Hydrogen storage thermodynamic and kinetic characteristics of PrMg₁₂-type alloys synthesized by mechanical milling

Abstract

To improve the hydrogen storage performance of PrMg₁₂-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMg₁₁Ni+x wt. % Ni (x = 100, 200) alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were investigated by X-ray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry (DSC) and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5.572 wt. % for the x = 100 alloy and 5.829 wt. % for the x = 200 alloy, respectively. The enthalpy change (ΔH), entropy change (ΔS) and the dehydrogenation activation energy ($E_{\rm{k}}^{{\rm{de}}}$) markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.