Introduction

The development of effective and sustainable technologies to transform CO2 into value-added products has received considerable attention due to the increased global warming by high CO2 emissions1,2,55. These materials are ranked based on various metrics that are crucial for practical applications, encompassing adsorption capacity, adsorption rate, thermal stability, adsorption selectivity, and cycle stability. Remarkably, quaternized CNF emerges as the good performer among its counterparts. The ability to achieve strong adsorption is important to enable contact-electro-catalytic CO2RR.

Fig. 3: Mechanism of contact-electro-catalytic CO2RR.
figure 3

a Comparison of CO2-temperature programmed desorption (TPD) between quaternized CNF and Cu-PCN@PVDF. The inset is an amplification of the TCD signal in the range of 55 °C−125 °C. b Comparison of CO2 vapor adsorption at room temperature and pressure of quaternized CNF and Cu-PCN@PVDF with high and low CO2 concentrations. c A performance comparison of quaternized CNF with other materials that adsorb CO2. d Comparison of product yields of quaternized CNF-based TENG and pure CNF-based TENG under different CO2 concentrations for contact-electro-catalytic CO2RR. e, f Comparison of the current change of contact-electro-catalytic CO2RR of quaternary ammoniated CNF-based TENG and pure CNF-based TENG under high and low CO2 concentrations. g–i Comparison of adsorption energies of quaternized CNF for CO2, O2 and N2 molecules. j Analysis of the total density of states (TDOS) of Cu-PCN, projected density of states (PDOS) on Cu and the TDOS on PCN. k, l The electron distribution of the conduction band edge of PCN and Cu-PCN (iso surface = 0.004). m Charge distribution near Cu-PCN surface during contact. Source data are provided as a Source Data file.

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Subsequent experimentation delved into the impact of varying CO2 concentrations on the yield of contact-electro-catalytic CO2RR, as illustrated in Fig. 3d. The results indicate that, as the CO2 concentration decreases from 20% to 0.02%, the yield of CO product in the contact-electro-catalytic CO2RR catalyzed by both quaternized CNF-based and pure CNF-based TENGs diminishes. The quaternized CNF-based TENG outperforms its pure CNF-based counterpart across both high and low concentration ranges. This phenomenon can be elucidated through two distinct avenues. Primarily, the TENG’s current output escalates as the CO2 concentration rises after reacting for 5 h, ultimately culminating in an augmented charge transfer for contact-electro-catalysis, which facilitates an upsurge in the production of CO. Secondly, in contrast to lower CO2 concentrations, the surface of quaternized ammoniated CNF exhibits heightened CO2 adsorption at elevated concentrations. This translates to an increased involvement of reaction substrates in the contact-electro-catalytic process, consequently leading to an augmentation in CO production. A noteworthy achievement emerges from this study-successful contact-electro-catalytic CO2RR under experimental conditions featuring even lower CO2 concentrations (i.e., 0.02%) than those present in ambient air (~0.04%). This result indicates a way for further explorations into the catalytic prowess of TENG in real-world atmospheric conditions.

The output current of TENG in the contact-electro-catalytic CO2RR process will exhibit distinctive fluctuations under the influence of the two tribolayers on CO2 adsorption. As shown in Fig. 3e, the output current shows an initial fall followed by a climb when there are high CO2 levels present (20%). Under this condition, CO2 is first adsorbed by the electropositive quaternary ammoniated CNF, leading to a decrease in current. This is owing to the electron-withdrawing effect of the carbonic acid double bond, which will withdraw electrons during the contact electrification process, resulting in a drop in the hole density of the electropositive quaternized CNF56,57. As the reaction proceeds, surplus CO2 gradually finds residence within the interstices of PVDF electrospun fibers. This gradual accommodation imparts heightened electronegativity to the Cu-PCN@PVDF tribolayer, thereby engendering a commensurate augmentation in electrical output. However, when we eliminated the effect of the quaternary amino functional groups in the quaternized CNFs, the current showed a single changing trend, as shown in Fig. 3f. After the electropositive tribolayer quaternized CNF was replaced by pure CNF, CO2 was only adsorbed on the Cu-PCN@PVDF tribolayer, which led to an increase in the electron density on the electronegative tribolayer and a consequent increase in the electrical output. Nevertheless, with a reduction in CO2 concentration to 0.02%, a distinct shift in the output current pattern emerged. Precisely, when employing the electropositive quaternized ammoniated CNF as the tribolayer in TENG, predominant adsorption takes place upon the quaternary ammoniated functional groups, leading to an ensuing continuous decrement in current. Similarly, upon substitution of quaternized CNF with pure CNF, the locus of CO2 adsorption transitioned to Cu-PCN@PVDF, consequentially fostering an elevation in the output current. Given that the adsorbed quantity of CO2 at diminished concentrations markedly contrasts with that at higher concentrations, a corollary emerges for pure CNF-based TENG. In this context, the surge in current at heightened concentrations surpasses the increment observed at lower concentrations.

Based on the study of CO2 adsorption performance, we further proposed the mechanism of contact-electro-catalytic CO2RR. During the contact electrification process of TENG, quaternized CNF effectively adsorb CO2 molecules from the surrounding environment. Simultaneously, within the Cu-PCN@PVDF material, single-atom copper plays a crucial role in accumulating electrons and assisting electron transfer. When these two tribolayers come into contact, the electrons, accumulated by the presence of single-atom copper, which facilitate the electron transfer to the adsorbed CO2 molecules, thereby driving and completing a catalytic reaction. To deeply study the CO2 adsorption, DFT calculations were carried out to calculate the binding energy of CO2 to quaternized CNF, and the results show that the adsorption energy between quaternized CNF and CO2 molecules is 0.7 eV. Moreover, to investigate the potential competitive adsorption between CO2, O2, and N2 on the quaternized CNF surface, the adsorption energies of CO2 (-0.7 eV), O2 (-0.41 eV) and N2 (-0.08 eV) molecules were further calculated, as illustrated in Fig. 3g-i. The highest adsorption energy of CO2 indicates it has the strongest adsorption on the electrode surface. Moreover, it is worth noting that the contact-electro-catalytic CO2RR was carried out at an environmental humidity of 99% to ensure an ample supply of protons, which were essential for the reduction reaction. During the catalytic reaction, CO2 can interact strongly with the H2O, as suggested by the discernible acidity of the water droplet collected after the reaction (as depicted in Supplementary Fig. 18 and Supplementary Note 12). This interaction between H2O and CO2 has the possibility to further enhance the interaction between CO2 and quaternized CNF. Furthermore, DFT calculations were conducted to investigate the role of electron enrichment from Cu-PCN. The analysis of the density of states (DOS) shows that pure PCN exhibits typical semiconductor characteristics, as well established by other study58,59. Upon the introduction of the Cu atoms into the PCN structure, a strong hybridized peak emerges between Cu and the PCN substrate, indicating the strong interaction that stabilizes Cu on the PCN substrate. Of greater significance, the incorporation of Cu leads to the formation of a defect state near the conduction band edge (indicated by the arrow in Fig. 3j), resulting in a reduction of the band gap that will facilitate the electron injection. This defect state primarily arises from the presence of Cu, suggesting that upon injection into Cu-PCN, electrons will accumulate around the Cu atoms. Furthermore, electron distributions of PCN and Cu-PCN were computed, as depicted in Fig. 3k and l. The findings reveal that electrons in PCN are comparatively scattered, whereas electrons in Cu-PCN predominantly concentrate on copper atoms. This substantiates the electron enrichment effect attributed to the presence of single-atom copper in the Cu-PCN catalyst.

Finally, to validate the electron transfer mechanism, we conducted DFT calculations, providing insights into the charge distribution near the Cu-PCN surface during the contact process, as shown in Fig. 4m. When the separation distance between CO2 molecules and Cu atoms exceeds 4 Å, no significant interaction is observed between the charges of CO2 and Cu atoms on the Cu-PCN surface. However, when the distance is reduced to <4 Å, electron accumulation occurs between the O atom of CO2 and the Cu atom. This accumulation intensifies as the CO2 molecule further approaches the Cu atom, leading to a noticeable build-up of electrons. Consequently, upon contact between CO2 and Cu, electrons could swiftly transfer from the Cu atom to the CO2 molecule. When there is no Cu atom on the PCN surface, a similar electron accumulation occurs as CO2 molecules approach the PCN surface (Supplementary Fig. 19). However, the electron density between them is notably lower compared to the Cu-PCN interaction. As a result, when CO2 and PCN come into contact, the efficiency of electron transfer is significantly reduced, underscoring the crucial role of single-atom copper in the electron transfer process.

Fig. 4: Contact-electro-catalytic CO2RR from ambient air.
figure 4

a Photograph of the device for contact-electro-catalytic CO2RR in a closed box at 99% RH. b CO2 breakthrough curves of quaternized CNF under dry and wet (99% RH) ambient air feed at 25 °C. c Comparison of CO2 adsorption capacity of quaternized CNF and Cu-PCN@PVDF in dry and wet air. d, e GC chromatography and real-time current change of contact-electro-catalytic CO2RR in air. f Calculation of transferred charges during contact-electro-catalytic CO2RR in air. The inset is a magnification of the start and end of the integrated charge. g Schematic illustration of contact-electro-catalytic CO2 reduction in air. Source data are provided as a Source Data file.

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Contact-electro-catalytic CO2RR from ambient air

As the driving force behind TENG’s generation of contact-electro-catalytic charges predominantly originates from ambient mechanical energy, the contact electrically induced interfacial CO2RR holds promise for eventual application in atmospheric settings, effecting the reduction of excess CO2 in our environment. Moreover, the good CO2 adsorption performance of quaternized CNF lays a strong foundation for CNF-based TENG application in catalyzing the reduction reaction of CO2 in air. To realize contact-electro-catalytic CO2RR in air under experimental conditions, we used compressed air as the gas source instead of the CO2/Ar mixed gas. The experiment was conducted in a confined box under normal temperature and pressure conditions with 99% humidity maintained by distilled water, as shown in Fig. 4a. First, a fixed-bed CO2 breakthrough experiment was conducted on the quaternized CNF utilizing ambient air feed, which contained ~400 ppm of CO2. This experiment was aimed to assess the CO2 adsorption capabilities of the material within ambient air environment, as illustrated in Fig. 4b. The tests were carried out under flowing air conditions to simulate real-world conditions more realistically. The calculated fixed bed breakthrough capacities were 6.25 ml g-1 and 5.3 ml g-1 under dry and wet conditions, respectively (Fig. 4c). The observed breakthrough curves were steep and sharp indicating fast mass transfer in the fixed-bed. The high CO2 adsorption capacities of quaternized CNF at low CO2 concentrations under both dry and humid conditions indicate that quaternized CNF is a good candidate for capturing carbon dioxide from dilute gas streams (i.e., ambient air).

Based on the good CO2 adsorption performance of quaternized CNF in air, quaternized CNF-Cu-PCN@PVDF-based TENG can catalyze the reduction reaction of CO2 in air. After the reaction for 10.5 h, 235.65 nmol of CO is produced in the airtight box, and its GC spectrum is shown in Fig. 4d. Furthermore, real-time current changes during the reaction were recorded, as shown in Fig. 4e. The entire catalytic reaction process lasted for 10.5 h, and the current showed a trend of increasing first and then decreasing. However, when the compressed air in the system is replaced with Ar, an interesting phenomenon is observed: initially, the current tends to increase before reaching a stable level, and notably, the current does not exhibit a subsequent decrease, as shown in Supplementary Fig. 20. This observation indicates that the contact-electro-catalytic reaction takes place within the air environment, while such a reaction does not manifest when Ar is used instead. Furthermore, we calculated the transferred charges with the CO2RR reaction, as shown in Fig. 4f. Similar to the method for calculating the transferred charge, the transferred charge with CO2RR was obtained by current integration. The calculated transfer charge of contact-electro-catalytic CO2RR in air is 48.4 mC. Subsequently, we compared the CO yield of contact-electro-catalytic CO2RR in air compared with the conventional photocatalysis, as shown in Supplementary Fig. 21 and Table 5. The CO yield of contact-electro-catalytic CO2RR is 33 μmol g-1 h-1, which is a good indicator for the yield of CO produced by catalytic CO2RR in air60,61,62,63,64. Schematic illustration of contact-electro-catalytic CO2RR in air is shown in Fig. 4g. In the fictional scenario, atmospheric CO2 is drawn into the wind-driven TENG device. During the interaction of the TENG’s quaternized CNF tribolayer with the Cu-PCN@PVDF components, mechanical energy is converted into electrical energy. This process catalyzes the reduction of atmospheric CO2 to CO through the CO2RR. Subsequently, the performance of the wind-driven TENG device and the impact of wind energy on CO generation during the CO2RR process were comprehensively evaluated, as shown in Supplementary Fig. 22 and Supplementary Note 13. The results show that the FECO of the wind-driven TENG device is ~92%, which is comparable to the FECO (93.95%) obtained for the motor-driven TENG device. The slight variation in FECO can be attributed to the influence of the gas flow on the CO2 adsorption and product desorption process. The utilization of quaternized CNF in conjunction with the unique properties of the quaternized CNF-Cu-PCN@PVDF based TENG opens up avenues for efficient and sustainable CO2 reduction within air environments, holding promise for advancing carbon capture and utilization technologies.

Discussion

We report a stride in contact-electro-catalytic CO2 reduction, offering a promising solution to the pressing challenge of sustainable carbon dioxide mitigation. Achieving a CO Faradaic efficiency exceeding 96%, it highlights an impressive conversion of CO2. Noteworthy is a good CO yield of 33 μmol g-1 h-1, attained even in ambient air, setting a benchmark for catalytic CO2RR under low CO2 conditions. The mechanism relies on the good CO2 adsorption capacity of quaternized CNF, synergistically coupled with the electron-enrichment attributes of single-atom copper within Cu-PCN, which drives the contact-electro-catalytic CO2RR process. This study not only advances CO2 reduction technologies but also sets the path for the development of methodologies for wider contact-electro-catalytic applications.

The concept of single-atom catalysis in the CO2RR field represents a cutting-edge pathway in catalysis. The seamless integration of porous coordination network technology and electrospinning enables the incorporation of different emerging single-atom catalysts into the contact-electro-catalytic system. This is poised to emerge as a universal strategy for achieving efficient catalytic platform that can power carbon dioxide reduction as well as other sustainable chemical manufacturing using industrial waste feedstock. Moreover, compared to traditional catalytic methods that typically demand substantial energy inputs, TENGs employs mechanical energy harvested from the environment to power CO2RR. This not only circumvents the inherent energy consumption challenges of traditional methods but also harnesses a sustainable and environmentally friendly energy source.

Going forward, future research could focus on translating this unique contact-electro-catalytic platform into translational impact, such as incorporating it into wearables or employing it in localized carbon capture and utilization settings. These advancements could significantly contribute to mitigating CO2 emissions and combating climate change. Moreover, in future investigations, through the optimization of catalyst type and the number of catalytic sites, contact-electro-catalytic CO2RR holds the potential to generate products of higher value than CO, particularly in the realm of liquid products.

Methods

Chemical reagents

Mechanically refined cellulose nanofibril (CNF, 3.4% w/w aqueous suspension) was purchased from Tian** Wood Elf Biotechnology Co., Ltd. Urea (CO(NH2)2, 99%), copper chloride (CuCl2·2H2O, 99.0%), polyvinylidene fluoride (PVDF, average Mw~534000), lycidyltrimethylammonium chloride (GTMAC, ≥90%), acetone (≥99.5%), N, N-Dimethylformamide (DMF, ≥99.9%), dimethyl sulfoxide (DMSO, ≥99.9%) and tetrabutylammonium hydroxide 30-hydrate (TBAH, ≥98.0%) were purchased from Sigma-Aldrich and used without further modification. DI water (18.2 MΩ) was used in all the experiments.

Preparation of electrospun Cu-PCN@PVDF film

The preparation of Cu-PCN single-atom catalyst is shown in Supplementary Fig. 4. 0.7 g of PVDF powder was mixed with 2.9 g of acetone and stirred at room temperature. Different amounts of Cu-PCN powder (3.5 mg, 7 mg and 10.5 mg) were mixed with 1.9 g DMF and sonicated for 10 min. The Cu-PCN/DMF mixture was slowly added into PVDF/acetone, and the stirring was continued for 24 h. Furthermore, the quantity of single-atom copper in Cu-PCN can be conveniently tailored by utilizing CuCl2 precursor solutions with varying concentrations. The specific preparation method is detailed in Supplementary Fig. 4. The mixture (about 4 mL) was electrospun. The parameters were: 15 KV voltage, 1 mL/h speed, 4 h,10 cm distance, and the receiving plate area is 165 cm2.

Preparation of quaternized CNF-Cu-PCN@PVDF based TENG

The preparation of quaternized CNF film is shown in Supplementary Fig. 1a. The quaternized CNF film (100 μm thickness) was cut into a size of “4 cm × 4 cm”, and the aluminum electrode was pasted on the back, and copper wires were drawn out; the static-spun Cu-PCN@PVDF membrane (297 μm thickness) was cut into a size of “4 cm × 4 cm”, and copper wires were drawn from the tin foil electrodes on the back. The backs of the two electrodes were affixed with double-sided tape to form a quaternary ammoniated CNF-Cu-PCN@PVDF based TENG.

System design of contact-electro-catalytic CO2RR

Contact-electro-catalytic CO2RR was conducted within a sealed chamber fitted with a motor. Distilled water was placed inside the sealed box to maintain the ambient humidity at 99%. Prior to testing, argon gas was introduced into the sealed chamber to purge the air. Once the current from the TENG stabilizes, CO2 was introduced through the air inlet, and the reaction proceeded for 5 h. At hourly intervals, a syringe was used to extract 1 mL of gas from the sealed chamber for Gas Chromatography analysis.

Calculation of the Faradaic efficiency

The product Faradaic efficiency (FE) was calculated using the following equation:

$${{{{{\rm{FE}}}}}}=\frac{{{{{{\rm{Z}}}}}}\times {{{{{\rm{n}}}}}}\times {{{{{\rm{F}}}}}}}{{{{{{\rm{Q}}}}}}}\times 100\%$$

Where \({{{{{\rm{Z}}}}}}\) is the number of electrons transferred, \({{{{{\rm{n}}}}}}\) is the amount of product (mol), \({{{{{\rm{F}}}}}}\) is the Faraday constant (F = 96485 C/mol); \({{{{{\rm{Q}}}}}}\) is the transferred charge (C).

Calculation of the CO yield

In the fabrication process of the quaternized CNF-Cu-PCN@PVDF based TENG, a precise amount of 7 mg of Cu-PCN was blended with 0.7 g of PVDF to facilitate the subsequent electrospinning procedure. The dimensions of the aluminum foil membrane, which acted as the substrate for electrospinning, were measured at “11 cm × 15 cm”. Subsequently, a section of the electrospun membrane, measuring “4 cm × 4 cm”, was excised to serve as the electronegative tribolayer within the TENG assembly. As a result of these preparations, the calculated weight of the Cu-PCN material amounted to 0.68 mg. As shown in Supplementary Table 5, the CO production rate in the air is 22.44 nmol h-1, equaling a yield of 33 μmol g-1 h-1. Furthermore, μmol g-1 is used to measure and compare CO2 conversion capacity. The “μmol” in the unit corresponds to the CO production, whereas “g” pertains to the loading of the single-atom catalyst Cu-PCN.

DFT calculations

All the DFT calculations were performed with the Perdew-Burke-Ernzerhof functional under the generalized gradient approximation65,66 for the exchange-correlation interaction, as implemented in the Vienna Ab initio Simulation Package (VASP)67,68. A cutoff kinetic energy of 450 eV was applied to expand the electronic wave functions and the projector augmented-wave method was adopted to describe the electron-core interaction. A “3 × 3” PCN model with a Gamma-centered “3 × 3 × 1” k-mesh was used for the structural optimization. For the interaction between CO2 and quaternized CNF, it was calculated with Gaussian69. The charge density difference of the CO2/Cu-PCN system was calculated by \(\Delta {{{{{\rm{\rho }}}}}}={{{{{{\rm{\rho }}}}}}}_{{{{{{\rm{total}}}}}}}-{{{{{{\rm{\rho }}}}}}}_{{{{{{{\rm{CO}}}}}}}_{2}}-{{{{{{\rm{\rho }}}}}}}_{{{{{{\rm{Cu}}}}}}-{{{{{\rm{PCN}}}}}}}\), where \({{{{{{\rm{\rho }}}}}}}_{{{{{{\rm{total}}}}}}}\) is total charge density of the whole system, and \({{{{{{\rm{\rho }}}}}}}_{{{{{{{\rm{CO}}}}}}}_{2}}\) and \({{{{{{\rm{\rho }}}}}}}_{{{{{{\rm{Cu}}}}}}-{{{{{\rm{PCN}}}}}}}\) charge densities of the CO2 molecule and Cu-PCN, respectively.

Sample characterization

The surface morphology of the samples was characterized using JEOL JSM-6710F field emission scanning electron microscope (FE-SEM). Transmission Electron Microscope (TEM) images were obtained using a TECNAI G2 TF20 high-resolution transmission electron microscope at 200 kV operating voltage (FEI, USA). At the same time, STEM-map** images were captured with the equipped Energy Dispersive X-Ray Spectroscopy (EDX) accessory. Aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) measurements were conducted on a Thermo Scientific Themis Z instrument. X-ray absorption spectroscopy (XAS) measurements were performed at the XAS beamline at the Australian Synchrotron (ANSTO) in Melbourne operated at 3.0 GeV. Liquid nitrogen cooled Si (111) double crystals were used as the double-crystal monochromator, which could cover the photon energy ranging from 5 to 19 KeV. The output voltage was measured by using NI PCIe-6259 DAQ card (National Instruments) with a load resistance of 100 MΩ, while the short-circuit current (Isc) was measured by using an SR570 low-noise current amplifier (Stanford Research System). During the electrical output test of the TENGs, an impact force of 5 N was maintained, and the frequency was 5 Hz. In order to prevent the possible influence of copper wires on CO2RR, all wire clips were sealed. Fourier transform infrared spectroscopy (FTIR) spectra of CNF films were recorded on an FTIR spectrometer (Nicolet 6700, Themo Fisher Scientific Inc) from 4000 cm-1 to 400 cm-1 at a resolution of 4 cm-1 with the temperature of 100 °C to ensure the free water evaporated from the surface of the quaternized CNF film. CO2 adsorption/desorption measurement were performed on a TG-MS analyzer (TA Q600- HIDEN HPR 20). Before measurement, the sample was activated by heating at 200 °C for 2 h under an Ar steam. After the furnace temperature was cooled and stabilized at 35 °C, the gas was switched to the 50% CO2 and 50% N2 (volume percentage) mixture gas for adsorption. After 2 h, the temperature then was increased to 200 °C with a rate of 20 °C min-1 under an Ar steam and kept for 2 h for desorption. CO2/N2 selectivity was determined according to the ratio of the integral area of CO2 to that of N2, recorded by MS. Thermogravimetric analyses (TGA) were carried out with a TA Q5000 (V3.15 Build 263) thermogravimetric analyzer. The test was carried out under a nitrogen atmosphere, and the temperature was raised from 40 to 600 °C at a rate of 10 °C min-1. A zirconia oxygen analyzer (ZO-2000) with a resolution of 0.1 ppm was employed to analyze the mixed gas post-reaction. The gas from the reaction was drawn into a gas sampling bag using a micro vacuum self-priming pump, and subsequently, it was directed into the inlet of the oxygen detector. After stabilizing the flow indicator, the oxygen concentration was recorded. The products from CO2RR were analyzed by gas chromatography (GC) analysis. Gaseous products were collected from the flow gas every 1 h, and 1 mL of the collected gas was analyzed by GC (8890, Agilent) equipped with FID and TCD detectors and argon (99.999%) as the carrier gas. Isotope measurements for CO2RR were performed on an Agilent 7890 A GC-5975C MS. Selected ion monitoring (SIM) mode was used to detect the presence of 13CO (m/z = 29) in the samples. The temperature-programmed carbon dioxide desorption (CO2-TPD) was performed on a Quantachrome autosorb-iQ instrument. The sample was first pretreated in a He flow at 150 °C for 30 min, followed by cooling to 40 °C. Then, the sample adsorbed CO2 for 60 min in a CO2 flow. CO2 desorption was conducted from 50 to 270 °C with a rate of 10 °C min-1, and CO2 was collected by a mass spectrometer. The CO2 adsorption experiment at normal temperature and pressure was tested on BSD-VVS. The amount and speed of adsorption and desorption of the sample to CO2 vapor with different CO2 contents were determined by weighing the weight change of the sample before and after adsorption and desorption with a microbalance. The breakthrough experiments were carried out in a vertical fixed-bed reactor with ambient air feed in a down-flow manner. The concentration of the CO2 in the outlet stream was monitored with a Vaisala GMP343 CO2 probe (0–400 ppm of CO2 is the measurement range). In wind-driven TENG-catalyzed CO2RR, the flow rate of gaseous was measured using an anemometer (UT363).