graphene aerogels showed relatively lower or comparable percolation thresholds than those with dispersed graphene sheets [180,181,182,183,184,185]. The segregated graphene reinforced composites [186,187,188,189], generally fabricated by hot compression of graphene coated polymer spheres, displayed percolation thresholds comparable to the random graphene aerogel reinforced composites. In a comprehensive assessment of various graphene network types within polymer composites, it is evident that the aligned aerogel architecture emerges as a promising option.

Electrical Conductivity Upon surpassing the percolation threshold, the electrical conductivity of graphene/polymer composites exhibited a distinct transition from insulating to conducting, showing a rapid surge in electrical conductivity near the percolation threshold followed by a more gradual increase (Fig. 14a). A comprehensive comparison of graphene/polymer composites featuring different graphene network configurations is illustrated in Fig. 14c. Composites reinforced with graphene aerogel, dispersed graphene and segregated graphene commonly employ GO as the graphene precursor, as the precursor for graphene, owing to its ease of processing and favorable compatibility with polymer matrices. The attainment of electrical conductivity is realized through the partial reduction of the GO precursor, resulting in the effective conducting component of rGO within the composites. According to Fig. 14c, it is evident that aligned graphene aerogels represent the most effective rGO fillers among these categories [5, 65, 171, 190], because the arrangement of interconnected rGO building blocks in the oriented aerogel framework serves as efficient conductive pathways. Noteworthy examples include unidirectional freeze-cast graphene aerogel/epoxy composites, where the oriented aerogel frameworks yielded a commendable conductivity of 13.5 S m⁻¹ at a minimal filler content of 0.11 vol% [65]. Furthermore, through a combination of hydrothermal and unidirectional freeze-drying processes, aligned graphene aerogels with enhanced wall thicknesses were achieved, leading to composites exhibiting an electrical conductivity of 980 S/cm at a filler content of approximately 0.4 vol% [171]. In contrast, the randomly oriented graphene aerogel, despite possessing a 3D network similar to that of highly aligned graphene aerogel, exhibited a comparatively less effective conductive behavior due to its more convoluted network structure [178, 191, 192].

Dispersed graphene reinforced polymer composites are commonly prepared using solution processing. With good dispersion and sufficiently large content of graphene, conductive networks can be formed. However, due to the inherent challenge in achieving uniform dispersion of graphene and rGO within polymer matrices, composites containing dispersed graphene sheets often exhibit a certain degree of agglomeration of the filler. This, in turn, results in relatively diminished electrical conductivities, even at higher filler contents [180, 196,197,198,199]. In the process of fabricating composites via the hot compression of graphene-coated polymer particles, segregated graphene-rich regions spontaneously form, engendering electrically conductive pathways. The inherent segregation of graphene within the polymer matrix gives rise to continuous three-dimensional networks, fostering electrical conduction and leading to relatively higher electrical conductivity compared to composites with dispersed graphene configurations [187,188,189, 200]. Composites incorporating networks of graphene grown via CVD, including graphene foam (GF) [177], graphene woven fabric (GWF) [194], and multilayer graphene web (MGW) [195], have demonstrated the most exceptional electrical conductivities within polymer composites. These exceptional conductivities of CVD-grown graphene reinforced composites are attributed to the 3D continuous network and the flawless graphitic structure of the graphene framework.

In summary, from the above comprehensive analysis of the electrical conductivity of graphene/polymer composites featuring different building blocks and structural arrangements, we can conclude that the contribution of these materials to electrical conductivities of composites follows a general trend: CVD-grown graphene network > highly-aligned graphene aerogel > randomly oriented graphene aerogel ≈ segregated graphene > dispersed graphene. Considering that the intrinsic electrical conductivity of rGO building blocks in graphene aerogels is significantly lower than that of graphene building blocks in CVD-grown networks, the pronounced contribution of the aligned structural configuration to enhanced electrical conductivity is evident.

3.2.2 Fracture Toughness

Fracture toughness is a material property that quantifies a material's resistance to fracture or failure when subjected to a crack or other forms of stress concentration. It indicates the amount of energy a material can absorb before fracturing, which is a critical parameter for assessing a material's ability to withstand mechanical loads and resist crack propagation. Indeed, fracture resistance holds even greater significance and importance in practical engineering applications compared to modulus and strength. To gain insights into the contribution of highly-aligned graphene aerogels on composite toughness, a comparison of fracture toughness enhancement with the inclusion of various graphene additives is depicted in Fig. 15a.

The utilization of highly aligned graphene aerogels as reinforcement in epoxy composites results in significant enhancements in fracture toughness. An increment of 98% was witnessed in unidirectional freeze-cast graphene aerogel-reinforced epoxy composites, where the filler content was 2.4 vol% [201]. Epoxy composites incorporating highly aligned graphene aerogels, manufactured through the directional casting of large-size GO suspensions, experienced a notable enhancement of approximately 70% at a meager filler content of 0.11 vol% [65]. Another remarkable case is observed in bidirectional freeze-cast graphene aerogel-reinforced epoxy composites, featuring a bio-inspired nacre structure, which achieves a substantial increment of about 85% at a filler content of 0.65 vol% [202].

As comparisons, with equivalent rGO building blocks, it is evident that the aligned graphene aerogel [11, 42, 65, 143, 166, 201, 202] outperforms the randomly oriented graphene aerogel [65] and dispersed graphene [203,204,205] in terms of fracture toughness enhancement. CVD-grown graphene networks exhibit substantial impacts on the enhancement of the fracture toughness of epoxy-based composites. Notably, an exceptional enhancement of 50–70% can be achieved with a low graphene loading ranging from 0.005 to 0.28 vol% [177, 194]. At higher graphene contents, for instance, 4.1 vol% in the case of MGW, the enhancement reached approximately 108% [195]. With comparable enhancements in fracture toughness between composites reinforced by aligned graphene aerogel and CVD-grown graphene, we can see the significant role of the aligned structure in improving fracture toughness when taking into account the exceptional mechanical properties of nearly flawless and seamlessly continuous CVD-grown graphene.

The distinctive toughening mechanisms responsible for the substantial enhancement of fracture toughness in aligned graphene aerogel/epoxy composites are mainly attributed to the graphene framework induced crack reorientation. As shown in Fig. 15b–d, aligned graphene aerogel/epoxy composites exhibited fracture surfaces with a rough, stair-like appearance, as cracks were deflected by the aligned layers of GO [11]. This deflection resulted in the dissipation of a significant amount of energy, consequently leading to enhanced fracture toughness. The aligned graphene aerogels effectively blunted and diverted crack tips along the interfaces between rGO and epoxy, which effect was visually evident from the fracture surfaces, consisting of smooth epoxy regions measuring around 20–30 µm (subject to the aerogel fabrication process) in size, interspersed by the rGO networks.

3.2.3 Thermal Conductivity

Thermally conductive polymer composites enhance thermal management in industries ranging from consumer electronics to automotive and aerospace. They find crucial applications in efficient heat dissipation for high-power electronic devices and batteries, enabling improved device performance and reliability. Graphene, with its exceptionally high in-plane thermal conductivity of 5300 W m⁻¹ K⁻¹ [206], holds great promise for enhancing the typically low thermal conductivity of polymers of 0.1–0.3 W m⁻¹ K⁻¹. To maximize the contribution of graphene additives, a high quality of graphene additives is important. Highly-aligned graphene aerogels with well-crystalline structures induced by thermal annealing at 2800 °C (pink area in Fig. 19a) [64, 74, 137, 166, 207] significantly outperform partially reduced and aligned counterparts (orange area) [102, 201, 208]. Composites reinforced with aligned graphene aerogel reduced at 2800 °C achieved a remarkable thermal conductivity of approximately 6.6 W m⁻¹ K⁻¹ at a mere 0.77 vol% graphene content (solid stars) [64], while a much higher filler loading of around 2.3 vol% rGO was necessary for an even lower thermal conductivity of 2.6 W m⁻¹ K⁻¹ (red hollow hexagons) [102]. The superior thermal conductivity of high-quality graphene arises from reduced defects and minimized scattering of phonons or electrons, as shown in Fig. 16b, c [15].

The arrangement and alignment of graphene play a pivotal role in enhancing the thermal conductivity of graphene/polymer composites, as illustrated in Fig. 16a. Highly-aligned graphene aerogels, thermally reduced at 2800 °C [64, 74, 137, 166, 207], outperform random graphene aerogels [208,209,210], dispersed [211,212,213] and segregated rGO or graphene nanoplatelet (GNP) [214,215,216,217] in enhancing thermal conductivities of composites. They can even surpass the thermal conductivity of CVD-grown graphene/polymer composites [195, 218,219,220]. A polymer composite reinforced with 2800 °C-reduced bidirectionally freeze-cast graphene aerogel, possessing lamellar alignment and high-quality graphene building blocks, achieved an impressive thermal conductivity of approximately 20 W m⁻¹ K⁻¹ along the alignment direction at a graphene content of 2.2 vol% [166]. A high filler content of 14.8 vol% was achieved by 2800 °C-annealed shear-aligned graphite oxide array, contributing to an exceptionally high thermal conductivity of 93 W m⁻¹ K⁻¹ along the alignment [137]. In composites reinforced with CVD-grown graphene, the presence of vertically oriented graphene nanowalls [219] results in higher thermal conductivity compared to composites with random graphene networks [195, 218, 220], providing additional evidence for the beneficial impact of alignment.

The strategies devised to achieve elevated thermal conductivities in composites across various length scales are illustrated in Fig. 16d [195]. At the nanoscale, the 2800 °C annealed graphene building blocks showcase almost flawless crystallinity, leading to a scarcity of phonon scattering sites and yielding graphene sheets with remarkably high intrinsic thermal conductivities. On the microscale, the stacking and interconnection of graphene sheets within aerogel walls facilitate efficient phonon transfer across interfaces due to closely aligned phonon vibrational frequencies. On a larger microscopic scale, the organized alignment of graphene sheets constructs aerogel walls that substantially decrease phonon scattering at filler/polymer interfaces, thereby promoting extended-range phonon transport.

4 Quantitative Characterization Techniques of the Graphene Alignment

4.1 SEM Image-Based Orientation Distribution Analysis

SEM and transmission electron microscopic observations are a highly visualized techniques for alignment characterization, elucidating micro- and nano-scale morphologies across different orientations, respectively [222]. On the basis of SEM images, the extent of alignment finds quantitative assessment through orientation distribution analysis [223, 224]. This method conventionally involves the selection of a statistically substantial graphene sheet pool from SEM captures. Subsequently, reference lines are inscribed on these images, and the acute angles (η) between the reference line and individual graphene sheets are recorded, enabling rigorous quantitative analysis [5]. The orientation distribution function, N(η), is suitably modeled using the GaussAmp peak function:

$$N\left(\eta \right)={N}_{0}+A{e}^{-\frac{{(\eta -{\eta }_{c})}^{2}}{2{w}^{2}}}$$

(4)

where N₀, A and η_c are the baseline height, peak amplitude, and the angle corresponding to the peak center, respectively. The quantification of the angular displacement from the peak center, denoted as w, is ascertained through the full width at half maximum (FWHM), as outlined below:

$$w=\frac{FWHM}{2\sqrt{ln4}}$$

(5)

The degree of graphene alignment is quantitatively assessed using the average orientation angle, ⟨cos² η⟩, with respect to the preferred orientation direction. The ⟨cos² η⟩ defines the proportion of graphene sheets within the angular element, dη, as indicated by [225]:

$$\langle {cos}^{2}\eta \rangle =\int_{0}^{\pi /2}N\left(\eta \right){cos}^{2}\eta sin\eta d\eta$$

(6)

where N(η) determines the portion of graphene falling within the angular interval dη and satisfies the normalization function:

$$\int_{0}^{\pi /2}N\left(\eta \right) sin\eta d\eta =1$$

(7)

Wang et al. quantitatively describe the alignment degree in unidirectionally cast graphene aerogels by the average orientation angle [5], a concept that also extends to the assessment of filler alignment in composites [175]. The parameter ⟨cos² η⟩ serves as a metric for the alignment, which effectively characterizes the degree of orientation. The ⟨cos² η⟩ values of 0 and 1 indicate elements that are respectively perpendicular to or aligned along the preferred orientation, while a ⟨cos² η⟩ value of 1/3 signifies a 3D random distribution of graphene sheets. Application of the orientation distribution analysis to a typical unidirectional freezing graphene aerogel reveals a distribution of graphene sheets spanning from − 90° to 90°, as shown in Fig. 17a, d. This distribution exhibits a pronounced peak at around 0°, signifying the alignment of graphene sheets along the unidirectional casting direction (Group 1), alongside a less prominent peak centered at approximately ± 90°, corresponding to bridging elements amidst alignments (Group 2), as shown in Fig. 17g. Evaluating ⟨cos² η₁⟩, which pertains to the orientation angles of the predominant group (Group 1), elucidates that graphene sheets in aerogels fabricated using 1 mg mL⁻¹ GO dispersions (Fig. 17b, c) achieved a higher degree of alignment compared to those prepared with 0.5 mg mL⁻¹ GO (Fig. 17e, f).

4.2 Polarized Raman Spectroscopy

Polarized Raman spectroscopy is a highly effective and widely embraced technique for characterizing the graphene alignment within diverse materials, which offers an efficient and non-destructive approach for assessing alignment quality, orientation, and the anisotropic attributes of graphene-based materials. A schematic representation of a typical polarized micro-Raman setup is presented in Fig. 18a. This apparatus enables precise control over the polarization of incident laser beams and facilitates the analysis of Raman-scattered light through the utilization of linear polarizers and wave plates [226]. The Raman scattering process within graphene is resonant, rendering it indifferent to the energy of the excitation laser. A wide spectrum of laser wavelengths, ranging from the infrared to the near ultraviolet, can be employed. Through an analysis of the intensity variations in the G- or 2D-band within the Raman spectrum, researchers can extract quantitative insights into the alignment characteristics of graphene within diverse materials. This analytical capability empowers researchers to fine-tune and regulate alignment processes, thereby achieving the desired properties tailored for specific applications.

The Raman spectra of graphene and its derivatives typically possess a D-band (~ 1350 cm⁻¹) arising from vibrations at defects like vacancies, grain boundaries, and heteroatoms within graphene sheets, a G-band (~ 1580 cm⁻¹) associating with in-plane lattice vibration, a shoulder peak D′ (~ 1620 cm⁻¹) which signifies the presence of defects within the graphitic carbon–carbon structure, and second-order peaks of 2D (~ 2700 cm⁻¹) and 2D′ (~ 3240 cm⁻¹) [227, 228]. The absence of the D-band, which denotes the sp³ hybridization, is a common characteristic in chemically vapor deposition-grown or mechanically exfoliated graphene sheets due to the near-flawless nature of the graphitic structure with little defect [170].

The principles underlying Polarized Raman spectroscopy for assessing graphene alignment stem from the intricate interplay between incident light and the lattice structure of graphene, coupled with the resulting vibrational modes [222]. The intensity of Raman signals from graphene is notably influenced by the angle of polarization, demonstrating a robust Raman resonance along the alignment direction parallel to the polarization vector [229]. Polarized Raman spectroscopy enables the excitation of diverse polarization modes of incident light, encompassing those that are parallel (longitudinal) and perpendicular (transverse) to the alignment direction. The interplay between the light polarization and the oriented graphene lattice significantly influences the Raman scattering efficiency, leading to discernible changes in the Raman spectrum. By assessing the Raman signal under various polarization configurations, researchers can extract valuable information about the alignment direction and assess the extent of alignment. Notably, the G-band within the Raman spectrum of graphene serves as a pivotal marker, resonating with the in-plane vibrational motion of carbon atoms in the hexagonal lattice. As graphene sheets align, distinct alterations in the characteristics of the G-band peak can occur, thereby providing valuable information about the alignment state [180]. As an example, the alignment of graphene sheets in their polymer-based composites was qualitatively investigated by Kim and coworkers using polarized Raman spectroscopy [181, 222]. The Raman spectra acquired along different directions showed slight differences in composites characterized by randomly dispersed graphene, as shown in Fig. 18b, c. However, significantly higher G-band intensities were observed when the incident laser aligned with the preferred orientation compared to the configuration perpendicular to the alignment (Fig. 18d, e).

Polarized Raman spectroscopy is also an effective tool for the quantitative assessment of graphene's spatial orientation, as shown in Fig. 18f–m. In Fig. 18f, a Cartesian coordinate system is established, with the X, Y, and Z axes correspondingly defined with respect to the specimen [230]. The laser beam operates along the Z-axis (perpendicular to the specimen's top surface) as well as the X and Y axes (parallel to the surface). Employing fixed polarization configurations, spectra are commonly acquired by systematically rotating specimens to various angles, namely Φ_X, Φ_Y, and Φ_Z, to align the laser beams parallel to the corresponding axis. The local direction of graphene sheets within a specimen is defined by denoting the surface normal vector as the z direction and the surface as xy plane, as shown in Fig. 18g [231]. The interrelation between the sample coordinates (X, Y, Z) and the graphene coordinates (x, y, z) is articulated through the Euler angles (θ, φ, ξ), where θ and φ represent the polar angles of the graphene surface normal vector in the sample Cartesian coordinates, and ξ designates the rotation angle of graphene. Illustrating the laboratory coordinates, Fig. 18h elucidates the manner in which specimens are systematically rotated by an angle Φ concerning the laser polarization directions [231].

The presented Fig. 18i, j showcases typical three-dimensional polarized Raman spectra of graphene composites, acquired across various θ values ranging from 0 to 360° in both VV and VH configurations [31]. The G-band intensity within the VV configuration displays cyclic fluctuations, exhibiting peaks and valleys every 90°, while this periodic trend is less discernible within the VH configuration. Consequently, to assess graphene's orientation, it becomes feasible to scrutinize intensities within a representative span of 0–90°, as shown in Fig. 18k. By using the G-band intensity at θ = 0° in the VV configuration as a baseline, the relative Raman intensity (I_R) of the G-band within the VV configuration demonstrates a marked reduction as θ increases, signifying a prevalent alignment of graphene in composites along the direction of θ = 0° [31]. In contrast, the relative G-band intensity within the VH showed slight variations against θ, suggesting the absence of preferential orientation.

In cases where the orientation of graphene sheets uniformly changes across a shared plane, the orientation distribution function can be expressed as f_N(θ) [230]:

$${f}_{N}\left(\theta \right)=\sum_{i=0}^{\infty }\frac{2i+1}{2}\langle {P}_{i}\left(cos\theta \right)\rangle {P}_{i}\left(cos\theta \right)$$

(8)

where P_i(cosθ) represents the Legendre polynomial of the degree i and $\langle {P}_{i}({\text{cos}}\theta )\rangle$ denotes the mean value which can be expressed as follows:

$$\langle {P}_{i}\left(cos\theta \right)\rangle =\frac{\int_{\theta =0}^{\theta =\pi }{P}_{i}\left(cos\theta \right){f}_{N}\left(\theta \right)sin\theta d\theta }{\int_{\theta =0}^{\theta =\pi }{f}_{N}\left(\theta \right)sin\theta d\theta }$$

(9)

The Raman scattering intensity of the sample, I_sample(Φ), can be determined by the polarization angle Φ in relation to the specimen. This is under the premise of a uniform distribution of the surface normal vectors around the Z-axis:

$${I}_{{\text{sample}}}\left(\Phi \right)={I}_{0}\left\{\frac{8}{15}+\langle {P}_{2}\left(cos\theta \right)\rangle \left(-\frac{16}{21}+{\frac{8}{7}{\text{cos}}}^{2}\Phi \right)+\langle {P}_{4}\left(cos\theta \right)\rangle \left(\frac{8}{35}-\frac{8}{7}{{\text{cos}}}^{2}\Phi {+{\text{cos}}}^{4}\Phi \right)\right\}$$

(10)

where I₀ is the amplitude of incident light.For graphene, a non-polar material, the $\langle {P}_{i}({\text{cos}}\theta )\rangle$ is nonzero only for even I and the polarized Raman spectroscopy can determine $\langle {P}_{2}({\text{cos}}\theta )\rangle$ and $\langle {P}_{4}({\text{cos}}\theta )\rangle$. Despite the presence of oxygen-containing groups, the crystal structure of GO and rGO remains largely similar to that of graphene, resulting in analogous vibration modes and Raman spectra [232]. Therefore, the Eq. (9) can also be extended to quantitatively analyze the spatial orientation of both GO and rGO sheets. By fitting the experimental Ramana spectra to Eq. (10), $\langle {P}_{2}({\text{cos}}\theta )\rangle$ and $\langle {P}_{4}({\text{cos}}\theta )\rangle$ values can be obtained to quantificationally describe the spatial alignment of graphene in aerogels or composites. It is worth noting that the Eq. (10) is applicable to both the G band and the 2D band of the Raman spectra of materials, yielding consistent outcomes regardless of the polarizability tensors used in the computation [231]. The $\langle {P}_{2}({\text{cos}}\theta )\rangle$ serves as the primary parameter characterizing the average orientation angle of graphene, while $\langle {P}_{4}({\text{cos}}\theta )\rangle$ holds less significance [233, 234]. Generally, larger $\langle {P}_{2}({\text{cos}}\theta )\rangle$ values indicate better alignment of graphene flakes. For instance, $\langle {P}_{2}({\text{cos}}\theta )\rangle =1$ means a perfect alignment, while $\langle {P}_{2}({\text{cos}}\theta )\rangle =(3\langle {cos}^{2}\theta \rangle -1)/2=0$ indicates randomly oriented graphene sheets, except in an extremely unique scenario where all graphene sheets are aligned along the Z axis at an angle θ that gives $\langle {{\text{cos}}}^{2}\theta \rangle =1/3$. In this case, consideration of $\langle {P}_{4}({\text{cos}}\theta )\rangle$ becomes relevant. To illustrate, a $\langle {P}_{2}({\text{cos}}\theta )\rangle$ = 0.17 and $\langle {P}_{4}({\text{cos}}\theta )\rangle$ = 0.05 is reported for graphene paper (Fig. 18l) [231], indicating a subtle long-range nanoscale ordering in graphene paper from a quantitative standpoint.

Utilizing the values of $\langle {P}_{2}({\text{cos}}\theta )\rangle$ and $\langle {P}_{4}({\text{cos}}\theta )\rangle$ values obtained using experimental polarized Raman spectra, the orientation distribution function, f_N, can be mathematically expressed as follows [235]:

$${f}_{N}\left(\theta \right)=Aexp\left[-\left({\lambda }_{2}{P}_{2}\left(cos\theta \right)+{\lambda }_{4}{P}_{4}\left(cos\theta \right)\right)\right]$$

(11)

where the coefficients A, λ₂ and λ₄ within the equation can be determined through numerical solutions [235]. A consistent f_N(θ) suggests an absence of specific orientation in the graphene structure, while it rapidly diminishes in cases of significant alignment. Applying this principle, Li et al. studied the alignment of carbon flakes in investigated the alignment of carbon flakes in materials like graphene paper and highly-ordered pyrolytic graphite (HOPG), as shown in Fig. 18m [231]. The f_N(θ) of HOPG shows a more pronounced decrease with increasing θ compared to that of graphene paper, indicating a more effective alignment of graphene sheets in HOPG. This alignment is further corroborated by SEM observations, as shown in the insets of Fig. 18m [231].

4.3 X-ray Scattering

The X-ray scattering embodies the phenomenon arising from the interaction of X-ray photons with matter, giving rise to the scattering of these photons (Fig. 19a, b) [236, 237]. This process finds its explanation in two fundamental mechanisms: elastic scattering (Rayleigh scattering) and inelastic scattering (Compton scattering and X-ray fluorescence). Elastic scattering, also known as Rayleigh scattering, occurs when X-ray photons interact with the electrons of the atoms in the material without transferring any energy to them. This type of scattering preserves the energy and wavelength of the incident X-rays, but changes their direction. In the realm of elastic X-ray scattering, two distinct techniques stand out: small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The SAXS examines the scattering of X-rays at small angles (typically 0.1° to 10°) and offers insights into the nanoscale structure, including particle size, shape, and molecular arrangement. WAXS focuses on the scattering of X-rays at larger angles (generally larger than 10°) and provides detailed information about the atomic and molecular arrangement in crystalline materials [238]. The X-rays are scattered in all directions due to the presence of nano structures, resulting in a scattered X-ray pattern. This pattern, a consequence of the interference between scattered X-rays, engenders constructive and destructive interference, thus generating a diffraction pattern amenable to excavate valuable insights regarding the dimensions, geometry, and layout of nanoscale structures within the material [239].

In the case of graphene, SAXS is effective in deciphering the alignment of graphene sheets within the material. By analyzing the scattering patterns at small angles, SAXS can reveal the degree of ordering and orientation of graphene sheets, indicating the presence of aligned structures [240, 241]. Although graphene is not a traditional crystal, it possesses a highly ordered arrangement of carbon atoms within its two-dimensional lattice. On the other hand, WAXS can provide information about the crystal structure, lattice parameters, and interatomic distances in graphene. By examining the scattering patterns at wider angles, WAXS can reveal the orientation and alignment of graphene layers, providing insights into the crystallographic phases and orientation of graphene-based materials [32]. Overall, SAXS provides information about the overall nanoscale structure and alignment of graphene sheets, while WAXS offers insights into the atomic-level arrangement and orientation of graphene layers [241, 242]. By combining SAXS and WAXS techniques, researchers can gain a comprehensive understanding of the alignment of graphene. Considering the spot size of X-ray scattering, SAXS and WAXS provides average information of samples from macro to nano scale.

The quantitative analysis of graphene alignment is facilitated through the utilization of 2D SAXS and WAXS patterns. The extent of alignment of graphene sheets is precisely assessed by establishing a correlation between the azimuthal dependency of the scattering intensity, denoted as I(θ), and an orientational distribution coefficient, O. This correlation is achieved through the application of Hermans’ distribution function [243]:

$$O=\langle \frac{1}{2}\left(3{{\text{cos}}}^{2}\theta -1\right)\rangle$$

(12)

where θ represents azimuthal angle. The orientation distribution coefficient can be correlated with the I(θ) by:

$$\cos^{2} \theta = \frac{{\mathop \smallint \nolimits_{0}^{\pi /2} I\left( \theta \right)\cos^{2} \theta \sin \theta d\theta }}{{\mathop \smallint \nolimits_{0}^{\pi /2} I\left( \theta \right)\sin \theta d\theta }}$$

(13)

By combining Eqs. (12) and (13), the orientational distribution coefficient, O, can be quantified. The O value is ranging from 0 to 1, where O = 1 indicates a perfect alignment of graphene sheets while O = 0 corresponds to a completely random orientation [244].

Lu and coworkers effectively demonstrated the manipulation of graphene alignment through the influence of an external magnetic field, as substantiated by comprehensive SAXS characterizations [245]. At a relatively modest external magnetic field strength of 1 T, the 2D SAXS pattern showcased an elliptical diffusive configuration, while the eccentricity of this elliptical pattern progressively increased at higher field strengths, as shown in Fig. 19c. To quantify this alignment, the orientational distribution coefficient was deduced through a Gaussian approximation fitting of the scattering intensity against azimuthal angle (Fig. 19d). Remarkably, the obtained results in Fig. 19e deliver a consistent raising of the orientational distribution coefficient, evolving from 0.45 at 0.5 T to a heightened value of 0.85 at 6 T. This unequivocally underscores the magnetic field's significant contribution towards enhancing the degree of graphene alignment. To delve deeper, different alignment characteristics of graphene within composites were further investigated utilizing 2D SAXS, as shown in Fig. 19f [245]. The scattering intensity of the pristine polymer exhibited a negligible profile due to the absence of graphene constituents. Conversely, when randomly dispersed, graphene induced a distinct enhancement in scattering intensity, manifesting as a broad and isotropic halo pattern. The vertical- and planar-graphene show anisotropic equatorial and meridional scattering patterns [246], respectively. These outcomes, accompanied by comparable orientational distribution coefficients approximating 0.85, definitively confirm the specific orientations of the respective graphene entities.

The assessment of graphene alignment in materials can also be carried out through the WAXS techniques. Qian et al. reported an orientational distribution coefficient of O = 0.8 in graphene film based on 2D WAXS patterns [9]. Complementing this analytical approach, alignment visualization was further corroborated via SEM characterizations. WAXS studies have also unveiled the alignment tendencies within graphene fibers subjected to varying stretching ratios, as shown in Fig. 19g–i [32]. As the stretching ratio increased, a noticeable reduction in graphene fiber diameter was observed, coinciding with the gradual diminishment of radial wrinkles along the fiber axis (Fig. 19h). Through a comprehensive analysis of the azimuthal angle-dependent scattering intensities in WAXS patterns (Fig. 19g), orientational distribution coefficients, O, were accurately calculated. For fibers subjected to the preparation process without stretching, an O value of 0.64 was recorded (Fig. 19i). Impressively, this value notably escalated to O = 0.86 in graphene fibers characterized by a stretching ratio of 32%. This signifies the contribution of WAXS to the quantitative study of alignment of graphene.

4.4 Comparison of the Characterization Techniques

The three quantitative characterization methods are compared in Table 2. SEM image-based orientation distribution analysis, reliant on SEM images, enables the visual assessment of graphene sheet orientation and alignment. This approach, operating at the microscale, provides local insights into alignment variations within the aerogel but may lack comprehensive coverage. In contrast, polarized Raman spectroscopy, operating at the same scale, offers orientation information through the analysis of anisotropic vibrational modes in graphene layers. However, it also tends to provide localized information. On a broader scale, X-ray scattering techniques, including WAXS and SAXS, emerge as versatile tools capable of quantitatively assessing alignment, crystallinity, and spacing of graphene sheets, spanning from macroscale to nanoscale. The X-ray scattering techniques, which are more comprehensive and quantitative, are highly adaptable, offering insights into structural properties across a wide range of length scales and are thus highly valuable for studying the alignment degree in graphene aerogels in academic research endeavors.

Table 2 Comparisons of different quantitative characterization techniques of the alignment degree

Full size table

5 Multifunctional Applications

5.1 Energy Conersion and Storage

5.1.1 Solar-Thermal Energy Conversion

Solar-thermal energy conversion and storage harness renewable solar energy, addressing temporal, intensity, and spatial discrepancies between thermal energy demand and supply, and offering a potent means for solar energy utilization. Solar-thermal materials absorb energy from sunlight, raising temperatures during light exposure, and release energy gradually upon cessation, thus achieving effective energy storage and release (Fig. 20a) [261]. Copyright 2020, Elsevier. c, d Thermally annealed aligned graphene aerogel for Li-batteries to hinder the growth of dendrite. Reproduced with permission [263]. Copyright 2021, Elsevier. e–j Comparison of the Li ion diffusion and dendrite growth in vertically aligned, horizontally aligned, and randomly arranged graphene aerogels. Reproduced with permission [265]. Copyright 2020, Elsevier

Highly aligned graphene aerogel-based composites for Li-ion batteries. a Schematic illustration of the Li-ion battery. Reproduced with permission [259].

Full size image

The development of Li-batteries faces a significant hurdle due to the uncontrollable growth of Li dendrites, originating from nonuniform plating and strip** of Li upon cycling and aggravating by unstable anode/electrolyte interphase properties electrode/electrolyte interphase properties (such as complex pathways for ion transport, large gradients in Li-ion concentration, significant chemical reactivity, and variable localized current densities) [261]. Taking advantages of highly porous, ultralow-volumetric-density and aligned architecture of oriented graphene aerogel, an electrode was developed by incorporating molten Li into 3D aligned graphene aerogel [50]. This approach effectively reduced local current density, restrained dendrite formation, mitigated volume variation, and promoted the utilization of Li, all of which contributed to the development of an efficient Li metal anode, achieving a lifetime of 5000 cyclic charging and discharging under a current density of 5 mA cm⁻² in symmetric cells and a 1600-cyclic stability 2 C in full cells. The underlying mechanisms for the inhibition of dendrite growth are shown in Fig. 21c [262]. Traditionally, the nucleation of Li ions onto metallic current collectors shows inhomogeneity, leading to the aggregation of Li-ion nucleation and the subsequent non-uniform deposition of Li. As cycling progresses, this non-uniform nucleation exacerbates, resulting in the formation of dendritic structures with adverse effects, as shown by the schematic illustration of Li deposition on Cu foil in Fig. 21c. In contrast, the abundant and uniform lithophilic oxygen groups on graphene sheets obtained by controlled reduction of GO precursors provide conducive binding sites for uniform nucleation of Li ions (Fig. 21c). Additionally, the vertical microscale channels within the aligned graphene aerogel facilitate rapid transport of Li ions, fostering stable Li deposition and affording ample internal space for accommodating the expansion of the electrode at the cellular level [263]. The electrode surface retains a smooth, compact, and stable solid-electrolyte interphase (SEI), remaining free from dendritic growth over extended cycles. Consequently, stable cyclic performances (Fig. 21d), higher specific capacities with lower charge/discharge overpotentials are obtained.

The alignment contribution of graphene aerogel-based electrodes to Li batteries is further illustrated in Fig. 21e–j [264]. Distinct graphene aerogel—vertically aligned, horizontally aligned, and randomly arranged morphologies—result in different tortuosities for Li ion transmission of 1.25, 4.46, and 1.76, respectively. Larger tortuosities induce higher local current densities, leading to Li overgrowth on electrode surfaces and consequent degradation of cycling performance. The vertically aligned graphene aerogel electrode provide straight and inward channels for Li ion diffusion, allowing for highly reversible and uniform Li deposition within the internal electrode (Fig. 21e, f). Therefore, issues such as lithium overgrowth and dendrite formation are mitigated. In contrast, the tortuous randomly arranged and horizontally aligned graphene aerogel-based electrodes typically witness lithium deposition and strip** at their upper surfaces, hindering Li-ion diffusion into the internal regions and resulting in dendrite formation during cyclic performances (Fig. 21g–j). As a result, the low-tortuosity vertically aligned graphene aerogel-based electrode exhibits a Coulombic efficiency of approximately 99.1% during the high-capacity (5 mAh cm⁻²) and high-current–density (5 mA cm⁻²) charge/discharge cycles, much higher than that of the medium-tortuosity randomly arranged and the high-tortuosity horizontally aligned graphene aerogel electrodes.

5.1.3 Supercapacitor and Electrochemical Thermocell

A supercapacitor, also known as an electrochemical capacitor or ultracapacitor, is an energy storage device that utilizes electrostatic double-layer capacitance between high-specific-surface-area electrodes and electrolyte, and/or pseudocapacitance generated during fast Faradic redox reactions to store and deliver electrical energy. Electrodes with large specific surface area, high electrical conductivity, remarkable porosity, lightweight and fast ion transport capability have been considered as ideal candidates for supercapacitors. Aligned graphene aerogels deliver high electrical conductivities along the alignment, significant structural stability under compression, and porous microstructure, making them highly promising applying as electrostatic double-layer or hybrid supercapacitors (extending even to flexible/compressible supercapacitors) [255, 265, 266]. As discussed above, the vertically oriented channels in aligned graphene aerogels provide straight and fast mass transport pathways, accelerating the ion diffusion process within the electrolyte (Fig. 21f, h, j) [266]. Therefore, contributions of aligned graphene aerogel to supercapacitors can be summarized as: (i) numerous depositive sites for active materials and fast penetration of electrolytes provided by the high specific surface area of aerogels; (ii) fast ion-transmission pathways provided by the straight vertically aligned channels; and (iii) fast electron transfer provided by the interconnected framework [255, 267,268,269]. With these synergistic effects of the alignment, the performance of aligned graphene-based aerogel electrodes surpasses that of random counterparts [270], mirroring the trend observed in the discussed battery electrodes. In a supercapacitor combining the electric double-layer capacitance of graphene aerogel and the pseudocapacitance of polyaniline (PANI) show broader galvanostatic charge/discharge curves for the aligned graphene/PANI aerogel electrode than that of nonaligned one (Fig. 22a–c) [255]. The specific capacitance of all aligned graphene/PANI aerogel electrodes are much higher than those of neat PANI and the random graphene/PANI aerogel electrode (Fig. 22d).

Aligned graphene aerogels exhibit excellent structural stability under cyclic compressions, making them promising for flexible and compressible energy storage in the field of emerging wearable electronics. Batteries, particularly those with organic electrolytes like Li batteries, pose risks due to toxicity and flammability, while the advent of flexible and compressible supercapacitors has addressed these concerns. A solid-state symmetric supercapacitor constructed using bidirectionally freeze-dried graphene-based aerogels with tubular morphologies (Fig. 22e–g). The nearly symmetrical triangle shapes of this supercapacitor show good capacitive properties, delivering a good area capacitance of 109.4 mF cm⁻² at 0.4 mA cm⁻² (Fig. 22h). Owing to the super-elasticity, super-compressibility, and excellent fatigue resistance of the aligned graphene-based aerogel, this electrode exhibits a compressive supercapacitance, maintaining 88% of its original performance after 5000 cyclic compressions to 50% (Fig. 22i–k) [271]. The galvanostatic charge/discharge curves of this compressive supercapacitor expand with increasing compressive strain (Fig. 22i), suggesting enhanced supercapacitance resulted from the intact aerogel framework and better interface contact between electrolyte and electrode under compression (Fig. 22k) [271].

Aligned graphene aerogels have also exhibited their potential in high-efficiency cryo-thermocells, which offer a viable way to continuously recycle waste and low-grade heat by the conversion of temperature-relevant electrochemical redox potentials into usable electricity [272]. An anisotropic graphene aerogel consisting of holey graphene building blocks was developed by self-assembly of holey GO sheets and subsequent thermal annealing (Fig. 22l) for the construction of thermocells [273]. With interpenetrating mesopores (induced by the holes in graphene sheets) and micropores (generated by oriented microchannels), the aligned graphene aerogel delivered enhanced ion transfer through reduced ion transport path and transmission impedance, as shown in Fig. 22m, n. The disparity in the redox potential of the electrolyte between the two aligned holey graphene aerogel electrodes was prompted by the temperature gradient experienced across the cell, driving the generation of electric power [274] (Fig. 22m). An open-circuit voltage output of 2.1 V and an output power of 0.37 mW at a temperature gradient of 106 °C were achieved by 15-thermocells in series, as shown in Fig. 22o.

5.2 Super-Elasticity and Piezoresistive Sensors

The alignment in graphene aerogels and composite aerogels significantly enhances their structural stability, generating super-elasticity (the capacity to undergo large deformations and recover their original shape upon stress release), super-compressibility (the ability to endure significant compression while retaining their structural integrity), and excellent fatigue resistance (the capability to withstand and endure repetitive mechanical loading without experiencing significant degradation or failure) [266, 275].The excellent mechanical stability ensures the long-term durability and reliability of aligned graphene aerogels, making them suitable for applications where materials need to withstand cyclic loading without compromising their mechanical integrity [265].

The remarkable mechanical durability of aligned graphene-based aerogels has been elucidated through theoretical simulations and experimental assessments of both aligned and random architectures before and after compression. While these two distinct structures display similar maximum stresses during compression, the random structure exhibits comparatively less robustness and resilience [162]. In the architecture resembling plant stem-like “lamellar layers with interconnected bridges” (Fig. 23a–c) [27], stress is evenly distributed across the aligned walls, preventing stress concentration and material damage. The interconnected bridges effectively store compressive energy, leading to elastic deformation and impressive recovery. Acting as numerous “springs” between adjacent lamellar layers, these bridges foster dominant elastic deformation during compression cycles [276]. Post-compression, aerogels with highly oriented microscopic structures can almost fully revert to their original forms with minimal damage or deformation (Fig. 23c), which is also reflected by the comparable stress values during the cyclic loading (Fig. 23d) [161, 276]. Conversely, compressive loads on randomly arranged lamellae often create localized stress concentrations, resulting in skeleton cracks and monolith collapse and continuous reduction in compressive stress during the cyclic compression (Fig. 23e–h) [27, 160].

In addition to the plant stem-like structure, the incorporation of arc-shaped lamellae with preferential alignment along the lamella direction, achieved through bidirectional freeze-drying followed by structural shrinkage, also imparts exceptional mechanical stability (Fig. 23i–l) [156]. This arch-shaped cylindrical thin-shell model has the capability to endure substantial geometric deformations without undergoing yielding due to its minimal material strain, promptly restoring its original shape as well. The demonstration of graphene aerogels effectively rebounding a ball approximately 100 times heavier than the aerogels themselves showcases the remarkable structural stability of aligned graphene aerogels [94, 123, 156]. This outstanding structural stability of the highly aligned arc-lamellae structure (Fig. 23i) contributes to the rapid recovery rate of graphene aerogels upon the release of external loading, as shown in Fig. 23j.

The quantification of super-elasticity, super-compressibility, and fatigue resistance can be achieved through stress–strain curves [277]. The stress (or pressure) exhibits a linear-elastic increase during the initial compression stage, followed by a subsequent non-linear densification accompanied by a hysteresis loop (Fig. 23d) [160]. The pressure-strain loops partially overlap at different compressive strains, suggesting minimal structural damage during compression [72]. Energy dissipation reflects permanent failure of the aerogel framework, with greater dissipation (or narrower hysteresis loop) indicating more severe structural damage. When subjected to cyclic loading, highly aligned graphene-based aerogels display remarkable super-elasticity and fatigue resistance, maintaining minimal stress reduction at a maximum compression strain of 90% even after 1000 cycles of loading [276]. The compression and recovery curves coincide at zero point, indicating an excellent elasticity. With rationally designed microstructures, a near 100% height recovery after 50 cyclic compression to 90% can be achieved [123]. A 96.7% of original height is remained after 1000 compressive cycles to strains of 90% for graphene/konjac glucomannan aerogels fabricated by careful bidirectional freeze-casting [276]. The exceptional super-elasticity and robust fatigue resistance of aligned graphene aerogels are attained through the creation of a microstructure-driven hierarchical lamellar architecture containing numerous microscale sub-structures that function as elastic units, exhibiting a minimal energy loss coefficient, limited plastic deformation, and significant stress retention during cyclic compression (Fig. 23l) [156].

The exceptional properties of super-elasticity, super-compressibility, and outstanding fatigue resistance render aligned graphene and graphene-based composite aerogels suitable for piezoelectric sensor applications, where enduring mechanical stability during long-term repeated compression is crucial [76, 271, 278, 279]. These sensors find integration in various electronic systems, including artificial electronic skins, health monitoring, human activity recognition, human–machine interfaces, and wearable entertainment devices [280]. The mechanics underlying the piezo-sensitive electrical attributes of aligned graphene-based aerogels. Under compression, the electrically conductive graphene constituents within the highly porous aerogel scaffold are compacted, leading to larger-area contacts and a reduction in aerogel resistance [281, 282]. Piezoresistive sensor sensitivity hinges on the ratio of normalized resistance change (alteration in resistance relative to the original value) and strain/pressure [283]. Besides the compressive pressure-/strain- dependent resistance variation, variations in currents and capacitances can be employed for sensitivity evaluation [284, 285].

Both aligned neat graphene aerogels and graphene-based composite aerogels have been designed for piezoresistive sensing, where aerogels are electrically connected onto two electrodes with insulating polymer tapes covered outside for deformation detection. A bidirectionally freeze-dried lamellar graphene aerogels showed a high sensitivity of − 3.69 kPa⁻¹, an impressive detection limit of 0.15 Pa capable of sensing dynamic force frequency and sound vibrations, and a robust stability over 10,000 cycles [87]. Highly aligned graphene aerogels achieved by calcium ion-assisted directional freeze-casting demonstrated a linear resistance alteration with compression strain, showcasing a sensitivity of ~ 1.3 in the 0–50% range (Fig. 23m) and remarkable reversibility under cyclic compression of various strains (Fig. 23n) and frequencies (Fig. 23o) because of their superb structural stability [35]. The introduction of polymers into aligned graphene aerogels further enhanced their structural stability and piezoresistive sensing properties [27, 265, 276, 286,287,288]. Silane-crosslinked and modified graphene aerogels exhibited an ultra-high sensitivity of − 67.1 kPa⁻¹ in a low-pressure region of 0–5 kPa and a low detection limit below 30 Pa, serving as excellent pressure sensors [286]. By introducing electrically conductive nanofibers/nanotubes/MXene into aligned graphene aerogels serving as additional interconnectors and electrical conducting pathways, remarkable piezoresistive properties can be obtained [271, 279, 281, 288, 289]. For instance, an unidirectionally freeze-casted hybrid aerogel consisting of graphene, carbon nanotubes (CNTs), and cellulose nanofibers displayed exceptional properties including excellent compressibility (> 95%), remarkable elasticity (94.6% height retention over 50,000 cycles), outstanding sensitivity over compressive strain (15 within 5% strain), and a significantly low pressure detection threshold (0.875 Pa) [279]. Based on the reduced resistance under compression, aligned graphene-based aerogels can also be applied as switches, connecting circuit upon certain degree of compaction and cutoff when releasing [27, 282].

5.3 Solar Steam

The efficient utilization of abundant solar energy for purifying contaminated water and desalinating seawater through solar steam generation stands as a sustainable approach to addressing the pressing global water scarcity challenge. The rate of water evaporation is closely tied to factors like the absorption of solar light, the transformation of solar energy into higher-grade thermal and steam energy via photothermal conversion, the water uptake, and the transportation of steam through solar-thermal conversion materials [290]. Building upon these principles, graphene aerogel-based materials hold great promise as solar steam generators due to their remarkable attributes including high specific surface area, exceptional solar light absorptivity, controllable porous frameworks, and remarkable structural integrity [207, 291]. Particularly, the aligned frameworks of graphene aerogels, characterized by meticulously engineered open channels for efficient water transportation and vapor release, surpass randomly oriented aerogels in the realms of water purification and desalination [30, 292].

The construction of an interfacial solar-steam generation system aims to concentrate light-induced heat onto steam generating materials while minimizing heat loss to the surrounding water, as shown in Fig. 24a [293]. The evolution of mass over time in the graphene aerogel-based solar stream system typically exhibits a linear pattern, indicating a stable and continuous solar steaming property [121]. Channels aligned vertically within the graphene aerogel can reflect solar incidents multiply to enhance the absorption of solar light and transfer to heats for steam generation, as well as facilitate swift upward water transport to the evaporation surface [294].

In comparison to rGO film featuring bulky aligned rGO sheets and randomly oriented rGO aerogels with a certain disordered structure (rGOF-DS), the highly-aligned rGO aerogels (VA-GSM) with vertically tubular channels exhibited enhanced performance in terms of solar light absorption, steam generation, and water transport, as shown in Fig. 24b–e [30]. The rGO film was characterized by a closely layer-by-layer assembled structure that significantly hampered the diffusion of water molecules in through-the-thickness direction (Fig. 24b). The closed-pore configuration of randomly oriented rGO aerogels (rGOF-DS) increased the transport distance of steam and thereby limited the evaporation. In contrast, vertically aligned rGO aerogel (VA-GSM), distinguished by its highly vertically aligned tubular structure, provided efficient open channels for water movement and steam release [295]. Additionally, the VA-GSM exhibited high solar light absorptivity of 93%, 98% and nearly 100% for the UV, visible, and near-infrared sunlight, respectively, far surpassing the performance of both the rGO film and rGOF-DS, as shown in Fig. 24c. Synergistic effects of the open channel, efficient sunlight absorption and fast water transport contributed to outstanding solar-thermal conversion efficiency of 83.5% under 1-sun radiation and continuous water supply for the generation of steam. Consequently, VA-GSM achieved an average water evaporation rate of up to 1.57 kg m⁻² h⁻¹ under 1 sun (Fig. 24d), and a higher rate of 6.25 kg m⁻² h⁻¹ under 4 suns (Fig. 24e).

The solar steam properties of aligned graphene aerogels can be further enhanced with the incorporation of solar-absorbable material, such as MXene [296], and CNT [297]. The MXene itself is also a promising solar-steam candidate due to its near 100% light-to-heat conversion efficiency [298, 299]. Typical MXene aerogels with different morphologies, such as fibrous [300], vertically aligned Janus [301], sandwich-structured [302], cellular [303] and feather-like aerogels [304], exhibit evaporation rates in the range of 1.2–1.9 kg m⁻² h⁻¹ under 1-sun irradiation. A hybrid structure comprising slightly reduced rGO (incorporating plentiful polar oxygen-containing groups to expedite water evaporation) and MXene (offering near 100% absorption of sunlight and efficient solar-thermal conversion) achieved a water evaporation rate of 2.09 kg m⁻² h⁻¹ under 1-sun exposure and expedited the desalination of seawater, boasting ion rejection rates exceeding 99% for most ions [305]. The simultaneous presence of various water states—bound water (water molecules bonded to polar groups in rGO sheets), free water (in regions distant from hydrophilic surfaces), and intermediate water in between—reduced the vaporization enthalpy and promoted solar steam generating [305]. The rGO/MXene hybrid aerogels with a configuration of "lamellar layers with interconnected bridges" further amplified multiple reflections of lights, consequently enhancing the effective absorption of solar incidence, obtaining an even higher water evaporation rate of 2.84 kg m⁻² h⁻¹ and a 96% of energy transfer under 1-sun irradiation [306], higher than MXene aerogels [300,301,302,303,304]. Similarly, the incorporation of CNTs into graphene aerogels has demonstrated a notable improvement in solar steam generation properties [307], showing great potential to achieve higher evaporation ratio compared to aerogels containing individual CNTs [308,309,310,311].

5.4 Thermal Management

Thermally conductive graphene aerogels and their composites hold substantial promise in thermal energy conversion/storage and thermal transport applications. While their role in photothermal conversion and storage has been discussed in the preceding “solar-thermal energy conversion and solar steam” section, this segment focuses on their applications in heat transport. As previously introduced in the “Anisotropic properties” section, the thermal conductivity of highly aligned graphene aerogels and their composites exhibits anisotropy, rendering them ideal candidates for diverse thermal roles, including thermal conductors (owing to high thermal conductivity along the alignment), thermal insulators (due to low thermal conductivity transverse the alignment) or thermal regulators (with the assistance of phase change materials) based on their distinct thermal conduction attributes along different axes [118].

The establishment of pre-constructed 3D continuous networks, which effectively diminish thermal interfacial resistances between graphene and polymers, the preferred alignment enabling directional heat dissipation, and the exceptional thermal conductivity of high-quality graphene, synergistically enable efficient heat management and thermal dissipation in composites based on aligned graphene aerogels [15, 312, 313]. This makes vertically aligned graphene aerogel-based composites particularly suitable for thermal interface materials (TIMs) (Fig. 25a), where substantial thermal conductivities along the vertical direction are crucial for effectively dissipating heat from electronic devices [31, 158, 164, 312]. The air-dried, self-assembled graphene aerogel demonstrated a distinct vertical orientation of graphene building block and a substantial graphene loading of 35 wt% within epoxy composites, as shown in Fig. 25b [165]. Upon subjecting the graphene aerogel to thermal annealing, aimed at reinstating the highly thermally conductive graphitic structure within the building blocks, the thermal conductivities of aligned graphene aerogel/epoxy composites witnessed significant improvement. For composites incorporating 35 wt% (or 19 vol%) of graphene aerogel annealed at 2800 °C, thermal conductivities surged to 35.5 W m⁻¹ K⁻¹ (Fig. 25c). This remarkable enhancement reflected an efficiency increase of 884%, exhibiting its superiority over a variety of materials (Fig. 25d). Thermally conductive lamellar-structured graphene aerogel/epoxy composites were fabricated by bidirectional freeze-casting, followed by a high-temperature annealing process at 2800 °C and subsequent epoxy impregnation, with the graphene content further improved by compressing the lamellar aerogel after epoxy infiltration (Fig. 25e) [166]. This composite exhibited distinct thermal conductivities across different directions, with the highest conductivity of 20.0 W m⁻¹ K⁻¹ achieved along the vertical alignment at a graphene content of 4.28 wt% (or 2.3 vol%) (Fig. 25f), which is a striking 100 times greater than that of neat epoxy. The exceptionally high thermal conductivity at a relatively low filler loading underscores the substantial contribution of aligned graphene networks to the composite's thermal conductivity (Fig. 25g).

The anisotropic microstructures within oriented graphene and composite aerogels substantially improve the thermal conducting and dissipating efficiency along the alignment direction. This intricate arrangement effectively mitigates heat localization while reducing the heat transfer across the aligned porous channels in the transverse direction, giving composites low thermal conductivities perpendicular to the alignment [37, 78]. Building on this anisotropy, a further reduction in thermal conductivity of aligned graphene aerogels perpendicular to the alignment can be achieved by introducing scattering interfaces (such as incorporating a second component) [34, 314], and embedding hierarchical microstructures (like hollow spheres on the aerogel framework) [315]. For instance, the directionally freeze-dried rGO/polyimide (PI) composite aerogels delivered a remarkably low thermal conductivity of 0.012 W m⁻¹ K⁻¹ perpendicular to the alignment, rendering them highly promising for applications in thermal insulation, particularly in aerospace, energy-efficient buildings and wearable devices [163]. Peng et al. fabricated a hierarchical rGO/PI composite aerogel through a multi-step process including directional freeze-casting of a suspension which contained polystyrene (PS) microspheres, poly(ethylenimine) (PEI), GO sheets, and PI precursors, followed by a low-temperature thermal annealing which removed the sacrificial PS and PEI, reduced GO, and facilitated the formation of PI, as shown in Fig. 25h [37]. The elimination of PS microspheres resulted in the creation of hollow microspheres within the aligned rGO/PI frameworks (Fig. 25i), which considerably obstructed thermal transport by enhancing interfacial phonon scattering, as highlighted in the enlarged area of Fig. 25j. The integration of these hollow microspheres onto the aerogel walls significantly reduced the thermal conductivity of the rGO/PI composite aerogel when measured perpendicular to the alignment, decreasing it from 0.019 to as low as 0.009 W m⁻¹ K⁻¹ (Fig. 25k). This composite presented a notable reduction compared to conventional polymer-based thermal insulators and natural insulating materials (Fig. 25l). As a demonstration, the anisotropic thermally insulating properties of highly oriented composite aerogels can be visualized by thermographic images (Fig. 25m) [37].

Thermal insulation plays an important role in enhancing fire retardancy by impeding flame spread through the reduction of heat conduction, a pivotal mechanism for decelerating fire progression [316]. The prevention of localized overheat by thermal insulating materials significantly reduces ignition risks. The inherent advantages of graphene, with its strong sp² carbon structure, make it particularly well-suited for fire retardancy by preventing the permeation of oxygen into materials and acting as an anticorrosion and flame-retardant layer [317]. Graphene aerogels, showing the synergistic effects of their 3D porous structure's thermal insulating property and graphene's flame-retardant nature, have demonstrated promising results in fire retardancy [6, 318]. The 3D graphene frameworks effectively increase the limiting oxygen index, representing the oxygen concentration required to sustain material combustion, by impeding the oxygen and heat transfer [319], thereby enhancing the flame-retardant properties. The stability of the strong sp² carbon bonds and the capacity to confine nonflammable carbon dioxide gas within the pores imparts flame resistance to cellular graphene aerogels in air up to 1500 °C, surpassing that of graphene layers on substrates (~ 550 °C) [320]. Aligned composite aerogels, even with a low GO content of 10 wt%, exhibited notable fire retardancy, suppressing self-propagation of the flame [315]. While aligned graphene aerogels show promise in fire retardancy due to their low thermal conductivity perpendicular to the alignment direction and the significant barrier effect of the aligned walls to oxygen permeation, their full potential remains largely unexplored.

When coupled with PCMs, the aligned graphene aerogels can be applied for thermal adjustment purposes, effectively storing thermal energy at elevated temperatures and releasing it as the ambient temperature drops. These graphene aerogel/PCM composites exhibit the capacities for “energy regulation” and “energy inverse compensation,” leveraging the PCM's temperature regulation capacity [254, 321]. In an example inspired by spider webs, a graphene aerogel/PCM composite demonstrated effective thermal adjustment and management in battery systems, as illustrated in Fig. 25n, o [102]. The heat generated during battery operation was effectively transported to and stored within this phase-changing composite, thus preventing the accumulation of heat within the battery. Temperature raising in batteries during the charging and discharging process was impeded by this composite, thereby significantly decreasing potential safety risks and concurrently extending the operational lifespan of the batteries. A gradient GO aerogel/PCM composite structure with a moderate thermal conductivity of ~ 1 W m⁻¹ K⁻¹ was proved to be effective in thermal management in different environmental temperatures [252]. This composite exhibited the ability to maintain a higher skin temperature in cold environments and a lower localized surface temperature in hot environments.

5.5 Organic Absorption

Organic absorption holds paramount importance in environmental remediation, aiding in the elimination of organic pollutants from water to safeguard ecosystems and human well-being. Over the past decade, graphene aerogels have emerged as potent organic-absorbing materials for environmental restoration and water treatment due to their exceptional porosity, structural stability, chemical resilience, and absorption capabilities [122, 282]. Taking inspiration from plant stems, materials featuring aligned pores provide efficient pathways for organic solvent and oil absorption, offering a solution for effective organic uptake. Specifically, graphene and graphene-based composite aerogels designed with aligned structures are hydrophobic and organophilic (repelling water and absorbing organic liquids), thereby facilitating the separation of oil and organic solvents from water [51, 71].

Organic solvent and oil absorption hinges on capillary forces, denoted as F, created when hydrophobic capillary-like porous structures of aligned aerogels come into contact with organic liquids, as shown in Fig. 26a [36]. As per Laplace's Law, the capillary force of the liquid in tubular structure is determined by Eq. (14):

$$F=\frac{2\gamma {\text{cos}}\alpha }{r}$$

(14)

where γ represents the surface tension of the liquid–air interface, α signifies the static contact angle, and r stands for the radius of the aligned channels [36]. According to this equation, as the channel radius diminishes, the capillary force increases, suggesting that micropores and mesopores contribute to a greater driving force for organic liquid absorption while macropores serve as storage spaces [322]. This capillary effect in aligned graphene and graphene-based composite aerogels equips them with a self-driven liquid absorption capability. The self-moved height, h, to which absorbable organic liquids rise is calculated using Eq. (15) [323]:

$$h=\frac{2\gamma {\text{cos}}\alpha }{\rho gr}$$

(15)

where ρ denotes the liquid density and g represents the local gravitational acceleration. Therefore, narrower capillary leads to higher automatic absorbing height. Thus, narrower capillaries lead to greater automatic absorbing heights.

The capillarity within aligned graphene aerogels can significantly accelerate absorption rates and achieve rapid absorption within the first 3–5 s and equilibrium within 10 s [277]. In Fig. 26b, a typical absorption process involving vertically aligned graphene-based aerogels is depicted, demonstrating the absorption of ethyl acetate and carbon tetrachloride stained with Sudan red [36]. Despite their varying densities in comparison to water, both organic solvents are efficiently absorbed upon contact with the aligned aerogel within a mere 4 s.

The absorption capacity, which is the weight ratio of material before and after organic absorption, is influenced by the density and viscosity of organic liquids. A hybrid aerogel composed of directionally freeze-cast and dried graphene/cellulose nanocrystals has demonstrated remarkable and liquid-density-dependent absorption capabilities, ranging from 105 to 276 g g⁻¹, as shown in Fig. 26c [36]. A typical aligned graphene-based aerogel, structured with “lamellar layers and interconnected bridges,” showcases an absorption capacity of approximately 150 g g⁻¹ for oil/organic solvents with relatively low densities, around 210–250 g g⁻¹ for higher-density organic liquids and even up to 310 g g⁻¹ for the densest oils [277]. While aligned micro-channels among lamellae facilitate swift absorption, the bridges connecting these lamellae enhance organic liquid storage and absorption capacity [276]. The absorption rate for viscous oils increases with temperature due to reduced oil viscosity and enhanced oil movement into the aerogel channels [276].

Potential applications of aligned graphene aerogels in oil/organic absorption were explored, focusing on the continuous separation of water and organic liquids through a systematic pum** system. As shown in Fig. 26d, e, a vertically aligned graphene-based aerogel was positioned on the liquid surface, and a needle was inserted into the aerogel structure. Upon opening of the pump, the resultant pressure differential actively facilitated the segregation of oil or organic solvents from the aqueous phase, which demonstrated the feasibility of employing aligned graphene aerogels for achieving efficient and continuous separation of immiscible liquid phases [277]. Considering the advantages of aligned graphene-based aerogels in effective solar-thermal energy transfer (transferring the solar energy into thermal energy, i.e. increased temperature of aerogels), the graphene aerogel and their composites can be designed with integrated solar-thermal convention to facilitate fast oil absorption [35].

Excellent compressibility and mechanical stability of aligned graphene-based aerogels play crucial roles in their efficient oil recovery and separation, as shown in Fig. 26f–h [36]. Squeezing is a straightforward and effective technique for oil/organic solvent recovery post-absorption, involving separation followed by mechanical compression [324]. Remarkable reusability, with less than a 3% reduction in absorption capacity after 10 cycles of absorption and squeezing, was achieved with bidirectionally freeze-dried, highly compressible graphene composite aerogels [33]. Besides squeezing, burning, and distilling of the saturated graphene aerogel were also demonstrated to be suitable for the reuse of the absorbing aerogels.

Besides the separation of the incompatible system of water and oil/organic solvents, aligned graphene-based aerogels are also effective in removal of soluble organics (such as dyes) from water. The absorption of soluble organics onto graphene-based aerogels can occur via chemical absorption following the pseudo-second-order kinetic equation [94], or physical absorption following the pseudo-first-order kinetic model [71]. The elimination of dyes is primarily driven by electrostatic interactions, wherein negatively charged oxygen-containing groups in partially reduced graphene sheets engage with positively charged dye molecules. Additionally, π-π conjugation occurs between the graphite regions within graphene sheets and the benzene rings present in the dye molecules.

5.6 EMI Shielding

Electromagnetic pollutions generated by electronics are detrimental to human health and normal operation of electronic devices, making EMI shielding materials essential to manage and mitigate the adverse effects of electromagnetic waves. Highly porous graphene aerogels and their composites hold promises in EMI shielding, thanks to their decent electrical conductivities, low mass densities and tunable microstructures [34, 325]. Regulating the phase structure of framework walls and adjusting microstructures of aerogels are two effective methodologies to enhance EMI shielding capabilities of graphene aerogel [326].

The aligned graphene building blocks in anisotropic graphene aerogels and composites contribute to enhanced EMI shielding properties by synergistic effects of several aspects [29]. (i) The anisotropic microstructure of oriented graphene aerogels and composites increases electrical conductivities along the aligning direction, favoring electrical-conductivity-dependent interaction between incident radiations and conductive aerogel walls and thus increasing reflection- and adsorption-induced EMI SEs [171, 172]. (ii) Interacting with the larger effective surface area of cell walls in transversely aligned graphene aerogels undergo multiple wave reflections, enhancing EMI shielding [327, 328]. (iii) The interaction between graphene aerogels (or their composites) and incident electromagnetic radiations introduces dynamic polarization/relaxation in highly directional structures, which causes collective macroscopic arrangement of dipoles and further improves the attenuation of waves [82, 326, 329].

Based on these mechanisms, Zhao et al. developed MXene/graphene/epoxy composites by infiltrating epoxy into the aligned MXene/graphene aerogel, showing a total EMI SE of 56.4 dB for composites with a filler content of 0.74 vol% and a 2 mm thickness [330]. Similarly, a graphene/MXene/Ni composite exhibited substantial wave absorption of 99.999996%, corresponding to a reflection loss of − 72.5 dB at a 2.15 mm thickness [331]. An EMI shielding SE of 112.2 dB, an implication of ~ 99.9999999994% blocked incident radiation, and a specific SE divided by the thickness of 173,243 dB cm² g⁻¹ were achieved by graphene aerogels prepared via chemical and thermal expansion of GO films [275]. These advancements all demonstrate the potential aligned graphene-based aerogels for EMI shielding applications. the anisotropic EMI shielding capabilities of highly aligned graphene aerogels enable the transition between EMI shielding (perpendicular to the alignment) and transmission (along the alignment), expanding their potential applications in various industries, such as wireless communication devices and aerospace.

6 Conclusions and Perspectives

In conclusion, this review highlights the recent advances in highly aligned graphene aerogels and their composites, emphasizing their unique structural characteristics, characterizations, properties, and potential applications. With the assistance of directional freeze casting technique, the self-assembly of GO LC precursors and the mechanical shearing, graphene aerogels with highly oriented walls and porous channels are fabricated. The alignment of graphene building blocks can be characterized both qualitatively and quantitatively using SEM observation, orientation distribution analysis of SEM images, Polarized Raman spectroscopy and X-ray scattering. Aligned graphene aerogels take full advantages of the remarkable in-plane mechanical, electrical, and thermal properties of the 2D graphene sheets, showing anisotropic characteristics in mechanical, electrical, thermal transport and EMI shielding properties (better performances along one particular direction at the sacrifice of transverse directions). Super-elasticity, super-compressibility and fatigue resistance are endowed by the aligned scaffolds, making aligned graphene aerogels ideal for piezoelectric sensing of pressure and compressive strain. The anisotropic thermal conductivities of graphene aerogels and their composites make them possible in various thermal-related applications, such as solar thermal energy transfer/storage, solar steam, thermal conductors, and thermal insulators. The capillary effect of oriented porous channels in highly aligned graphene-based aerogels makes them promising in organic solvent/oil absorption. Besides, they also exhibit advantages in applications like electrochemical devices and EMI shielding. The main challenges and possible solutions are proposed as follows:

(i)
One of the primary challenges in the field of highly aligned graphene aerogels is the development of scalable, controllable, and cost-effective fabrication techniques that can reliably achieve and maintain the desired level of alignment. While there have been significant advancements in the fabrication of aligned structures, many existing techniques are limited in terms of scalability and cost-efficiency, hindering their practical implementation on a larger scale. Continuous research efforts focusing on the optimization of fabrication process and the exploration of innovation approaches such as multi-step processes or hybrid techniques that combine different alignment methods are contributive. Implementing robotic systems and automated quality control for precise handling, alignment, and assembly processes can also enhance efficiency, reduce labor costs, and improve reproducibility.
(ii)
GO suspensions are currently used as precursors for the fabrication of graphene aerogels, but reduction process that often involves harsh chemical treatments or high-temperature annealing is necessary for partial restoration of the exceptional graphene properties. This limits the overall quality and large-scale fabrication of graphene aerogel-based products. Develo** high-quality, large-size graphene as building blocks and effective functionalization techniques to ensure good dispersity and compatibility hold significant promise for advancing the aligned graphene aerogels. Advancements in refining exfoliation parameters to minimize defects, maximize lateral sizes and better control over the number of layers may obtain graphene sheets with desired properties. Selectively functionalizing specific regions of graphene sheets with chemical groups or functional moieties (for example, functionalized graphene edges and well-crystalline planes) can improve dispersibility, stability, and compatibility of graphene with various matrices while maintaining the excellent intrinsic properties of graphene at a highest level, benefiting to further enhancement of aligned graphene aerogel-based materials.
(iii)
Integrating multifunctionalities of highly aligned graphene aerogel-based materials by integrating multifunctionalities to produce all-in-one devices is one of the effective ways to promote their practical applications. By combining multiple functionalities within a single material or device, a wide range of applications can be addressed more efficiently and effectively. The unique properties of highly aligned graphene aerogels, such as their high surface area, excellent mechanical strength, anisotropic thermal conductivity, and electrical properties, make them ideal candidates for multifunctional integration. For example, integration of sensing and actuation functionalities within the aligned graphene aerogel-based materials. By incorporating sensing elements into the aerogel structure, it can be used for strain or pressure sensing applications. Furthermore, the excellent mechanical properties of aligned graphene aerogels enable them to function as actuator materials in response to external stimuli, such as temperature or humidity changes. These multifunctional materials can find applications in smart structures, robotics, and wearable devices.

Abbreviations

3D:: Three-dimensional
CNT:: Carbon nanotube
CVD:: Chemical vapor deposition
EMI:: Electromagnetic interference
FWHM:: Full width at half maximum
GF:: Graphene foam
GNP:: Graphene nanoplatelet
GO:: Graphene oxide
GRGC:: Gradient reduced graphene oxide aerogel-based bilayer phase change material composite
GWF:: Graphene woven fabric
HOPG:: Highly-ordered pyrolytic graphite
KOH:: Potassium hydroxide
LC:: Liquid crystal
LGO:: Large graphene oxide
MGW:: Multilayer graphene web
MXene:: Transition metal carbides and nitrides
PANI:: Polyaniline
PCM:: Phase change material
PDMS:: Polydimethylsiloxane
PEI:: Poly(ethylenimine)
PI:: Polyimide
PS:: Polystyrene
rGO:: Reduced graphene oxide
rGOF-DS:: Reduced graphene oxide aerogels with a certain disordered structure
SAXS:: Small-angle X-ray scattering
SE:: Shielding effectiveness
SEI:: Solid-electrolyte interphase
SEM:: Scanning electron microscopic
SGO:: Small graphene oxide
TIM:: Thermal interface material
UV:: Ultraviolet
VA-GSM:: Vertically aligned reduced graphene oxide aerogels
WAXS:: Wide-angle X-ray scattering

References

C. Zhu, T.Y.-J. Han, E.B. Duoss, A.M. Golobic, J.D. Kuntz et al., Highly compressible 3D periodic graphene aerogel microlattices. Nat. Commun. 6, 6962 (2015). https://doi.org/10.1038/ncomms7962
Article CAS PubMed ADS Google Scholar
M.A. Worsley, P.J. Pauzauskie, T.Y. Olson, J. Biener, J.H. Satcher Jr. et al., Synthesis of graphene aerogel with high electrical conductivity. J. Am. Chem. Soc. 132(40), 14067–14069 (2010). https://doi.org/10.1021/ja1072299
Article CAS PubMed Google Scholar
Y. Lin, J. Chen, S. Dong, G. Wu, P. Jiang et al., Wet-resilient graphene aerogel for thermal conductivity enhancement in polymer nanocomposites. J. Mater. Sci. Technol. 83, 219–227 (2021). https://doi.org/10.1016/j.jmst.2020.12.051
Article CAS Google Scholar
S. **, L. Wang, H. **e, W. Yu, Superhydrophilic modified elastomeric RGO aerogel based hydrated salt phase change materials for effective solar thermal conversion and storage. ACS Nano 16, 3843–3851 (2022). https://doi.org/10.1021/acsnano.1c08581
Article CAS PubMed Google Scholar
Z. Wang, X. Shen, N.M. Han, X. Liu, Y. Wu et al., Ultralow electrical percolation in graphene aerogel/epoxy composites. Chem. Mater. 28, 6731–6741 (2016). https://doi.org/10.1021/acs.chemmater.6b03206
Article CAS Google Scholar
Z. Wang, R. Wei, J. Gu, H. Liu, C. Liu et al., Ultralight, highly compressible and fire-retardant graphene aerogel with self-adjustable electromagnetic wave absorption. Carbon 139, 1126–1135 (2018). https://doi.org/10.1016/j.carbon.2018.08.014
Article CAS Google Scholar
H.-Y. Zhao, C. Shu, P. Min, C. Li, W. Deng et al., Constructing anisotropic conical graphene aerogels with concentric annular structures for highly thermally conductive phase change composites towards efficient solar–thermal–electric energy conversion. J. Mater. Chem. A 10, 22488–22499 (2022). https://doi.org/10.1039/D2TA06457J
Article CAS Google Scholar
W. Zhan, S. Yu, L. Gao, F. Wang, X. Fu et al., Bioinspired assembly of carbon nanotube into graphene aerogel with “cabbagelike” hierarchical porous structure for highly efficient organic pollutants cleanup. ACS Appl. Mater. Interfaces 10, 1093–1103 (2018). https://doi.org/10.1021/acsami.7b15322
Article CAS PubMed Google Scholar
W. Qian, H. Fu, Y. Sun, Z. Wang, H. Wu et al., Scalable assembly of high-quality graphene films via electrostatic-repulsion aligning. Adv. Mater. 34, e2206101 (2022). https://doi.org/10.1002/adma.202206101
Article CAS PubMed Google Scholar
G. Yang, X. Zhang, R. Wang, X. Liu, J. Zhang et al., Ultra-stretchable graphene aerogels at ultralow temperatures. Mater. Horiz. 10, 1865–1874 (2023). https://doi.org/10.1039/d3mh00014a
Article CAS PubMed Google Scholar
Z. Wang, X. Shen, M.A. Garakani, X. Lin, Y. Wu et al., Graphene aerogel/epoxy composites with exceptional anisotropic structure and properties. ACS Appl. Mater. Interfaces 7, 5538–5549 (2015). https://doi.org/10.1021/acsami.5b00146
Article CAS PubMed Google Scholar
M. Wu, H. Geng, Y. Hu, H. Ma, C. Yang et al., Superelastic graphene aerogel-based metamaterials. Nat. Commun. 13, 4561 (2022). https://doi.org/10.1038/s41467-022-32200-8
Article CAS PubMed PubMed Central ADS Google Scholar
Y. Zhang, L. Zhang, G. Zhang, H. Li, Naturally dried graphene-based nanocomposite aerogels with exceptional elasticity and high electrical conductivity. ACS Appl. Mater. Interfaces 10, 21565–21572 (2018). https://doi.org/10.1021/acsami.8b04689
Article CAS PubMed Google Scholar
F. Zhang, L. Guo, Y. Shi, Z. **, Y. Cheng et al., Structural engineering of graphite network for ultra-sensitive and durable strain sensors and strain-controlled switches. Chem. Eng. J. 452, 139664 (2023). https://doi.org/10.1016/j.cej.2022.139664
Article CAS Google Scholar
X. Guo, S. Cheng, B. Yan, Y. Li, R. Huang et al., Free-standing graphene aerogel with improved through-plane thermal conductivity after being annealed at high temperature. J. Colloid Interface Sci. 608, 2407–2413 (2022). https://doi.org/10.1016/j.jcis.2021.10.134
Article CAS PubMed ADS Google Scholar
X. **e, Y. Zhou, H. Bi, K. Yin, S. Wan et al., Large-range control of the microstructures and properties of three-dimensional porous graphene. Sci. Rep. 3, 2117 (2013). https://doi.org/10.1038/srep02117
Article PubMed PubMed Central ADS Google Scholar
X. Tong, W. Li, J. Li, S. Lu, B. Wang et al., In situ generation of TiO₂ in graphene aerogel and its epoxy composite for electromagnetic interference shielding performance. J. Mater. Sci. Mater. Electron. 33, 5886–5898 (2022). https://doi.org/10.1007/s10854-022-07770-4
Article CAS Google Scholar
G. Gorgolis, C. Galiotis, Graphene aerogels: a review. 2D Mater. 4, 032001 (2017). https://doi.org/10.1088/2053-1583/aa7883
Article CAS Google Scholar
Z. Wang, L. Liu, Y. Zhang, Y. Huang, J. Liu et al., A review of graphene-based materials/polymer composite aerogels. Polymers 15, 1888 (2023). https://doi.org/10.3390/polym15081888
Article CAS PubMed PubMed Central Google Scholar
G. Nassar, E. Daou, R. Najjar, M. Bassil, R. Habchi, A review on the current research on graphene-based aerogels and their applications. Carbon Trends 4, 100065 (2021). https://doi.org/10.1016/j.cartre.2021.100065
Article CAS Google Scholar
Z. Cheng, R. Wang, Y. Wang, Y. Cao, Y. Shen et al., Recent advances in graphene aerogels as absorption-dominated electromagnetic interference shielding materials. Carbon 205, 112–137 (2023). https://doi.org/10.1016/j.carbon.2023.01.032
Article CAS Google Scholar
X. Shen, J.-K. Kim, Graphene and MXene-based porous structures for multifunctional electromagnetic interference shielding. Nano Res. 16, 1387–1413 (2023). https://doi.org/10.1007/s12274-022-4938-6
Article CAS ADS Google Scholar
J. Mao, J. Iocozzia, J. Huang, K. Meng, Y. Lai et al., Graphene aerogels for efficient energy storage and conversion. Energy Environ. Sci. 11, 772–799 (2018). https://doi.org/10.1039/C7EE03031B
Article CAS Google Scholar
J. Yang, X. Shen, W. Yang, J.-K. Kim, Templating strategies for 3D-structured thermally conductive composites: recent advances and thermal energy applications. Prog. Mater. Sci. 133, 101054 (2023). https://doi.org/10.1016/j.pmatsci.2022.101054
Article CAS Google Scholar
S. Yu, X. Shen, J.-K. Kim, Beyond homogeneous dispersion: oriented conductive fillers for high κ nanocomposites. Mater. Horiz. 8, 3009–3042 (2021). https://doi.org/10.1039/d1mh00907a
Article CAS PubMed Google Scholar
X. Shen, Q. Zheng, J.-K. Kim, Rational design of two-dimensional nanofillers for polymer nanocomposites toward multifunctional applications. Prog. Mater. Sci. 115, 100708 (2021). https://doi.org/10.1016/j.pmatsci.2020.100708
Article CAS Google Scholar
M. Yang, N. Zhao, Y. Cui, W. Gao, Q. Zhao et al., Biomimetic architectured graphene aerogel with exceptional strength and resilience. ACS Nano 11, 6817–6824 (2017). https://doi.org/10.1021/acsnano.7b01815
Article CAS PubMed Google Scholar
B. Yao, J. Chen, L. Huang, Q. Zhou, G. Shi, Base-induced liquid crystals of graphene oxide for preparing elastic graphene foams with long-range ordered microstructures. Adv. Mater. 28, 1623–1629 (2016). https://doi.org/10.1002/adma.201504594
Article CAS PubMed Google Scholar
H. Guo, T. Hua, J. Qin, Q. Wu, R. Wang et al., A new strategy of 3D printing lightweight lamellar graphene aerogels for electromagnetic interference shielding and piezoresistive sensor applications. Adv. Mater. Technol. 7, 2101699 (2022). https://doi.org/10.1002/admt.202101699
Article CAS Google Scholar
P. Zhang, J. Li, L. Lv, Y. Zhao, L. Qu, Vertically aligned graphene sheets membrane for highly efficient solar thermal generation of clean water. ACS Nano 11, 5087–5093 (2017). https://doi.org/10.1021/acsnano.7b01965
Article CAS PubMed Google Scholar
Q. Liang, X. Yao, W. Wang, Y. Liu, C.P. Wong, A three-dimensional vertically aligned functionalized multilayer graphene architecture: an approach for graphene-based thermal interfacial materials. ACS Nano 5, 2392–2401 (2011). https://doi.org/10.1021/nn200181e
Article CAS PubMed Google Scholar
P. Li, Y. Liu, S. Shi, Z. Xu, W. Ma et al., Highly crystalline graphene fibers with superior strength and conductivities by plasticization spinning. Adv. Funct. Mater. 30, 2006584 (2020). https://doi.org/10.1002/adfm.202006584
Article CAS Google Scholar
H.-Y. Mi, X. **g, A.L. Politowicz, E. Chen, H.-X. Huang et al., Highly compressible ultra-light anisotropic cellulose/graphene aerogel fabricated by bidirectional freeze drying for selective oil absorption. Carbon 132, 199–209 (2018). https://doi.org/10.1016/j.carbon.2018.02.033
Article CAS Google Scholar
X. Jiang, Z. Zhao, S. Zhou, H. Zou, P. Liu, Anisotropic and lightweight carbon/graphene composite aerogels for efficient thermal insulation and electromagnetic interference shielding. ACS Appl. Mater. Interfaces 14, 45844–45852 (2022). https://doi.org/10.1021/acsami.2c13000
Article CAS PubMed Google Scholar
P. Liu, X. Li, X. Chang, P. Min, C. Shu et al., Highly anisotropic graphene aerogels fabricated by calcium ion-assisted unidirectional freezing for highly sensitive sensors and efficient cleanup of crude oil spills. Carbon 178, 301–309 (2021). https://doi.org/10.1016/j.carbon.2021.03.014
Article CAS Google Scholar
J. Dong, J. Zeng, B. Wang, Z. Cheng, J. Xu et al., Mechanically flexible carbon aerogel with wavy layers and springboard elastic supporting structure for selective oil/organic solvent recovery. ACS Appl. Mater. Interfaces 13, 15910–15924 (2021). https://doi.org/10.1021/acsami.1c02394
Article CAS PubMed Google Scholar
Q. Peng, Y. Qin, X. Zhao, X. Sun, Q. Chen et al., Superlight, mechanically flexible, thermally superinsulating, and antifrosting anisotropic nanocomposite foam based on hierarchical graphene oxide assembly. ACS Appl. Mater. Interfaces 9, 44010–44017 (2017). https://doi.org/10.1021/acsami.7b14604
Article CAS PubMed Google Scholar
W. Chang, X.-Y. Zhang, J. Qu, Z. Chen, Y.-J. Zhang et al., Freestanding Na₃V₂O₂(PO₄)₂F/graphene aerogels as high-performance cathodes of sodium-ion full batteries. ACS Appl. Mater. Interfaces 12, 41419–41428 (2020). https://doi.org/10.1021/acsami.0c11074
Article CAS PubMed Google Scholar
Y. Lin, F. Liu, G. Casano, R. Bhavsar, I.A. Kinloch et al., Pristine graphene aerogels by room-temperature freeze gelation. Adv. Mater. 28, 7993–8000 (2016). https://doi.org/10.1002/adma.201602393
Article CAS PubMed Google Scholar
J. Kim, A.P. Tiwari, M. Choi, Q. Chen, J. Lee et al., Boosting bifunctional oxygen electrocatalysis of graphitic C₃N₄ using non-covalently functionalized non-oxidized graphene aerogels as catalyst supports. J. Mater. Chem. A 10, 15689–15697 (2022). https://doi.org/10.1039/D2TA02031A
Article CAS Google Scholar
Y. Ham, V. Ri, J. Kim, Y. Yoon, J. Lee et al., Multi-redox phenazine/non-oxidized graphene/cellulose nanohybrids as ultrathick cathodes for high-energy organic batteries. Nano Res. 14, 1382–1389 (2021). https://doi.org/10.1007/s12274-020-3187-9
Article CAS ADS Google Scholar
J. Kim, N.M. Han, J. Kim, J. Lee, J.K. Kim et al., Highly conductive and fracture-resistant epoxy composite based on non-oxidized graphene flake aerogel. ACS Appl. Mater. Interfaces 10, 37507–37516 (2018). https://doi.org/10.1021/acsami.8b13415
Article CAS PubMed Google Scholar
J. Jia, C.-M. Kan, X. Lin, X. Shen, J.-K. Kim, Effects of processing and material parameters on synthesis of monolayer ultralarge graphene oxide sheets. Carbon 77, 244–254 (2014). https://doi.org/10.1016/j.carbon.2014.05.027
Article CAS Google Scholar
X. Lin, X. Shen, Q. Zheng, N. Yousefi, L. Ye et al., Fabrication of highly-aligned, conductive, and strong graphene papers using ultralarge graphene oxide sheets. ACS Nano 6, 10708–10719 (2012). https://doi.org/10.1021/nn303904z
Article CAS PubMed Google Scholar
Q. Zheng, W.H. Ip, X. Lin, N. Yousefi, K.K. Yeung et al., Transparent conductive films consisting of ultralarge graphene sheets produced by Langmuir-Blodgett assembly. ACS Nano 5, 6039–6051 (2011). https://doi.org/10.1021/nn2018683
Article CAS PubMed Google Scholar
Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk et al., Graphene and graphene oxide: synthesis, properties, and applications. Adv. Mater. 22, 3906–3924 (2010). https://doi.org/10.1002/adma.201001068
Article CAS PubMed Google Scholar
O.C. Compton, S.T. Nguyen, Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials. Small 6, 711–723 (2010). https://doi.org/10.1002/smll.200901934
Article CAS PubMed Google Scholar
D. Konios, M.M. Stylianakis, E. Stratakis, E. Kymakis, Dispersion behaviour of graphene oxide and reduced graphene oxide. J. Colloid Interface Sci. 430, 108–112 (2014). https://doi.org/10.1016/j.jcis.2014.05.033
Article CAS PubMed ADS Google Scholar
K. Erickson, R. Erni, Z. Lee, N. Alem, W. Gannett et al., Determination of the local chemical structure of graphene oxide and reduced graphene oxide. Adv. Mater. 22, 4467–4472 (2010). https://doi.org/10.1002/adma.201000732
Article CAS PubMed Google Scholar
Y. Ma, Y. Gu, Y. He, L. Wei, Y. Lian et al., Fast-charging and dendrite-free lithium metal anode enabled by partial lithiation of graphene aerogel. Nano Res. 15, 9792–9799 (2022). https://doi.org/10.1007/s12274-022-4261-2
Article CAS ADS Google Scholar
J. Hu, J. Zhu, S. Ge, C. Jiang, T. Guo et al., Biocompatible, hydrophobic and resilience graphene/chitosan composite aerogel for efficient oil–water separation. Surf. Coat. Technol. 385, 125361 (2020). https://doi.org/10.1016/j.surfcoat.2020.125361
Article CAS Google Scholar
L. Dou, X. Zhang, X. Cheng, Z. Ma, X. Wang et al., Hierarchical cellular structured ceramic nanofibrous aerogels with temperature-invariant superelasticity for thermal insulation. ACS Appl. Mater. Interfaces 11, 29056–29064 (2019). https://doi.org/10.1021/acsami.9b10018
Article CAS PubMed Google Scholar
M. Liu, Z. Yang, H. Sun, C. Lai, X. Zhao et al., A hybrid carbon aerogel with both aligned and interconnected pores as interlayer for high-performance lithium–sulfur batteries. Nano Res. 9, 3735–3746 (2016). https://doi.org/10.1007/s12274-016-1244-1
Article CAS Google Scholar
S. Wu, R.B. Ladani, J. Zhang, K. Ghorbani, X. Zhang et al., Strain sensors with adjustable sensitivity by tailoring the microstructure of graphene aerogel/PDMS nanocomposites. ACS Appl. Mater. Interfaces 8, 24853–24861 (2016). https://doi.org/10.1021/acsami.6b06012
Article CAS PubMed Google Scholar
Z. Xu, Y. Zhang, P. Li, C. Gao, Strong, conductive, lightweight, neat graphene aerogel fibers with aligned pores. ACS Nano 6, 7103–7113 (2012). https://doi.org/10.1021/nn3021772
Article CAS PubMed Google Scholar
M.-A. Shahbazi, M. Ghalkhani, H. Maleki, Directional freeze-casting: a bioinspired method to assemble multifunctional aligned porous structures for advanced applications. Adv. Eng. Mater. 22, 2000033 (2020). https://doi.org/10.1002/adem.202000033
Article CAS Google Scholar
G. Shao, D.A.H. Hanaor, X. Shen, A. Gurlo, Freeze casting: from low-dimensional building blocks to aligned porous structures-a review of novel materials, methods, and applications. Adv. Mater. 32, e1907176 (2020). https://doi.org/10.1002/adma.201907176
Article CAS PubMed Google Scholar
J.-H. Oh, J. Kim, H. Lee, Y. Kang, I.-K. Oh, Directionally antagonistic graphene oxide-polyurethane hybrid aerogel as a sound absorber. ACS Appl. Mater. Interfaces 10, 22650–22660 (2018). https://doi.org/10.1021/acsami.8b06361
Article CAS PubMed Google Scholar
C. Wang, M. Huang, R.S. Ruoff, Graphene oxide aerogel ‘ink’ at room temperature, and ordered structures by freeze casting. Carbon 183, 620–627 (2021). https://doi.org/10.1016/j.carbon.2021.07.046
Article CAS Google Scholar
J. Yang, W. Yang, W. Chen, X. Tao, An elegant coupling: freeze-casting and versatile polymer composites. Prog. Polym. Sci. 109, 101289 (2020). https://doi.org/10.1016/j.progpolymsci.2020.101289
Article CAS Google Scholar
D. Fan, X. Yang, J. Liu, P. Zhou, X. Zhang, Highly aligned graphene/biomass composite aerogels with anisotropic properties for strain sensing. Compos. Commun. 27, 100887 (2021). https://doi.org/10.1016/j.coco.2021.100887
Article Google Scholar
L. Quan, C. Wang, Y. Xu, J. Qiu, H. Zhang et al., Electromagnetic properties of graphene aerogels made by freeze-casting. Chem. Eng. J. 428, 131337 (2022). https://doi.org/10.1016/j.cej.2021.131337
Article CAS Google Scholar
X. Zhu, C. Yang, P. Wu, Z. Ma, Y. Shang et al., Precise control of versatile microstructure and properties of graphene aerogel via freezing manipulation. Nanoscale 12, 4882–4894 (2020). https://doi.org/10.1039/c9nr07861d
Article CAS PubMed Google Scholar
X.-H. Li, P. Liu, X. Li, F. An, P. Min et al., Vertically aligned, ultralight and highly compressive all-graphitized graphene aerogels for highly thermally conductive polymer composites. Carbon 140, 624–633 (2018). https://doi.org/10.1016/j.carbon.2018.09.016
Article CAS Google Scholar
N.M. Han, Z. Wang, X. Shen, Y. Wu, X. Liu et al., Graphene size-dependent multifunctional properties of unidirectional graphene aerogel/epoxy nanocomposites. ACS Appl. Mater. Interfaces 10, 6580–6592 (2018). https://doi.org/10.1021/acsami.7b19069
Article CAS PubMed Google Scholar
W. Gao, N. Zhao, W. Yao, Z. Xu, H. Bai et al., Effect of flake size on the mechanical properties of graphene aerogels prepared by freeze casting. RSC Adv. 7, 33600–33605 (2017). https://doi.org/10.1039/C7RA05557A
Article CAS ADS Google Scholar
U.G.K. Wegst, M. Schecter, A.E. Donius, P.M. Hunger, Biomaterials by freeze casting. Philos. Trans. A Math. Phys. Eng. Sci. 368, 2099–2121 (2010). https://doi.org/10.1098/rsta.2010.0014
Article CAS PubMed ADS Google Scholar
U.G.K. Wegst, H. Bai, E. Saiz, A.P. Tomsia, R.O. Ritchie, Bioinspired structural materials. Nat. Mater. 14, 23–36 (2015). https://doi.org/10.1038/nmat4089
Article CAS PubMed ADS Google Scholar
L. Estevez, A. Kelarakis, Q. Gong, E.H. Da’as, E.P. Giannelis, Multifunctional graphene/platinum/Nafion hybrids via ice templating. J. Am. Chem. Soc. 133, 6122–6125 (2011). https://doi.org/10.1021/ja200244s
Article CAS PubMed Google Scholar
J.L. Vickery, A.J. Patil, S. Mann, Fabrication of graphene–polymer nanocomposites with higher-order three-dimensional architectures. Adv. Mater. 21, 2180–2184 (2009). https://doi.org/10.1002/adma.200803606
Article CAS Google Scholar
Z. He, M. Qin, C. Han, X. Bai, Y. Wu et al., Pectin/graphene oxide aerogel with bamboo-like structure for enhanced dyes adsorption. Colloids Surf. A Physicochem. Eng. Aspects 652, 129837 (2022). https://doi.org/10.1016/j.colsurfa.2022.129837
Article CAS Google Scholar
S. Long, Y. Feng, F. He, S. He, H. Hong et al., An ultralight, supercompressible, superhydrophobic and multifunctional carbon aerogel with a specially designed structure. Carbon 158, 137–145 (2020). https://doi.org/10.1016/j.carbon.2019.11.065
Article CAS Google Scholar
V. Rodríguez-Mata, González-Domı́nguez JM, Benito AM, Maser WK, García-Bordejé E, Reduced graphene oxide aerogels with controlled continuous microchannels for environmental remediation. ACS Appl. Nano Mater. 2, 1210–1222 (2019). https://doi.org/10.1021/acsanm.8b02101
Article CAS Google Scholar
P. Min, J. Liu, X. Li, F. An, P. Liu et al., Thermally conductive phase change composites featuring anisotropic graphene aerogels for real-time and fast-charging solar-thermal energy conversion. Adv. Funct. Mater. 28, 1805365 (2018). https://doi.org/10.1002/adfm.201805365
Article CAS Google Scholar
C. Shen, J.E. Calderon, E. Barrios, M. Soliman, A. Khater et al., Anisotropic electrical conductivity in polymer derived ceramics induced by graphene aerogels. J. Mater. Chem. C 5, 11708–11716 (2017). https://doi.org/10.1039/C7TC03846A
Article CAS Google Scholar
Z. Lin, W. Jiang, Z. Chen, L. Zhong, C. Liu, Shape-memory and anisotropic carbon aerogel from biomass and graphene oxide. Molecules 26, 5715 (2021). https://doi.org/10.3390/molecules26185715
Article CAS PubMed PubMed Central Google Scholar
M. Farbod, M. Madadi Jaberi, Fabrication of graphene aerogel and graphene/carbon nanotube composite aerogel by freeze casting under ambient pressure and comparison of their properties. Fuller. Nanotub. Carbon Nanostruct. 29, 244–250 (2021). https://doi.org/10.1080/1536383x.2020.1832995
Article CAS ADS Google Scholar
Z. He, X. Li, H. Wang, F. Su, D. Wang et al., Synergistic regulation of the microstructure for multifunctional graphene aerogels by a dual template method. ACS Appl. Mater. Interfaces 14, 22544–22553 (2022). https://doi.org/10.1021/acsami.2c00525
Article CAS PubMed Google Scholar
X.-J. Yu, J. Qu, Z. Yuan, P. Min, S.-M. Hao et al., Anisotropic CoFe₂O₄@Graphene hybrid aerogels with high flux and excellent stability as building blocks for rapid catalytic degradation of organic contaminants in a flow-type setup. ACS Appl. Mater. Interfaces 11, 34222–34231 (2019). https://doi.org/10.1021/acsami.9b10287
Article CAS PubMed Google Scholar
B. Jiang, K. Liang, Z. Yang, K. Guo, F. Shaik et al., FeCoNiB@Boron-doped vertically aligned graphene arrays: a self-supported electrocatalyst for overall water splitting in a wide pH range. Electrochim. Acta 386, 138459 (2021). https://doi.org/10.1016/j.electacta.2021.138459
Article CAS Google Scholar
P. Yang, G. Tontini, J. Wang, I.A. Kinloch, S. Barg, Ice-templated hybrid graphene oxide-graphene nanoplatelet lamellar architectures: tuning mechanical and electrical properties. Nanotechnology 32, 205601 (2021). https://doi.org/10.1088/1361-6528/abdf8f
Article CAS PubMed ADS Google Scholar
S. Kang, S. Qiao, Y. Cao, Z. Hu, J. Yu et al., Compression strain-dependent tubular carbon nanofibers/graphene aerogel absorber with ultrabroad absorption band. Chem. Eng. J. 433, 133619 (2022). https://doi.org/10.1016/j.cej.2021.133619
Article CAS Google Scholar
Z. Zeng, N. Wu, W. Yang, H. Xu, Y. Liao et al., Sustainable-macromolecule-assisted preparation of cross-linked, ultralight, flexible graphene aerogel sensors toward low-frequency strain/pressure to high-frequency vibration sensing. Small 18, e2202047 (2022). https://doi.org/10.1002/smll.202202047
Article CAS PubMed Google Scholar
L. Liu, J. Zhang, G. Shi, H. Zhang, B. Wang et al., An elastic and lamellar piezoresistive graphene/MXene aerogel. J. Mater. Sci. 57, 11202–11214 (2022). https://doi.org/10.1007/s10853-022-07356-9
Article CAS ADS Google Scholar
Z. Chen, Y. Hu, H. Zhuo, L. Liu, S. **g et al., Compressible, elastic, and pressure-sensitive carbon aerogels derived from 2D titanium carbide nanosheets and bacterial cellulose for wearable sensors. Chem. Mater. 31, 3301–3312 (2019). https://doi.org/10.1021/acs.chemmater.9b00259
Article CAS Google Scholar
P. Feng, X. Wang, J. Yang, Biomimetic, highly reusable and hydrophobic graphene/polyvinyl alcohol/cellulose nanofiber aerogels as oil-removing absorbents. Polymers 14, 1077 (2022). https://doi.org/10.3390/polym14061077
Article CAS PubMed PubMed Central Google Scholar
P. Min, X. Li, P. Liu, J. Liu, X.-Q. Jia et al., Rational design of soft yet elastic lamellar graphene aerogels via bidirectional freezing for ultrasensitive pressure and bending sensors. Adv. Funct. Mater. 31, 2103703 (2021). https://doi.org/10.1002/adfm.202103703
Article CAS Google Scholar
M. Cao, S.-L. Li, J.-B. Cheng, A.-N. Zhang, Y.-Z. Wang et al., Fully bio-based, low fire-hazard and superelastic aerogel without hazardous cross-linkers for excellent thermal insulation and oil clean-up absorption. J. Hazard. Mater. 403, 123977 (2021). https://doi.org/10.1016/j.jhazmat.2020.123977
Article CAS PubMed Google Scholar
M. Wang, C. Shao, S. Zhou, J. Yang, F. Xu, Super-compressible, fatigue resistant and anisotropic carbon aerogels for piezoresistive sensors. Cellulose 25, 7329–7340 (2018). https://doi.org/10.1007/s10570-018-2080-0
Article CAS Google Scholar
Y. Dai, X. Wu, Z. Liu, H.-B. Zhang, Z.-Z. Yu, Highly sensitive, robust and anisotropic MXene aerogels for efficient broadband microwave absorption. Compos. Part B Eng. 200, 108263 (2020). https://doi.org/10.1016/j.compositesb.2020.108263
Article CAS Google Scholar
Q. Xu, X. Chang, Z. Zhu, L. Xu, X. Chen et al., Flexible pressure sensors with high pressure sensitivity and low detection limit using a unique honeycomb-designed polyimide/reduced graphene oxide composite aerogel. RSC Adv. 11, 11760–11770 (2021). https://doi.org/10.1039/D0RA10929K
Article CAS PubMed PubMed Central ADS Google Scholar
Y. Wu, Z. Wang, X. Shen, X. Liu, N.M. Han et al., Graphene/boron nitride-polyurethane microlaminates for exceptional dielectric properties and high energy densities. ACS Appl. Mater. Interfaces 10, 26641–26652 (2018). https://doi.org/10.1021/acsami.8b08031
Article CAS PubMed Google Scholar
G. Xu, M. Li, T. Wu, C. Teng, Highly compressible and anisotropic polyimide aerogels containing aramid nanofibers. React. Funct. Polym. 154, 104672 (2020). https://doi.org/10.1016/j.reactfunctpolym.2020.104672
Article CAS Google Scholar
J. Yang, Y. Chen, K. Gao, Y. Li, S. Wang et al., Biomimetic superelastic sodium alginate-based sponges with porous sandwich-like architectures. Carbohydr. Polym. 272, 118527 (2021). https://doi.org/10.1016/j.carbpol.2021.118527
Article CAS PubMed Google Scholar
H. Bai, Y. Chen, B. Delattre, A.P. Tomsia, R.O. Ritchie, Bioinspired large-scale aligned porous materials assembled with dual temperature gradients. Sci. Adv. 1, e1500849 (2015). https://doi.org/10.1126/sciadv.1500849
Article CAS PubMed PubMed Central ADS Google Scholar
K. Zhou, C. Chen, M. Lei, Q. Gao, S. Nie et al., Reduced graphene oxide-based highly sensitive pressure sensor for wearable electronics via an ordered structure and enhanced interlayer interaction mechanism. RSC Adv. 10, 2150–2159 (2020). https://doi.org/10.1039/c9ra08653f
Article CAS PubMed PubMed Central ADS Google Scholar
W. Ma, Z. Ma, Y. Cai, R. Du, Z. Xu et al., Elastic aerogel with tunable wettability for self-cleaning electronic skin. ACS Mater. Lett. 2, 1575–1582 (2020). https://doi.org/10.1021/acsmaterialslett.0c00464
Article CAS Google Scholar
W. Xu, Y. **ng, J. Liu, H. Wu, Y. Cui et al., Efficient water transport and solar steam generation via radially, hierarchically structured aerogels. ACS Nano 13, 7930–7938 (2019). https://doi.org/10.1021/acsnano.9b02331
Article CAS PubMed Google Scholar
C. Wang, X. Chen, B. Wang, M. Huang, B. Wang et al., Freeze-casting produces a graphene oxide aerogel with a radial and centrosymmetric structure. ACS Nano 12, 5816–5825 (2018). https://doi.org/10.1021/acsnano.8b01747
Article CAS PubMed Google Scholar
F. Su, J. Mok, J. McKittrick, Radial-concentric freeze casting inspired by porcupine fish spines. Ceramics 2, 161–179 (2019). https://doi.org/10.3390/ceramics2010015
Article CAS Google Scholar
L. Fan, J.-L. Li, Z. Cai, X. Wang, Creating biomimetic anisotropic architectures with co-aligned nanofibers and macrochannels by manipulating ice crystallization. ACS Nano 12, 5780–5790 (2018). https://doi.org/10.1021/acsnano.8b01648
Article CAS PubMed Google Scholar
Y. Lin, Q. Kang, H. Wei, H. Bao, P. Jiang et al., Spider web-inspired graphene skeleton-based high thermal conductivity phase change nanocomposites for battery thermal management. Nano-Micro Lett. 13, 180 (2021). https://doi.org/10.1007/s40820-021-00702-7
Article CAS ADS Google Scholar
R. Yu, Y. Shi, D. Yang, Y. Liu, J. Qu et al., Graphene oxide/chitosan aerogel microspheres with honeycomb-cobweb and radially oriented microchannel structures for broad-spectrum and rapid adsorption of water contaminants. ACS Appl. Mater. Interfaces 9, 21809–21819 (2017). https://doi.org/10.1021/acsami.7b04655
Article CAS PubMed Google Scholar
A. Ouyang, A. Cao, S. Hu, Y. Li, R. Xu et al., Polymer-coated graphene aerogel beads and supercapacitor application. ACS Appl. Mater. Interfaces 8, 11179–11187 (2016). https://doi.org/10.1021/acsami.6b01965
Article CAS PubMed Google Scholar
Y. Liu, D. Yang, Y. Shi, L. Song, R. Yu et al., Silver phosphate/graphene oxide aerogel microspheres with radially oriented microchannels for highly efficient and continuous removal of pollutants from wastewaters. ACS Sustain. Chem. Eng. 7, 11228–11240 (2019). https://doi.org/10.1021/acssuschemeng.9b00561
Article CAS Google Scholar
B. Dan, N. Behabtu, A. Martinez, J.S. Evans, D.V. Kosynkin et al., Liquid crystals of aqueous, giant graphene oxide flakes. Soft Matter 7, 11154–11159 (2011). https://doi.org/10.1039/C1SM06418E
Article CAS ADS Google Scholar
R. Narayan, J.E. Kim, J.Y. Kim, K.E. Lee, S.O. Kim, Graphene oxide liquid crystals: discovery, evolution and applications. Adv. Mater. 28, 3045–3068 (2016). https://doi.org/10.1002/adma.201505122
Article CAS PubMed Google Scholar
R. Jalili, S.H. Aboutalebi, D. Esrafilzadeh, K. Konstantinov, J.M. Razal et al., Formation and processability of liquid crystalline dispersions of graphene oxide. Mater. Horiz. 1, 87–91 (2014). https://doi.org/10.1039/C3MH00050H
Article CAS Google Scholar
K.E. Lee, J.E. Kim, U.N. Maiti, J. Lim, J.O. Hwang et al., Liquid crystal size selection of large-size graphene oxide for size-dependent N-do** and oxygen reduction catalysis. ACS Nano 8, 9073–9080 (2014). https://doi.org/10.1021/nn5024544
Article CAS PubMed Google Scholar
J.E. Kim, T.H. Han, S.H. Lee, J.Y. Kim, C.W. Ahn et al., Graphene oxide liquid crystals. Angew. Chem. Int. Ed. 50, 3043–3047 (2011). https://doi.org/10.1002/anie.201004692
Article CAS Google Scholar
S. Padmajan Sasikala, J. Lim, I.H. Kim, H.J. Jung, T. Yun et al., Graphene oxide liquid crystals: a frontier 2D soft material for graphene-based functional materials. Chem. Soc. Rev. 47, 6013–6045 (2018). https://doi.org/10.1039/C8CS00299A
Article CAS PubMed Google Scholar
Z. Xu, C. Gao, Aqueous liquid crystals of graphene oxide. ACS Nano 5, 2908–2915 (2011). https://doi.org/10.1021/nn200069w
Article CAS PubMed Google Scholar
Z. Xu, C. Gao, Graphene chiral liquid crystals and macroscopic assembled fibres. Nat. Commun. 2, 571 (2011). https://doi.org/10.1038/ncomms1583
Article CAS PubMed ADS Google Scholar
S. Thakur, N. Karak, Alternative methods and nature-based reagents for the reduction of graphene oxide: a review. Carbon 94, 224–242 (2015). https://doi.org/10.1016/j.carbon.2015.06.030
Article CAS Google Scholar
E. Garcia-Bordejé, A.M. Benito, W.K. Maser, Graphene aerogels via hydrothermal gelation of graphene oxide colloids: fine-tuning of its porous and chemical properties and catalytic applications. Adv. Colloid Interface Sci. 292, 102420 (2021). https://doi.org/10.1016/j.cis.2021.102420
Article CAS PubMed Google Scholar
X. Wu, K. Hou, J. Huang, J. Wang, S. Yang, Graphene-based cellular materials with extremely low density and high pressure sensitivity based on self-assembled graphene oxide liquid crystals. J. Mater. Chem. C 6, 8717–8725 (2018). https://doi.org/10.1039/C8TC01853G
Article CAS Google Scholar
Y. Liu, Q. Shi, C. Hou, Q. Zhang, Y. Li et al., Versatile mechanically strong and highly conductive chemically converted graphene aerogels. Carbon 125, 352–359 (2017). https://doi.org/10.1016/j.carbon.2017.09.072
Article CAS Google Scholar
J.D. Afroze, M.J. Abden, Z. Yuan, C. Wang, L. Wei et al., Core-shell structured graphene aerogels with multifunctional mechanical, thermal and electromechanical properties. Carbon 162, 365–374 (2020). https://doi.org/10.1016/j.carbon.2020.02.057
Article CAS Google Scholar
Q. Meng, H. Wan, W. Zhu, T. Duan, W. Yao, Naturally dried, double nitrogen-doped 3D graphene aerogels modified by plant extracts for multifunctional applications. ACS Sustain. Chem. Eng. 6, 1172–1181 (2018). https://doi.org/10.1021/acssuschemeng.7b03460
Article CAS Google Scholar
W. Zhan, X. Fu, F. Wang, W. Zhang, G. Bai et al., Effect of aromatic amine modified graphene aerogel on the curing kinetics and interfacial interaction of epoxy composites. J. Mater. Sci. 55, 10558–10571 (2020). https://doi.org/10.1007/s10853-020-04746-9
Article CAS ADS Google Scholar
J.-K. **ao, J.-Z. Gong, M. Dai, Y.-F. Zhang, S.-G. Wang et al., Reduced graphene oxide/Ag nanoparticle aerogel for efficient solar water evaporation. J. Alloys Compd. 930, 167404 (2023). https://doi.org/10.1016/j.jallcom.2022.167404
Article CAS Google Scholar
D. Dai, Y. Zhou, W. **ao, Z. Hao, H. Zhang et al., Multiple functional base-induced highly ordered graphene aerogels. J. Mater. Chem. C 9, 8849–8854 (2021). https://doi.org/10.1039/D1TC01985F
Article CAS Google Scholar
W. Deng, Q. Fang, H. Huang, X. Zhou, J. Ma et al., Oriented arrangement: the origin of versatility for porous graphene materials. Small 13, 1701231 (2017). https://doi.org/10.1002/smll.201701231
Article CAS Google Scholar
Y. Jiang, H. Shao, C. Li, T. Xu, Y. Zhao et al., Versatile graphene oxide putty-like material. Adv. Mater. 28, 10287–10292 (2016). https://doi.org/10.1002/adma.201603284
Article CAS PubMed Google Scholar
Z. **ong, C. Liao, W. Han, X. Wang, Mechanically tough large-area hierarchical porous graphene films for high-performance flexible supercapacitor applications. Adv. Mater. 27, 4469–4475 (2015). https://doi.org/10.1002/adma.201501983
Article CAS PubMed Google Scholar
Z. Tang, S. Shen, J. Zhuang, X. Wang, Noble-metal-promoted three-dimensional macroassembly of single-layered graphene oxide. Angew. Chem. Int. Ed. 49, 4603–4607 (2010). https://doi.org/10.1002/anie.201000270
Article CAS Google Scholar
P. Kumar, U.N. Maiti, K.E. Lee, S.O. Kim, Rheological properties of graphene oxide liquid crystal. Carbon 80, 453–461 (2014). https://doi.org/10.1016/j.carbon.2014.08.085
Article CAS Google Scholar
P. Poulin, R. Jalili, W. Neri, F. Nallet, T. Divoux et al., Superflexibility of graphene oxide. Proc. Natl. Acad. Sci. U.S.A. 113, 11088–11093 (2016). https://doi.org/10.1073/pnas.1605121113
Article CAS PubMed PubMed Central ADS Google Scholar
Y.H. Shim, H. Ahn, S. Lee, S.O. Kim, S.Y. Kim, Universal alignment of graphene oxide in suspensions and fibers. ACS Nano 15, 13453–13462 (2021). https://doi.org/10.1021/acsnano.1c03954
Article CAS PubMed Google Scholar
Y. Jiang, F. Guo, J. Zhang, Z. Xu, F. Wang et al., Aligning curved stacking bands to simultaneously strengthen and toughen lamellar materials. Mater. Horiz. 10, 556–565 (2023). https://doi.org/10.1039/d2mh01023b
Article CAS PubMed Google Scholar
Y. Jiang, F. Guo, Z. Xu, W. Gao, C. Gao, Artificial colloidal liquid metacrystals by shearing microlithography. Nat. Commun. 10, 4111 (2019). https://doi.org/10.1038/s41467-019-11941-z
Article CAS PubMed PubMed Central ADS Google Scholar
D.K. Maurya, S. Deo, D.Y. Khanukaeva, Analysis of Stokes flow of micropolar fluid through a porous cylinder. Math. Methods Appl. Sci. 44, 6647–6665 (2021). https://doi.org/10.1002/mma.7214
Article MathSciNet ADS Google Scholar
Z. Xu, C. Gao, Graphene in macroscopic order: liquid crystals and wet-spun fibers. Acc. Chem. Res. 47, 1267–1276 (2014). https://doi.org/10.1021/ar4002813
Article CAS PubMed Google Scholar
F. Wang, Y. Jiang, Y. Liu, F. Guo, W. Fang et al., Liquid crystalline 3D printing for superstrong graphene microlattices with high density. Carbon 159, 166–174 (2020). https://doi.org/10.1016/j.carbon.2019.12.039
Article CAS Google Scholar
L. He, J. Ye, M. Shuai, Z. Zhu, X. Zhou et al., Graphene oxide liquid crystals for reflective displays without polarizing optics. Nanoscale 7, 1616–1622 (2015). https://doi.org/10.1039/C4NR06008C
Article CAS PubMed ADS Google Scholar
L.C. Geonzon, M. Kobayashi, Y. Adachi, Effect of shear flow on the hydrodynamic drag force of a spherical particle near a wall evaluated using optical tweezers and microfluidics. Soft Matter 17, 7914–7920 (2021). https://doi.org/10.1039/d1sm00876e
Article CAS PubMed ADS Google Scholar
M. Cao, Z. Li, J. Lu, B. Wang, H. Lai et al., Vertical array of graphite oxide liquid crystal by microwire shearing for highly thermally conductive composites. Adv. Mater. 35, e2300077 (2023). https://doi.org/10.1002/adma.202300077
Article CAS PubMed Google Scholar
J. Ma, S. Lin, Y. Jiang, P. Li, H. Zhang et al., Digital programming graphene oxide liquid crystalline hybrid hydrogel by shearing microlithography. ACS Nano 14, 2336–2344 (2020). https://doi.org/10.1021/acsnano.9b09503
Article CAS PubMed Google Scholar
H. Geng, X. Liu, G. Shi, G. Bai, J. Ma et al., Graphene oxide restricts growth and recrystallization of ice crystals. Angew. Chem. Int. Ed. 56, 997–1001 (2017). https://doi.org/10.1002/anie.201609230
Article CAS Google Scholar
X. Zhang, P. Liu, Y. Duan, M. Jiang, J. Zhang, Graphene/cellulose nanocrystals hybrid aerogel with tunable mechanical strength and hydrophilicity fabricated by ambient pressure drying technique. RSC Adv. 7, 16467–16473 (2017). https://doi.org/10.1039/C6RA28178H
Article CAS ADS Google Scholar
F. Gong, W. Wang, H. Li, D.D. **a, Q. Dai et al., Solid waste and graphite derived solar steam generator for highly-efficient and cost-effective water purification. Appl. Energy 261, 114410 (2020). https://doi.org/10.1016/j.apenergy.2019.114410
Article CAS Google Scholar
J. Liu, Z. Khanam, S. Ahmed, T. Wang, H. Wang et al., Flexible antifreeze Zn-ion hybrid supercapacitor based on gel electrolyte with graphene electrodes. ACS Appl. Mater. Interfaces 13, 16454–16468 (2021). https://doi.org/10.1021/acsami.1c02242
Article CAS PubMed Google Scholar
C. Huang, J. Peng, Y. Cheng, Q. Zhao, Y. Du et al., Ultratough nacre-inspired epoxy–graphene composites with shape memory properties. J. Mater. Chem. A 7, 2787–2794 (2019). https://doi.org/10.1039/C8TA10725D
Article CAS Google Scholar
X. Meng, J. Yang, S. Ramakrishna, Y. Sun, Y. Dai, Gradient vertical channels within aerogels based on N-doped graphene meshes toward efficient and salt-resistant solar evaporation. ACS Sustain. Chem. Eng. 8, 4955–4965 (2020). https://doi.org/10.1021/acssuschemeng.0c00853
Article CAS Google Scholar
C.-Z. Qi, X. Wu, J. Liu, X.-J. Luo, H.-B. Zhang et al., Highly conductive calcium ion-reinforced MXene/sodium alginate aerogel meshes by direct ink writing for electromagnetic interference shielding and Joule heating. J. Mater. Sci. Technol. 135, 213–220 (2023). https://doi.org/10.1016/j.jmst.2022.06.046
Article CAS Google Scholar
Y. Jiang, Z. Xu, T. Huang, Y. Liu, F. Guo et al., Direct 3D printing of ultralight graphene oxide aerogel microlattices. Adv. Funct. Mater. 28, 1707024 (2018). https://doi.org/10.1002/adfm.201707024
Article CAS Google Scholar
X. Zhao, W. Gao, W. Yao, Y. Jiang, Z. Xu et al., Ion diffusion-directed assembly approach to ultrafast coating of graphene oxide thick multilayers. ACS Nano 11, 9663–9670 (2017). https://doi.org/10.1021/acsnano.7b03480
Article CAS PubMed Google Scholar
G. Shao, X. Shen, X. Huang, Multilevel structural design and heterointerface engineering of a host–guest binary aerogel toward multifunctional broadband microwave absorption. ACS Mater. Lett. 4, 1787–1797 (2022). https://doi.org/10.1021/acsmaterialslett.2c00634
Article CAS Google Scholar
L. Qiu, J.Z. Liu, S.L.Y. Chang, Y. Wu, D. Li, Biomimetic superelastic graphene-based cellular monoliths. Nat. Commun. 3, 1241 (2012). https://doi.org/10.1038/ncomms2251
Article CAS PubMed ADS Google Scholar
X. Huang, G. Yu, Y. Zhang, M. Zhang, G. Shao, Design of cellular structure of graphene aerogels for electromagnetic wave absorption. Chem. Eng. J. 426, 131894 (2021). https://doi.org/10.1016/j.cej.2021.131894
Article CAS Google Scholar
H. Yang, T. Zhang, M. Jiang, Y. Duan, J. Zhang, Ambient pressure dried graphene aerogels with superelasticity and multifunctionality. J. Mater. Chem. A 3, 19268–19272 (2015). https://doi.org/10.1039/C5TA06452J
Article CAS Google Scholar
Z.-L. Yu, N. Yang, L.-C. Zhou, Z.-Y. Ma, Y.-B. Zhu et al., Bioinspired polymeric woods. Sci. Adv. 4, eaat7223 (2018). https://doi.org/10.1126/sciadv.aat7223
Article CAS PubMed Google Scholar
K.C. Lai, L.Y. Lee, B.Y.Z. Hiew, S. Thangalazhy-Gopakumar, S. Gan, Environmental application of three-dimensional graphene materials as adsorbents for dyes and heavy metals: review on ice-templating method and adsorption mechanisms. J. Environ. Sci. (China) 79, 174–199 (2019). https://doi.org/10.1016/j.jes.2018.11.023
Article CAS PubMed Google Scholar
W. Gao, N. Zhao, T. Yu, J. **, A. Mao et al., High-efficiency electromagnetic interference shielding realized in nacre-mimetic graphene/polymer composite with extremely low graphene loading. Carbon 157, 570–577 (2020). https://doi.org/10.1016/j.carbon.2019.10.051
Article CAS Google Scholar
Y. Wang, B. Yao, H. Chen, H. Wang, C. Li et al., Preparation of anisotropic conductive graphene aerogel/polydimethylsiloxane composites as LEGO® modulars. Eur. Polym. J. 112, 487–492 (2019). https://doi.org/10.1016/j.eurpolymj.2019.01.036
Article CAS Google Scholar
H.-L. Gao, Y.-B. Zhu, L.-B. Mao, F.-C. Wang, X.-S. Luo et al., Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure. Nat. Commun. 7, 12920 (2016). https://doi.org/10.1038/ncomms12920
Article CAS PubMed PubMed Central ADS Google Scholar
Z. Wang, N.M. Han, Y. Wu, X. Liu, X. Shen et al., Ultrahigh dielectric constant and low loss of highly-aligned graphene aerogel/poly(vinyl alcohol) composites with insulating barriers. Carbon 123, 385–394 (2017). https://doi.org/10.1016/j.carbon.2017.07.079
Article CAS Google Scholar
F. Guo, X. Shen, J. Zhou, D. Liu, Q. Zheng et al., Highly thermally conductive dielectric nanocomposites with synergistic alignments of graphene and boron nitride nanosheets. Adv. Funct. Mater. 30, 1910826 (2020). https://doi.org/10.1002/adfm.201910826
Article CAS Google Scholar
G. Li, X. Zhang, J. Wang, J. Fang, From anisotropic graphene aerogels to electron- and photo-driven phase change composites. J. Mater. Chem. A 4, 17042–17049 (2016). https://doi.org/10.1039/C6TA07587H
Article CAS Google Scholar
G. Li, Z. Chu, X. Gong, M. **ao, Q. Dong et al., A wide-range linear and stable piezoresistive sensor based on methylcellulose-reinforced, lamellar, and wrinkled graphene aerogels. Adv. Mater. Technol. 7, 2101021 (2022). https://doi.org/10.1002/admt.202101021
Article CAS Google Scholar
N. Ni, S. Barg, E. Garcia-Tunon, F.M. Perez, M. Miranda et al., Understanding mechanical response of elastomeric graphene networks. Sci. Rep. 5, 13712 (2015). https://doi.org/10.1038/srep13712
Article PubMed PubMed Central ADS Google Scholar
T. Liu, M. Huang, X. Li, C. Wang, C.-X. Gui et al., Highly compressible anisotropic graphene aerogels fabricated by directional freezing for efficient absorption of organic liquids. Carbon 100, 456–464 (2016). https://doi.org/10.1016/j.carbon.2016.01.038
Article CAS Google Scholar
Y. Qin, Q. Peng, Y. Zhu, X. Zhao, Z. Lin et al., Lightweight, mechanically flexible and thermally superinsulating rGO/polyimide nanocomposite foam with an anisotropic microstructure. Nanoscale Adv. 1, 4895–4903 (2019). https://doi.org/10.1039/c9na00444k
Article CAS PubMed PubMed Central ADS Google Scholar
X. Zhao, W. Wu, D. Drummer, Y. Wang, S. Cui et al., SiC nanowires bridged graphene aerogels with a vertically aligned structure for highly thermal conductive epoxy resin composites and their mechanism. ACS Appl. Electron. Mater. 5, 2548–2557 (2023). https://doi.org/10.1021/acsaelm.3c00015
Article CAS Google Scholar
F. An, X. Li, P. Min, P. Liu, Z.-G. Jiang et al., Vertically aligned high-quality graphene foams for anisotropically conductive polymer composites with ultrahigh through-plane thermal conductivities. ACS Appl. Mater. Interfaces 10, 17383–17392 (2018). https://doi.org/10.1021/acsami.8b04230
Article CAS PubMed Google Scholar
P. Liu, X. Li, P. Min, X. Chang, C. Shu et al., 3D lamellar-structured graphene aerogels for thermal interface composites with high through-plane thermal conductivity and fracture toughness. Nano-Micro Lett. 13, 22 (2020). https://doi.org/10.1007/s40820-020-00548-5
Article CAS ADS Google Scholar
Y. Cui, S.I. Kundalwal, S. Kumar, Gas barrier performance of graphene/polymer nanocomposites. Carbon 98, 313–333 (2016). https://doi.org/10.1016/j.carbon.2015.11.018
Article CAS Google Scholar
X. Tang, H. Zhou, Z. Cai, D. Cheng, P. He et al., Generalized 3D printing of graphene-based mixed-dimensional hybrid aerogels. ACS Nano 12, 3502–3511 (2018). https://doi.org/10.1021/acsnano.8b00304
Article CAS PubMed Google Scholar
W.-L. Song, M.-S. Cao, M.-M. Lu, S. Bi, C.-Y. Wang et al., Flexible graphene/polymer composite films in sandwich structures for effective electromagnetic interference shielding. Carbon 66, 67–76 (2014). https://doi.org/10.1016/j.carbon.2013.08.043
Article CAS Google Scholar
Y. Wu, Z. Wang, X. Liu, X. Shen, Q. Zheng et al., Ultralight graphene foam/conductive polymer composites for exceptional electromagnetic interference shielding. ACS Appl. Mater. Interfaces 9, 9059–9069 (2017). https://doi.org/10.1021/acsami.7b01017
Article CAS PubMed Google Scholar
X.-H. Li, X. Li, K.-N. Liao, P. Min, T. Liu et al., Thermally annealed anisotropic graphene aerogels and their electrically conductive epoxy composites with excellent electromagnetic interference shielding efficiencies. ACS Appl. Mater. Interfaces 8, 33230–33239 (2016). https://doi.org/10.1021/acsami.6b12295
Article CAS PubMed Google Scholar
Z. Yu, T. Dai, S. Yuan, H. Zou, P. Liu, Electromagnetic interference shielding performance of anisotropic polyimide/graphene composite aerogels. ACS Appl. Mater. Interfaces 12, 30990–31001 (2020). https://doi.org/10.1021/acsami.0c07122
Article CAS PubMed Google Scholar
A. Motaghi, A. Hrymak, G.H. Motlagh, Electrical conductivity and percolation threshold of hybrid carbon/polymer composites. J. Appl. Polym. Sci. 132, 41744 (2015). https://doi.org/10.1002/app.41744
Article CAS Google Scholar
R. Taherian, Development of an equation to model electrical conductivity of polymer-based carbon nanocomposites. ECS J. Solid State Sci. Technol. 3, M26–M38 (2014). https://doi.org/10.1149/2.023406jss
Article CAS Google Scholar
J. Li, J.-K. Kim, Percolation threshold of conducting polymer composites containing 3D randomly distributed graphite nanoplatelets. Compos. Sci. Technol. 67, 2114–2120 (2007). https://doi.org/10.1016/j.compscitech.2006.11.010
Article CAS Google Scholar
P. Liu, Z. **, G. Katsukis, L.W. Drahushuk, S. Shimizu et al., Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit. Science 353, 364–367 (2016). https://doi.org/10.1126/science.aaf4362
Article CAS PubMed ADS Google Scholar
J. Jia, X. Sun, X. Lin, X. Shen, Y.-W. Mai et al., Exceptional electrical conductivity and fracture resistance of 3D interconnected graphene foam/epoxy composites. ACS Nano 8, 5774–5783 (2014). https://doi.org/10.1021/nn500590g
Article CAS PubMed Google Scholar
L. Qiu, D. Liu, Y. Wang, C. Cheng, K. Zhou et al., Mechanically robust, electrically conductive and stimuli-responsive binary network hydrogels enabled by superelastic graphene aerogels. Adv. Mater. 26, 3333–3337 (2014). https://doi.org/10.1002/adma.201305359
Article CAS PubMed Google Scholar
H. Hosseini, M. Kokabi, S.M. Mousavi, BC/rGO conductive nanocomposite aerogel as a strain sensor. Polymer 137, 82–96 (2018). https://doi.org/10.1016/j.polymer.2017.12.068
Article CAS Google Scholar
N. Yousefi, X. Lin, Q. Zheng, X. Shen, J.R. Pothnis et al., Simultaneous in situ reduction, self-alignment and covalent bonding in graphene oxide/epoxy composites. Carbon 59, 406–417 (2013). https://doi.org/10.1016/j.carbon.2013.03.034
Article CAS Google Scholar
N. Yousefi, M.M. Gudarzi, Q. Zheng, S.H. Aboutalebi, F. Sharif et al., Self-alignment and high electrical conductivity of ultralarge graphene oxide–polyurethane nanocomposites. J. Mater. Chem. 22, 12709–12717 (2012). https://doi.org/10.1039/C2JM30590A
Article CAS Google Scholar
A.S. Wajid, H.S. Tanvir Ahmed, S. Das, F. Irin, A.F. Jankowski et al., High-performance pristine graphene/epoxy composites with enhanced mechanical and electrical properties. Macromol. Mater. Eng. 298, 339–347 (2013). https://doi.org/10.1002/mame.201200043
Article CAS Google Scholar
J. Liang, Y. Wang, Y. Huang, Y. Ma, Z. Liu et al., Electromagnetic interference shielding of graphene/epoxy composites. Carbon 47, 922–925 (2009). https://doi.org/10.1016/j.carbon.2008.12.038
Article CAS Google Scholar
C. Gao, S. Zhang, F. Wang, B. Wen, C. Han et al., Graphene networks with low percolation threshold in ABS nanocomposites: selective localization and electrical and rheological properties. ACS Appl. Mater. Interfaces 6, 12252–12260 (2014). https://doi.org/10.1021/am501843s
Article CAS PubMed Google Scholar
D. Wang, X. Zhang, J.-W. Zha, J. Zhao, Z.-M. Dang et al., Dielectric properties of reduced graphene oxide/polypropylene composites with ultralow percolation threshold. Polymer 54, 1916–1922 (2013). https://doi.org/10.1016/j.polymer.2013.02.012
Article CAS Google Scholar
H. Pang, T. Chen, G. Zhang, B. Zeng, Z.-M. Li, An electrically conducting polymer/graphene composite with a very low percolation threshold. Mater. Lett. 64, 2226–2229 (2010). https://doi.org/10.1016/j.matlet.2010.07.001
Article CAS Google Scholar
L. Yang, Z. Wang, Y. Ji, J. Wang, G. Xue, Highly ordered 3D graphene-based polymer composite materials fabricated by “particle-constructing” method and their outstanding conductivity. Macromolecules 47, 1749–1756 (2014). https://doi.org/10.1021/ma402364r
Article CAS ADS Google Scholar
P. Wang, H. Chong, J. Zhang, H. Lu, Constructing 3D graphene networks in polymer composites for significantly improved electrical and mechanical properties. ACS Appl. Mater. Interfaces 9, 22006–22017 (2017). https://doi.org/10.1021/acsami.7b07328
Article CAS PubMed Google Scholar
D.-X. Yan, H. Pang, B. Li, R. Vajtai, L. Xu et al., Structured reduced graphene oxide/polymer composites for ultra-efficient electromagnetic interference shielding. Adv. Funct. Mater. 25, 559–566 (2015). https://doi.org/10.1002/adfm.201403809
Article CAS Google Scholar
Q. Zhang, X. Xu, H. Li, G. **ong, H. Hu et al., Mechanically robust honeycomb graphene aerogel multifunctional polymer composites. Carbon 93, 659–670 (2015). https://doi.org/10.1016/j.carbon.2015.05.102
Article CAS Google Scholar
G. Tang, Z.-G. Jiang, X. Li, H.-B. Zhang, A. Dasari et al., Three dimensional graphene aerogels and their electrically conductive composites. Carbon 77, 592–599 (2014). https://doi.org/10.1016/j.carbon.2014.05.063
Article CAS Google Scholar
Z. Fan, F. Gong, S.T. Nguyen, H.M. Duong, Advanced multifunctional graphene aerogel–Poly (methyl methacrylate) composites: experiments and modeling. Carbon 81, 396–404 (2015). https://doi.org/10.1016/j.carbon.2014.09.072
Article CAS Google Scholar
R. Ram, M. Rahaman, A. Aldalbahi, D. Khastgir, Determination of percolation threshold and electrical conductivity of polyvinylidene fluoride (PVDF)/short carbon fiber (SCF) composites: effect of SCF aspect ratio. Polym. Int. 66, 573–582 (2017). https://doi.org/10.1002/pi.5294
Article CAS Google Scholar
X. Liu, X. Sun, Z. Wang, X. Shen, Y. Wu et al., Planar porous graphene woven fabric/epoxy composites with exceptional electrical, mechanical properties, and fracture toughness. ACS Appl. Mater. Interfaces 7, 21455–21464 (2015). https://doi.org/10.1021/acsami.5b06476
Article CAS PubMed Google Scholar
X. Shen, Z. Wang, Y. Wu, X. Liu, Y.-B. He et al., A three-dimensional multilayer graphene web for polymer nanocomposites with exceptional transport properties and fracture resistance. Mater. Horiz. 5, 275–284 (2018). https://doi.org/10.1039/C7MH00984D
Article CAS Google Scholar
X.-Y. Qi, D. Yan, Z. Jiang, Y.-K. Cao, Z.-Z. Yu et al., Enhanced electrical conductivity in polystyrene nanocomposites at ultra-low graphene content. ACS Appl. Mater. Interfaces 3, 3130–3133 (2011). https://doi.org/10.1021/am200628c
Article CAS PubMed Google Scholar
X. Wang, H. Bai, Z. Yao, A. Liu, G. Shi, Electrically conductive and mechanically strong biomimetic chitosan/reduced graphene oxide composite films. J. Mater. Chem. 20, 9032–9036 (2010). https://doi.org/10.1039/C0JM01852J
Article CAS Google Scholar
F.-Y. Yuan, H.-B. Zhang, X. Li, H.-L. Ma, X.-Z. Li et al., In situ chemical reduction and functionalization of graphene oxide for electrically conductive phenol formaldehyde composites. Carbon 68, 653–661 (2014). https://doi.org/10.1016/j.carbon.2013.11.046
Article CAS Google Scholar
L. Yang, W. Weng, X. Fei, L. Pan, X. Li et al., Revealing the interrelation between hydrogen bonds and interfaces in graphene/PVA composites towards highly electrical conductivity. Chem. Eng. J. 383, 123126 (2020). https://doi.org/10.1016/j.cej.2019.123126
Article CAS Google Scholar
V.H. Pham, T.T. Dang, S.H. Hur, E.J. Kim, J.S. Chung, Highly conductive poly(methyl methacrylate) (PMMA)-reduced graphene oxide composite prepared by self-assembly of PMMA latex and graphene oxide through electrostatic interaction. ACS Appl. Mater. Interfaces 4, 2630–2636 (2012). https://doi.org/10.1021/am300297j
Article CAS PubMed Google Scholar
P. Yang, S. Ghosh, T. **a, J. Wang, M.A. Bissett et al., Joule heating and mechanical properties of epoxy/graphene based aerogel composite. Compos. Sci. Technol. 218, 109199 (2022). https://doi.org/10.1016/j.compscitech.2021.109199
Article CAS Google Scholar
C. Huang, J. Peng, S. Wan, Y. Du, S. Dou et al., Ultra-tough inverse artificial nacre based on epoxy-graphene by freeze-casting. Angew. Chem. Int. Ed. Engl. 58, 7636–7640 (2019). https://doi.org/10.1002/anie.201902410
Article CAS PubMed Google Scholar
L.-C. Tang, Y.-J. Wan, D. Yan, Y.-B. Pei, L. Zhao et al., The effect of graphene dispersion on the mechanical properties of graphene/epoxy composites. Carbon 60, 16–27 (2013). https://doi.org/10.1016/j.carbon.2013.03.050
Article CAS Google Scholar
M. Fang, Z. Zhang, J. Li, H. Zhang, H. Lu et al., Constructing hierarchically structured interphases for strong and tough epoxy nanocomposites by amine-rich graphene surfaces. J. Mater. Chem. 20, 9635–9643 (2010). https://doi.org/10.1039/C0JM01620A
Article CAS Google Scholar
S. Chandrasekaran, N. Sato, F. Tölle, R. Mülhaupt, B. Fiedler et al., Fracture toughness and failure mechanism of graphene based epoxy composites. Compos. Sci. Technol. 97, 90–99 (2014). https://doi.org/10.1016/j.compscitech.2014.03.014
Article CAS Google Scholar
L. Peng, Z. Xu, Z. Liu, Y. Guo, P. Li et al., Ultrahigh thermal conductive yet superflexible graphene films. Adv. Mater. 29, 1700589 (2017). https://doi.org/10.1002/adma.201700589
Article CAS Google Scholar
P. Liu, F. An, X. Lu, X. Li, P. Min et al., Highly thermally conductive phase change composites with excellent solar-thermal conversion efficiency and satisfactory shape stability on the basis of high-quality graphene-based aerogels. Compos. Sci. Technol. 201, 108492 (2021). https://doi.org/10.1016/j.compscitech.2020.108492
Article CAS Google Scholar
G. Lian, C.-C. Tuan, L. Li, S. Jiao, Q. Wang et al., Vertically aligned and interconnected graphene networks for high thermal conductivity of epoxy composites with ultralow loading. Chem. Mater. 28, 6096–6104 (2016). https://doi.org/10.1021/acs.chemmater.6b01595
Article CAS Google Scholar
J. Yang, E. Zhang, X. Li, Y. Zhang, J. Qu et al., Cellulose/graphene aerogel supported phase change composites with high thermal conductivity and good shape stability for thermal energy storage. Carbon 98, 50–57 (2016). https://doi.org/10.1016/j.carbon.2015.10.082
Article CAS Google Scholar
J. Yang, G.-Q. Qi, Y. Liu, R.-Y. Bao, Z.-Y. Liu et al., Hybrid graphene aerogels/phase change material composites: thermal conductivity, shape-stabilization and light-to-thermal energy storage. Carbon 100, 693–702 (2016). https://doi.org/10.1016/j.carbon.2016.01.063
Article CAS Google Scholar
K.M.F. Shahil, A.A. Balandin, Graphene-multilayer graphene nanocomposites as highly efficient thermal interface materials. Nano Lett. 12, 861–867 (2012). https://doi.org/10.1021/nl203906r
Article CAS PubMed ADS Google Scholar
X. Shen, Z. Wang, Y. Wu, X. Liu, Y.-B. He et al., Multilayer graphene enables higher efficiency in improving thermal conductivities of graphene/epoxy composites. Nano Lett. 16, 3585–3593 (2016). https://doi.org/10.1021/acs.nanolett.6b00722
Article CAS PubMed ADS Google Scholar
M. Shtein, R. Nadiv, M. Buzaglo, K. Kahil, O. Regev, Thermally conductive graphene-polymer composites: size, percolation, and synergy effects. Chem. Mater. 27, 2100–2106 (2015). https://doi.org/10.1021/cm504550e
Article CAS Google Scholar
A. Li, C. Zhang, Y.-F. Zhang, RGO/TPU composite with a segregated structure as thermal interface material. Compos. Part A Appl. Sci. Manuf. 101, 108–114 (2017). https://doi.org/10.1016/j.compositesa.2017.06.009
Article CAS Google Scholar
A. Gao, F. Zhao, F. Wang, G. Zhang, S. Zhao et al., Highly conductive and light-weight acrylonitrile-butadiene-styrene copolymer/reduced graphene nanocomposites with segregated conductive structure. Compos. Part A Appl. Sci. Manuf. 122, 1–7 (2019). https://doi.org/10.1016/j.compositesa.2019.04.019
Article CAS Google Scholar
K.H. Kim, J.U. Jang, G.Y. Yoo, S.H. Kim, M.J. Oh et al., Enhanced electrical and thermal conductivities of polymer composites with a segregated network of graphene nanoplatelets. Materials 16, 5329 (2023). https://doi.org/10.3390/ma16155329
Article CAS PubMed PubMed Central ADS Google Scholar
N. Song, D. Cao, X. Luo, Q. Wang, P. Ding et al., Highly thermally conductive polypropylene/graphene composites for thermal management. Compos. Part A Appl. Sci. Manuf. 135, 105912 (2020). https://doi.org/10.1016/j.compositesa.2020.105912
Article CAS Google Scholar
H. Ji, D.P. Sellan, M.T. Pettes, X. Kong, J. Ji et al., Enhanced thermal conductivity of phase change materials with ultrathin-graphite foams for thermal energy storage. Energy Environ. Sci. 7, 1185–1192 (2014). https://doi.org/10.1039/C3EE42573H
Article CAS Google Scholar
Q. Yan, J. Gao, D. Chen, P. Tao, L. Chen et al., A highly orientational architecture formed by covalently bonded graphene to achieve high through-plane thermal conductivity of polymer composites. Nanoscale 14, 11171–11178 (2022). https://doi.org/10.1039/d2nr02265f
Article CAS PubMed Google Scholar
J. Gong, Z. Liu, J. Yu, D. Dai, W. Dai et al., Graphene woven fabric-reinforced polyimide films with enhanced and anisotropic thermal conductivity. Compos. Part A Appl. Sci. Manuf. 87, 290–296 (2016). https://doi.org/10.1016/j.compositesa.2016.05.010
Article CAS Google Scholar
C. Shu, H.-Y. Zhao, S. Zhao, W. Deng, P. Min et al., Highly thermally conductive phase change composites with anisotropic graphene/cellulose nanofiber hybrid aerogels for efficient temperature regulation and solar-thermal-electric energy conversion applications. Compos. Part B Eng. 248, 110367 (2023). https://doi.org/10.1016/j.compositesb.2022.110367
Article CAS Google Scholar
N. Yousefi, X. Sun, X. Lin, X. Shen, J. Jia et al., Highly aligned graphene/polymer nanocomposites with excellent dielectric properties for high-performance electromagnetic interference shielding. Adv. Mater. 26, 5480–5487 (2014). https://doi.org/10.1002/adma.201305293
Article CAS PubMed Google Scholar
C.A. Bashur, L.A. Dahlgren, A.S. Goldstein, Effect of fiber diameter and orientation on fibroblast morphology and proliferation on electrospun poly(D, L-lactic-co-glycolic acid) meshes. Biomaterials 27, 5681–5688 (2006). https://doi.org/10.1016/j.biomaterials.2006.07.005
Article CAS PubMed Google Scholar
I.C. Parrag, P.W. Zandstra, K.A. Woodhouse, Fiber alignment and coculture with fibroblasts improves the differentiated phenotype of murine embryonic stem cell-derived cardiomyocytes for cardiac tissue engineering. Biotechnol. Bioeng. 109, 813–822 (2012). https://doi.org/10.1002/bit.23353
Article CAS PubMed Google Scholar
S.H. McGee, R.L. McCullough, Characterization of fiber orientation in short-fiber composites. J. Appl. Phys. 55, 1394–1403 (1984). https://doi.org/10.1063/1.333230
Article ADS Google Scholar
M. Guc, S. Levcenko, I.V. Bodnar, V. Izquierdo-Roca, X. Fontane et al., Polarized Raman scattering study of kesterite type Cu₂ZnSnS4 single crystals. Sci. Rep. 6, 19414 (2016). https://doi.org/10.1038/srep19414
Article CAS PubMed PubMed Central ADS Google Scholar
Z. Zhang, C.-S. Lee, W. Zhang, Vertically aligned graphene nanosheet arrays: synthesis, properties and applications in electrochemical energy conversion and storage. Adv. Energy Mater. 7, 1700678 (2017). https://doi.org/10.1002/aenm.201700678
Article CAS Google Scholar
Y. Wu, X. Lin, X. Shen, X. Sun, X. Liu et al., Exceptional dielectric properties of chlorine-doped graphene oxide/poly (vinylidene fluoride) nanocomposites. Carbon 89, 102–112 (2015). https://doi.org/10.1016/j.carbon.2015.02.074
Article CAS Google Scholar
K. Chu, F. Wang, X.-H. Wang, D.-J. Huang, Anisotropic mechanical properties of graphene/copper composites with aligned graphene. Mater. Sci. Eng. A 713, 269–277 (2018). https://doi.org/10.1016/j.msea.2017.12.080
Article CAS Google Scholar
Z. Li, R.J. Young, N.R. Wilson, I.A. Kinloch, C. Vallés et al., Effect of the orientation of graphene-based nanoplatelets upon the Young’s modulus of nanocomposites. Compos. Sci. Technol. 123, 125–133 (2016). https://doi.org/10.1016/j.compscitech.2015.12.005
Article CAS Google Scholar
Z. Li, R.J. Young, I.A. Kinloch, N.R. Wilson, A.J. Marsden et al., Quantitative determination of the spatial orientation of graphene by polarized Raman spectroscopy. Carbon 88, 215–224 (2015). https://doi.org/10.1016/j.carbon.2015.02.072
Article CAS Google Scholar
H. Yang, H. Hu, Z. Ni, C.K. Poh, C. Cong et al., Comparison of surface-enhanced Raman scattering on graphene oxide, reduced graphene oxide and graphene surfaces. Carbon 62, 422–429 (2013). https://doi.org/10.1016/j.carbon.2013.06.027
Article CAS Google Scholar
T. Chatterjee, C.A. Mitchell, V.G. Hadjiev, R. Krishnamoorti, Oriented single-walled carbon nanotubes–poly(ethylene oxide) nanocomposites. Macromolecules 45, 9357–9363 (2012). https://doi.org/10.1021/ma301476r
Article CAS ADS Google Scholar
R. Pérez, S. Banda, Z. Ounaies, Determination of the orientation distribution function in aligned single wall nanotube polymer nanocomposites by polarized Raman spectroscopy. J. Appl. Phys. 103, 074302 (2008). https://doi.org/10.1063/1.2885347
Article CAS ADS Google Scholar
T. Liu, S. Kumar, Quantitative characterization of SWNT orientation by polarized Raman spectroscopy. Chem. Phys. Lett. 378, 257–262 (2003). https://doi.org/10.1016/s0009-2614(03)01287-9
Article CAS ADS Google Scholar
C.-S. Tsao, E.-W. Huang, M.-H. Wen, T.-Y. Kuo, S.-L. Jeng et al., Phase transformation and precipitation of an Al–Cu alloy during non-isothermal heating studied by in situ small-angle and wide-angle scattering. J. Alloys Compd. 579, 138–146 (2013). https://doi.org/10.1016/j.jallcom.2013.04.201
Article CAS Google Scholar
S.A. Pabit, A.M. Katz, I.S. Tolokh, A. Drozdetski, N. Baker et al., Understanding nucleic acid structural changes by comparing wide-angle X-ray scattering (WAXS) experiments to molecular dynamics simulations. J. Chem. Phys. 144, 205102 (2016). https://doi.org/10.1063/1.4950814
Article CAS PubMed PubMed Central ADS Google Scholar
J. **g, Y. Chen, S. Shi, L. Yang, P. Lambin, Facile and scalable fabrication of highly thermal conductive polyethylene/graphene nanocomposites by combining solid-state shear milling and FDM 3D-printing aligning methods. Chem. Eng. J. 402, 126218 (2020). https://doi.org/10.1016/j.cej.2020.126218
Article CAS Google Scholar
S. Ansari, A. Kelarakis, L. Estevez, E.P. Giannelis, Oriented arrays of graphene in a polymer matrix by in situ reduction of graphite oxide nanosheets. Small 6, 205–209 (2010). https://doi.org/10.1002/smll.200900765
Article CAS PubMed Google Scholar
G. **n, T. Yao, H. Sun, S.M. Scott, D. Shao et al., Highly thermally conductive and mechanically strong graphene fibers. Science 349, 1083–1087 (2015). https://doi.org/10.1126/science.aaa6502
Article CAS PubMed ADS Google Scholar
Z. Xu, Y. Liu, X. Zhao, L. Peng, H. Sun et al., Ultrastiff and strong graphene fibers via full-scale synergetic defect engineering. Adv. Mater. 28, 6449–6456 (2016). https://doi.org/10.1002/adma.201506426
Article CAS PubMed Google Scholar
Y. Cheng, G. Cui, C. Liu, Z. Liu, L. Yan et al., Electric Current aligning component units during graphene fiber joule heating. Adv. Funct. Mater. 32, 2103493 (2022). https://doi.org/10.1002/adfm.202103493
Article CAS Google Scholar
J.J. Hermans, P.H. Hermans, D. Vermaas, A. Weidinger, Quantitative evaluation of orientation in cellulose fibres from the X-ray fibre diagram. Recl. Trav. Chim. Pays-Bas 65, 427–447 (1946). https://doi.org/10.1002/recl.19460650605
Article CAS Google Scholar
S. Lin, J. Tang, K. Zhang, T.S. Suzuki, Q. Wei et al., High-rate supercapacitor using magnetically aligned graphene. J. Power. Sources 482, 228995 (2021). https://doi.org/10.1016/j.jpowsour.2020.228995
Article CAS Google Scholar
X. Lu, X. Feng, J.R. Werber, C. Chu, I. Zucker et al., Enhanced antibacterial activity through the controlled alignment of graphene oxide nanosheets. Proc. Natl. Acad. Sci. U.S.A. 114, E9793–E9801 (2017). https://doi.org/10.1073/pnas.1710996114
Article CAS PubMed PubMed Central Google Scholar
L. Wu, M. Ohtani, M. Takata, A. Saeki, S. Seki et al., Magnetically induced anisotropic orientation of graphene oxide locked by in situ hydrogelation. ACS Nano 8, 4640–4649 (2014). https://doi.org/10.1021/nn5003908
Article CAS PubMed Google Scholar
X. Wang, W. Yu, L. Wang, H. **e, Vertical orientation graphene/MXene hybrid phase change materials with anisotropic properties, high enthalpy, and photothermal conversion. Sci. China Technol. Sci. 65, 882–892 (2022). https://doi.org/10.1007/s11431-021-1997-4
Article CAS ADS Google Scholar
C. Shu, H.-Y. Zhao, X.-H. Lu, P. Min, Y. Zhang et al., High-quality anisotropic graphene aerogels and their thermally conductive phase change composites for efficient solar–thermal–electrical energy conversion. ACS Sustain. Chem. Eng. 11, 11991–12003 (2023). https://doi.org/10.1021/acssuschemeng.3c02154
Article CAS Google Scholar
H. Ren, M. Tang, B. Guan, K. Wang, J. Yang et al., Hierarchical graphene foam for efficient omnidirectional solar-thermal energy conversion. Adv. Mater. 29, 1702590 (2017). https://doi.org/10.1002/adma.201702590
Article CAS Google Scholar
K.-T. Lin, H. Lin, T. Yang, B. Jia, Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion. Nat. Commun. 11, 1389 (2020). https://doi.org/10.1038/s41467-020-15116-z
Article CAS PubMed PubMed Central ADS Google Scholar
K. Sun, H. Dong, Y. Kou, H. Yang, H. Liu et al., Flexible graphene aerogel-based phase change film for solar-thermal energy conversion and storage in personal thermal management applications. Chem. Eng. J. 419, 129637 (2021). https://doi.org/10.1016/j.cej.2021.129637
Article CAS Google Scholar
Z. Luo, D. Yang, J. Liu, H.-Y. Zhao, T. Zhao et al., Nature-inspired solar-thermal gradient reduced graphene oxide aerogel-based bilayer phase change composites for self-adaptive personal thermal management. Adv. Funct. Mater. 33, 2212032 (2023). https://doi.org/10.1002/adfm.202212032
Article CAS Google Scholar
G. Qi, J. Yang, R. Bao, D. **a, M. Cao et al., Hierarchical graphene foam-based phase change materials with enhanced thermal conductivity and shape stability for efficient solar-to-thermal energy conversion and storage. Nano Res. 10, 802–813 (2017). https://doi.org/10.1007/s12274-016-1333-1
Article CAS Google Scholar
J. Feng, X. Liu, F. Lin, S. Duan, K. Zeng et al., Aligned channel Gelatin@nanoGraphite aerogel supported form-stable phase change materials for solar-thermal energy conversion and storage. Carbon 201, 756–764 (2023). https://doi.org/10.1016/j.carbon.2022.09.064
Article CAS Google Scholar
X. Wu, L. Tang, S. Zheng, Y. Huang, J. Yang et al., Hierarchical unidirectional graphene aerogel/polyaniline composite for high performance supercapacitors. J. Power. Sources 397, 189–195 (2018). https://doi.org/10.1016/j.jpowsour.2018.07.031
Article CAS ADS Google Scholar
Q. Huang, S. Ni, M. Jiao, X. Zhong, G. Zhou et al., Aligned carbon-based electrodes for fast-charging batteries: a review. Small 17, e2007676 (2021). https://doi.org/10.1002/smll.202007676
Article CAS PubMed Google Scholar
Z.P. Cano, D. Banham, S. Ye, A. Hintennach, J. Lu et al., Batteries and fuel cells for emerging electric vehicle markets. Nat. Energy 3, 279–289 (2018). https://doi.org/10.1038/s41560-018-0108-1
Article ADS Google Scholar
J.B. Goodenough, K.-S. Park, The Li-ion rechargeable battery: a perspective. J. Am. Chem. Soc. 135, 1167–1176 (2013). https://doi.org/10.1021/ja3091438
Article CAS PubMed Google Scholar
G.-L. Zhu, C.-Z. Zhao, J.-Q. Huang, C. He, J. Zhang et al., Fast charging lithium batteries: recent progress and future prospects. Small 15, e1805389 (2019). https://doi.org/10.1002/smll.201805389
Article CAS PubMed Google Scholar
K.-H. Chen, M.J. Namkoong, V. Goel, C. Yang, S. Kazemiabnavi et al., Efficient fast-charging of lithium-ion batteries enabled by laser-patterned three-dimensional graphite anode architectures. J. Power. Sources 471, 228475 (2020). https://doi.org/10.1016/j.jpowsour.2020.228475
Article CAS Google Scholar
G. Tan, L. Chong, R. Amine, J. Lu, C. Liu et al., Toward highly efficient electrocatalyst for Li-O₂ batteries using biphasic N-do** Cobalt@Graphene multiple-capsule heterostructures. Nano Lett. 17, 2959–2966 (2017). https://doi.org/10.1021/acs.nanolett.7b00207
Article CAS PubMed ADS Google Scholar
J. Zhou, M. ** by optimizing Li-ion transport and nucleation of engineered graphene aerogel. Chem. Eng. J. 427, 130967 (2022). https://doi.org/10.1016/j.cej.2021.130967
Article CAS Google Scholar
L. Dong, L. Zhang, S. Lin, Z. Chen, Y. Wang et al., Building vertically-structured, high-performance electrodes by interlayer-confined reactions in accordion-like, chemically expanded graphite. Nano Energy 70, 104482 (2020). https://doi.org/10.1016/j.nanoen.2020.104482
Article CAS Google Scholar
H. Chen, A. Pei, J. Wan, D. Lin, R. Vilá et al., Tortuosity effects in lithium-metal host anodes. Joule 4, 938–952 (2020). https://doi.org/10.1016/j.joule.2020.03.008
Article CAS Google Scholar
S. Long, Y. Feng, F. He, J. Zhao, T. Bai et al., Biomass-derived, multifunctional and wave-layered carbon aerogels toward wearable pressure sensors, supercapacitors and triboelectric nanogenerators. Nano Energy 85, 105973 (2021). https://doi.org/10.1016/j.nanoen.2021.105973
Article CAS Google Scholar
J.D. Afroze, L. Tong, M.J. Abden, Y. Chen, Multifunctional hierarchical graphene-carbon fiber hybrid aerogels for strain sensing and energy storage. Adv. Compos. Hybrid Mater. 6, 18 (2022). https://doi.org/10.1007/s42114-022-00594-0
Article CAS Google Scholar
P.-X. Li, G.-Z. Guan, X. Shi, L. Lu, Y.-C. Fan et al., Bidirectionally aligned MXene hybrid aerogels assembled with MXene nanosheets and microgels for supercapacitors. Rare Met. 42, 1249–1260 (2023). https://doi.org/10.1007/s12598-022-02189-6
Article CAS Google Scholar
Y. Zhao, Y. Alsaid, B. Yao, Y. Zhang, B. Zhang et al., Wood-inspired morphologically tunable aligned hydrogel for high-performance flexible all-solid-state supercapacitors. Adv. Funct. Mater. 30, 1909133 (2020). https://doi.org/10.1002/adfm.201909133
Article CAS Google Scholar
Y. Yoon, K. Lee, S. Kwon, S. Seo, H. Yoo et al., Vertical alignments of graphene sheets spatially and densely piled for fast ion diffusion in compact supercapacitors. ACS Nano 8, 4580–4590 (2014). https://doi.org/10.1021/nn500150j
Article CAS PubMed Google Scholar
Z. Peng, C. Yu, W. Zhong, Facile preparation of a 3D porous aligned graphene-based wall network architecture by confined self-assembly with shape memory for artificial muscle, pressure sensor, and flexible supercapacitor. ACS Appl. Mater. Interfaces 14, 17739–17753 (2022). https://doi.org/10.1021/acsami.2c00987
Article CAS PubMed Google Scholar
H. Liu, T. Xu, C. Cai, K. Liu, W. Liu et al., Multifunctional superelastic, superhydrophilic, and ultralight nanocellulose-based composite carbon aerogels for compressive supercapacitor and strain sensor. Adv. Funct. Mater. 32, 2270149 (2022). https://doi.org/10.1002/adfm.202270149
Article Google Scholar
L.E. Bell, Cooling, heating, generating power, and recovering waste heat with thermoelectric systems. Science 321, 1457–1461 (2008). https://doi.org/10.1126/science.1158899
Article CAS PubMed ADS Google Scholar
G. Li, D. Dong, G. Hong, L. Yan, X. Zhang et al., High-efficiency cryo-thermocells assembled with anisotropic holey graphene aerogel electrodes and a eutectic redox electrolyte. Adv. Mater. 31, e1901403 (2019). https://doi.org/10.1002/adma.201901403
Article CAS PubMed Google Scholar
J. Duan, B. Yu, L. Huang, B. Hu, M. Xu et al., Liquid-state thermocells: opportunities and challenges for low-grade heat harvesting. Joule 5, 768–779 (2021). https://doi.org/10.1016/j.joule.2021.02.009
Article CAS Google Scholar
E. Zhu, K. Pang, Y. Chen, S. Liu, X. Liu et al., Ultra-stable graphene aerogels for electromagnetic interference shielding. Sci. China Mater. 66, 1106–1113 (2023). https://doi.org/10.1007/s40843-022-2208-x
Article CAS Google Scholar
T. Chen, M. Li, L. Zhou, X. Ding, D. Lin et al., Bio-inspired biomass-derived carbon aerogels with superior mechanical property for oil–water separation. ACS Sustain. Chem. Eng. 8, 6458–6465 (2020). https://doi.org/10.1021/acssuschemeng.0c00910
Article CAS Google Scholar
C. Dai, W. Sun, Z. Xu, J. Liu, J. Chen et al., Assembly of ultralight dual network graphene aerogel with applications for selective oil absorption. Langmuir 36, 13698–13707 (2020). https://doi.org/10.1021/acs.langmuir.0c02664
Article CAS PubMed Google Scholar
X. Cao, J. Zhang, S. Chen, R.J. Varley, K. Pan, 1D/2D nanomaterials synergistic, compressible, and response rapidly 3D graphene aerogel for piezoresistive sensor. Adv. Funct. Mater. 30, 2003618 (2020). https://doi.org/10.1002/adfm.202003618
Article CAS Google Scholar
X. Peng, K. Wu, Y. Hu, H. Zhuo, Z. Chen et al., A mechanically strong and sensitive CNT/rGO–CNF carbon aerogel for piezoresistive sensors. J. Mater. Chem. A 6, 23550–23559 (2018). https://doi.org/10.1039/C8TA09322A
Article CAS Google Scholar
Q. Zheng, J.-H. Lee, X. Shen, X. Chen, J.-K. Kim, Graphene-based wearable piezoresistive physical sensors. Mater. Today 36, 158–179 (2020). https://doi.org/10.1016/j.mattod.2019.12.004
Article CAS Google Scholar
X. He, Q. Liu, W. Zhong, J. Chen, D. Sun et al., Strategy of constructing light-weight and highly compressible graphene-based aerogels with an ordered unique configuration for wearable piezoresistive sensors. ACS Appl. Mater. Interfaces 11, 19350–19362 (2019). https://doi.org/10.1021/acsami.9b02591
Article CAS PubMed Google Scholar
X. Chen, D. Lai, B. Yuan, M.-L. Fu, Fabrication of superelastic and highly conductive graphene aerogels by precisely “unlocking” the oxygenated groups on graphene oxide sheets. Carbon 162, 552–561 (2020). https://doi.org/10.1016/j.carbon.2020.02.082
Article CAS Google Scholar
Q. Wu, Y. Qiao, R. Guo, S. Naveed, T. Hirtz et al., Triode-mimicking graphene pressure sensor with positive resistance variation for physiology and motion monitoring. ACS Nano 14, 10104–10114 (2020). https://doi.org/10.1021/acsnano.0c03294
Article CAS PubMed Google Scholar
C. Long, X. **e, J. Fu, Q. Wang, H. Guo et al., Supercapacitive brophene-graphene aerogel as elastic-electrochemical dielectric layer for sensitive pressure sensors. J. Colloid Interface Sci. 601, 355–364 (2021). https://doi.org/10.1016/j.jcis.2021.05.116
Article CAS PubMed ADS Google Scholar
H. Tian, Y. Shu, X.F. Wang, M.A. Mohammad, Z. Bie et al., A graphene-based resistive pressure sensor with record-high sensitivity in a wide pressure range. Sci. Rep. 5, 8603 (2015). https://doi.org/10.1038/srep08603
Article CAS PubMed PubMed Central Google Scholar
J. **ao, Y. Tan, Y. Song, Q. Zheng, A flyweight and superelastic graphene aerogel as a high-capacity adsorbent and highly sensitive pressure sensor. J. Mater. Chem. A 6, 9074–9080 (2018). https://doi.org/10.1039/C7TA11348J
Article CAS Google Scholar
T. Zhai, L. Verdolotti, S. Kacilius, P. Cerruti, G. Gentile et al., High piezo-resistive performances of anisotropic composites realized by embedding rGO-based chitosan aerogels into open cell polyurethane foams. Nanoscale 11, 8835–8844 (2019). https://doi.org/10.1039/c9nr00157c
Article CAS PubMed Google Scholar
T. Zhai, J. Li, X. Wang, W. Yan, C. Zhang et al., Carbon-based aerogel in three-dimensional polyurethane scaffold: the effect of in situ unidirectional aerogel growth on piezoresistive properties. Sens. Actuat. A Phys. 333, 113306 (2022). https://doi.org/10.1016/j.sna.2021.113306
Article CAS Google Scholar
H. Zhuo, Y. Hu, X. Tong, Z. Chen, L. Zhong et al., A supercompressible, elastic, and bendable carbon aerogel with ultrasensitive detection limits for compression strain, pressure, and bending angle. Adv. Mater. 30, e1706705 (2018). https://doi.org/10.1002/adma.201706705
Article CAS PubMed Google Scholar
S. Wu, S. Tian, R. Jian, L. Zhou, T. Luo et al., Bio-inspired salt-fouling resistant graphene evaporators for solar desalination of hypersaline brines. Desalination 546, 116197 (2023). https://doi.org/10.1016/j.desal.2022.116197
Article CAS Google Scholar
H. Zhang, H. Liu, S. Chen, X. Zhao, F. Yang et al., Preparation of three-dimensional graphene-based sponge as photo-thermal conversion material to desalinate seawater. Chem. Res. Chin. Univ. 38, 1425–1434 (2022). https://doi.org/10.1007/s40242-022-1500-8
Article CAS Google Scholar
X. Meng, J. Yang, S. Ramakrishna, Y. Sun, Y. Dai, Gradient-aligned Au/graphene meshes with confined heat at multiple levels for solar evaporation and anti-gravity catalytic conversion. J. Mater. Chem. A 8, 16570–16581 (2020). https://doi.org/10.1039/D0TA04986G
Article CAS Google Scholar
Y. Hu, H. Yao, Q. Liao, T. Lin, H. Cheng et al., The promising solar-powered water purification based on graphene functional architectures. EcoMat 4, e12205 (2022). https://doi.org/10.1002/eom2.12205
Article CAS Google Scholar
L. Chen, J. Wei, Q. Tian, Z. Han, L. Li et al., Dual-functional graphene oxide-based photothermal materials with aligned channels and oleophobicity for efficient solar steam generation. Langmuir 37, 10191–10199 (2021). https://doi.org/10.1021/acs.langmuir.1c01647
Article CAS PubMed Google Scholar
Z. Luo, X. Wang, D. Yang, S. Zhang, T. Zhao et al., Photothermal hierarchical carbon nanotube/reduced graphene oxide microspherical aerogels with radially orientated microchannels for efficient cleanup of crude oil spills. J. Colloid Interface Sci. 570, 61–71 (2020). https://doi.org/10.1016/j.jcis.2020.02.097
Article CAS PubMed ADS Google Scholar
X. Ming, A. Guo, Q. Zhang, Z. Guo, F. Yu et al., 3D macroscopic graphene oxide/MXene architectures for multifunctional water purification. Carbon 167, 285–295 (2020). https://doi.org/10.1016/j.carbon.2020.06.023
Article CAS Google Scholar
M. **, Z. Wu, F. Guan, D. Zhang, B. Wang et al., Hierarchically designed three-dimensional composite structure on a cellulose-based solar steam generator. ACS Appl. Mater. Interfaces 14, 12284–12294 (2022). https://doi.org/10.1021/acsami.1c24847
Article CAS PubMed Google Scholar
X. Zhao, X.-J. Zha, L.-S. Tang, J.-H. Pu, K. Ke et al., Self-assembled core-shell polydopamine@MXene with synergistic solar absorption capability for highly efficient solar-to-vapor generation. Nano Res. 13, 255–264 (2020). https://doi.org/10.1007/s12274-019-2608-0
Article CAS Google Scholar
Z. Lei, X. Sun, S. Zhu, K. Dong, X. Liu et al., Nature inspired MXene-decorated 3D honeycomb-fabric architectures toward efficient water desalination and salt harvesting. Nano-Micro Lett. 14, 10 (2021). https://doi.org/10.1007/s40820-021-00748-7
Article CAS ADS Google Scholar
F. Wu, S. Qiang, X.-D. Zhu, W. Jiao, L. Liu et al., Fibrous MXene aerogels with tunable pore structures for high-efficiency desalination of contaminated seawater. Nano-Micro Lett. 15, 71 (2023). https://doi.org/10.1007/s40820-023-01030-8
Article CAS ADS Google Scholar
Q. Zhang, G. Yi, Z. Fu, H. Yu, S. Chen et al., Vertically aligned Janus MXene-based aerogels for solar desalination with high efficiency and salt resistance. ACS Nano 13, 13196–13207 (2019). https://doi.org/10.1021/acsnano.9b06180
Article CAS PubMed Google Scholar
H. Gao, N. Bing, Z. Bao, H. **e, W. Yu, Sandwich-structured MXene/wood aerogel with waste heat utilization for continuous desalination. Chem. Eng. J. 454, 140362 (2023). https://doi.org/10.1016/j.cej.2022.140362
Article CAS Google Scholar
Z. Zheng, H. Liu, D. Wu, X. Wang, Polyimide/MXene hybrid aerogel-based phase-change composites for solar-driven seawater desalination. Chem. Eng. J. 440, 135862 (2022). https://doi.org/10.1016/j.cej.2022.135862
Article CAS Google Scholar
H. Zhang, X. Shen, E. Kim, M. Wang, J.-H. Lee et al., Integrated water and thermal managements in bioinspired hierarchical MXene aerogels for highly efficient solar-powered water evaporation. Adv. Funct. Mater. 32, 2111794 (2022). https://doi.org/10.1002/adfm.202111794
Article CAS Google Scholar
W. Li, X. Li, W. Chang, J. Wu, P. Liu et al., Vertically aligned reduced graphene oxide/Ti3C2Tx MXene hybrid hydrogel for highly efficient solar steam generation. Nano Res. 13, 3048–3056 (2020). https://doi.org/10.1007/s12274-020-2970-y
Article CAS ADS Google Scholar
C. Wu, S. Zhou, C. Wang, J. Zhang, Z. Yang et al., Aerogels based on MXene nanosheet/reduced graphene oxide composites with vertically aligned channel structures for solar-driven vapor generation. ACS Appl. Nano Mater. 6, 4455–4464 (2023). https://doi.org/10.1021/acsanm.2c05548
Article CAS Google Scholar
X. Hu, J. Zhu, Tailoring aerogels and related 3D macroporous monoliths for interfacial solar vapor generation. Adv. Funct. Mater. 30, 1907234 (2020). https://doi.org/10.1002/adfm.201907234
Article CAS Google Scholar
Z. Yin, H. Wang, M. Jian, Y. Li, K. **a et al., Extremely black vertically aligned carbon nanotube arrays for solar steam generation. ACS Appl. Mater. Interfaces 9, 28596–28603 (2017). https://doi.org/10.1021/acsami.7b08619
Article CAS PubMed Google Scholar
H.-J. Zhan, J.-F. Chen, H.-Y. Zhao, L. Jiao, J.-W. Liu et al., Biomimetic difunctional carbon-nanotube-based aerogels for efficient steam generation. ACS Appl. Nano Mater. 3, 4690–4698 (2020). https://doi.org/10.1021/acsanm.0c00683
Article CAS Google Scholar
P. Mu, Z. Zhang, W. Bai, J. He, H. Sun et al., Superwetting monolithic hollow-carbon-nanotubes aerogels with hierarchically nanoporous structure for efficient solar steam generation. Adv. Energy Mater. 9, 1802158 (2019). https://doi.org/10.1002/aenm.201802158
Article CAS Google Scholar
B. Zhu, H. Kou, Z. Liu, Z. Wang, D.K. Macharia et al., Flexible and washable CNT-embedded PAN nonwoven fabrics for solar-enabled evaporation and desalination of seawater. ACS Appl. Mater. Interfaces 11, 35005–35014 (2019). https://doi.org/10.1021/acsami.9b12806
Article CAS PubMed Google Scholar
S. Xu, J. Zhang, Vertically aligned graphene for thermal interface materials. Small Struct. 1, 2000034 (2020). https://doi.org/10.1002/sstr.202000034
Article Google Scholar
F. An, X. Li, P. Min, H. Li, Z. Dai et al., Highly anisotropic graphene/boron nitride hybrid aerogels with long-range ordered architecture and moderate density for highly thermally conductive composites. Carbon 126, 119–127 (2018). https://doi.org/10.1016/j.carbon.2017.10.011
Article CAS Google Scholar
G. Yang, Y. Yang, T. Chen, J. Wang, L. Ma et al., Graphene/MXene composite aerogels reinforced by polyimide for pressure sensing. ACS Appl. Nano Mater. 5, 1068–1077 (2022). https://doi.org/10.1021/acsanm.1c03722
Article CAS Google Scholar
B. Wicklein, A. Kocjan, G. Salazar-Alvarez, F. Carosio, G. Camino et al., Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide. Nat. Nanotechnol. 10, 277–283 (2015). https://doi.org/10.1038/nnano.2014.248
Article CAS PubMed ADS Google Scholar
Y. Zhang, Y. Li, Q. Lei, X. Fang, H. **e et al., Tightly-packed fluorinated graphene aerogel/polydimethylsiloxane composite with excellent thermal management properties. Compos. Sci. Technol. 220, 109302 (2022). https://doi.org/10.1016/j.compscitech.2022.109302
Article CAS Google Scholar
Y.R. Jeong, H. Park, S.W. **, S.Y. Hong, S.-S. Lee et al., Highly stretchable and sensitive strain sensors using fragmentized graphene foam. Adv. Funct. Mater. 25, 4228–4236 (2015). https://doi.org/10.1002/adfm.201501000
Article CAS Google Scholar
C. Hu, J. Xue, L. Dong, Y. Jiang, X. Wang et al., Scalable preparation of multifunctional fire-retardant ultralight graphene foams. ACS Nano 10, 1325–1332 (2016). https://doi.org/10.1021/acsnano.5b06710
Article CAS PubMed Google Scholar
T. Xue, W. Fan, X. Zhang, X. Zhao, F. Yang et al., Layered double hydroxide/graphene oxide synergistically enhanced polyimide aerogels for thermal insulation and fire-retardancy. Compos. Part B Eng. 219, 108963 (2021). https://doi.org/10.1016/j.compositesb.2021.108963
Article CAS Google Scholar
M. Šilhavík, P. Kumar, Z.A. Zafar, R. Král, P. Zemenová et al., High-temperature fire resistance and self-extinguishing behavior of cellular graphene. ACS Nano 16, 19403–19411 (2022). https://doi.org/10.1021/acsnano.2c09076
Article CAS PubMed Google Scholar
B.-X. Li, Z. Luo, W.-G. Yang, H. Sun, Y. Ding et al., Adaptive and adjustable MXene/reduced graphene oxide hybrid aerogel composites integrated with phase-change material and thermochromic coating for synchronous visible/infrared camouflages. ACS Nano 17, 6875–6885 (2023). https://doi.org/10.1021/acsnano.3c00573
Article CAS PubMed Google Scholar
S. Hou, X. Wu, Y. Lv, W. Jia, J. Guo et al., Ultralight, highly elastic and bioinspired capillary-driven graphene aerogels for highly efficient organic pollutants absorption. Appl. Surf. Sci. 509, 144818 (2020). https://doi.org/10.1016/j.apsusc.2019.144818
Article CAS Google Scholar
J. Wu, B. Liang, J. Huang, S. Xu, Z. Yan, Honeycomb-like rGO aerogels via oriented freeze-drying as efficient organic solvents removing absorbents. Mater. Lett. 318, 132164 (2022). https://doi.org/10.1016/j.matlet.2022.132164
Article CAS Google Scholar
W. Wan, F. Zhang, S. Yu, R. Zhang, Y. Zhou, Hydrothermal formation of graphene aerogel for oil sorption: the role of reducing agent, reaction time and temperature. New J. Chem. 40, 3040–3046 (2016). https://doi.org/10.1039/C5NJ03086B
Article CAS Google Scholar
H. Liu, Y. Xu, D. Han, J.-P. Cao, F. Zhao et al., Leaf-structured carbon nanotubes/graphene aerogel and the composites with polydimethylsiloxane for electromagnetic interference shielding. Mater. Lett. 313, 131751 (2022). https://doi.org/10.1016/j.matlet.2022.131751
Article CAS Google Scholar
Y. Chen, H. Zhang, G. Zeng, Tunable and high performance electromagnetic absorber based on ultralight 3D graphene foams with aligned structure. Carbon 140, 494–503 (2018). https://doi.org/10.1016/j.carbon.2018.09.014
Article CAS Google Scholar
Z. Zeng, C. Wang, Y. Zhang, P. Wang, S.I. Seyed Shahabadi et al., Ultralight and highly elastic graphene/lignin-derived carbon nanocomposite aerogels with ultrahigh electromagnetic interference shielding performance. ACS Appl. Mater. Interfaces 10, 8205–8213 (2018). https://doi.org/10.1021/acsami.7b19427
Article CAS PubMed Google Scholar
Z. Zeng, Y. Zhang, X.Y.D. Ma, S.I.S. Shahabadi, B. Che et al., Biomass-based honeycomb-like architectures for preparation of robust carbon foams with high electromagnetic interference shielding performance. Carbon 140, 227–236 (2018). https://doi.org/10.1016/j.carbon.2018.08.061
Article CAS Google Scholar
Q. Zhang, Z. Du, M. Hou, Z. Ding, X. Huang et al., Ultralight, anisotropic, and self-supported graphene/MWCNT aerogel with high-performance microwave absorption. Carbon 188, 442–452 (2022). https://doi.org/10.1016/j.carbon.2021.11.047
Article CAS Google Scholar
S. Zhao, H.-B. Zhang, J.-Q. Luo, Q.-W. Wang, B. Xu et al., Highly electrically conductive three-dimensional Ti₃C₂T_x MXene/reduced graphene oxide hybrid aerogels with excellent electromagnetic interference shielding performances. ACS Nano 12, 11193–11202 (2018). https://doi.org/10.1021/acsnano.8b05739
Article CAS PubMed Google Scholar
L. Liang, Q. Li, X. Yan, Y. Feng, Y. Wang et al., Multifunctional magnetic Ti₃C₂T_x MXene/graphene aerogel with superior electromagnetic wave absorption performance. ACS Nano 15, 6622–6632 (2021). https://doi.org/10.1021/acsnano.0c09982
Article CAS PubMed Google Scholar

Download references

Acknowledgements

The financial support by the National Natural Science Foundation of China (No. 52002020) is acknowledged.

Author information

Authors and Affiliations

Bei**g Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Bei**g, Bei**g, 100083, People’s Republic of China
Ying Wu, Chao An, Yaru Guo, Yangyang Zong & Naisheng Jiang
Institute of Materials Intelligent Technology, Liaoning Academy of Materials, Shenyang, 110004, People’s Republic of China
Ying Wu, Chao An, Yaru Guo, Yangyang Zong & Naisheng Jiang
School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Shenzhen, Guangdong, 518172, People’s Republic of China
Qingbin Zheng
State Key Laboratory of Organic-Inorganic Composites, College of Materials Science and Engineering, Bei**g University of Chemical Technology, Bei**g, 100029, People’s Republic of China
Zhong-Zhen Yu

Authors

Ying Wu
View author publications
You can also search for this author in PubMed Google Scholar
Chao An
View author publications
You can also search for this author in PubMed Google Scholar
Yaru Guo
View author publications
You can also search for this author in PubMed Google Scholar
Yangyang Zong
View author publications
You can also search for this author in PubMed Google Scholar
Naisheng Jiang
View author publications
You can also search for this author in PubMed Google Scholar
Qingbin Zheng
View author publications
You can also search for this author in PubMed Google Scholar
Zhong-Zhen Yu
View author publications
You can also search for this author in PubMed Google Scholar

Corresponding authors

Correspondence to Ying Wu, Qingbin Zheng or Zhong-Zhen Yu.

Ethics declarations

Conflict of interest

The authors declare no interest confict. They have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and permissions

About this article

Cite this article

Wu, Y., An, C., Guo, Y. et al. Highly Aligned Graphene Aerogels for Multifunctional Composites. Nano-Micro Lett. 16, 118 (2024). https://doi.org/10.1007/s40820-024-01357-w

Download citation

Received: 07 November 2023
Accepted: 03 January 2024
Published: 15 February 2024
DOI: https://doi.org/10.1007/s40820-024-01357-w

Keywords

Use our pre-submission checklist

Avoid common mistakes on your manuscript.

Highly Aligned Graphene Aerogels for Multifunctional Composites

Highlights

Abstract

Similar content being viewed by others

Aligned-graphene composites: a review

Graphene Nanoarchitectonics: Approaching the Excellent Properties of Graphene from Microscale to Macroscale

Aerogels based on carbon nanomaterials

1 Introduction

2.1.2 Bidirectional Freeze Casting

2.1.3 Radial Freeze Casting

2.2 Self-Assembly Induced Alignment

2.3 Shear-Induced Alignment

2.4 Further Enhancement of Alignment

2.5 Comparison of the Aligning Techniques

2.6 Fabrication of Highly Aligned Graphene Aerogel/Polymer Composites

3 Fundamental Properties

3.1 Anisotropic Properties

3.2 Contributions of Alignment to Physical Properties of Composites

3.2.1 Electrical Conductivity

3.2.2 Fracture Toughness

3.2.3 Thermal Conductivity

4 Quantitative Characterization Techniques of the Graphene Alignment

4.1 SEM Image-Based Orientation Distribution Analysis

4.2 Polarized Raman Spectroscopy

4.3 X-ray Scattering

4.4 Comparison of the Characterization Techniques

5 Multifunctional Applications

5.1 Energy Conersion and Storage

5.1.1 Solar-Thermal Energy Conversion

5.1.3 Supercapacitor and Electrochemical Thermocell

5.2 Super-Elasticity and Piezoresistive Sensors

5.3 Solar Steam

5.4 Thermal Management

5.5 Organic Absorption

5.6 EMI Shielding

6 Conclusions and Perspectives

Abbreviations

References

Acknowledgements

Author information

Authors and Affiliations

Corresponding authors

Ethics declarations

Conflict of interest

Rights and permissions

About this article

Cite this article

Share this article

Keywords

Search

Navigation