Modifying hydrogen storage properties of the RE−Mg-based alloys with minor Sc addition

Abstract

To address the challenges posed by high reaction temperatures and the slow kinetics of Mg-based alloys with high hydrogen storage density, Mg−RE−TM (RE = rare earth, TM = metallic element) alloys have been extensively researched and hold great promise. In this study, a series of Mg−RE−TM based Mg₉₀Y₂Ce₂Ni₃Al_3-xSc_x (x = 0, 0.3, 0.6, 0.9, 1.2) alloys were prepared. The addition of Sc element has been found to enhance the activation and kinetic properties of the alloy. Compared with the significant differences in the first four dehydrogenation curves of the Sc0 sample, the first activated dehydrogenation curve of the Sc1.2 alloy overlaps with the fully activated dehydrogenation curve. The dehydrogenation activation energy decreased from 96.56 kJ/mol in the Sc0 alloy to 63.69 kJ/mol in the Sc0.9 alloy. Through analysis of the microstructure, phase composition, and hydrogen absorption and desorption kinetics of the alloy, the mechanisms for improving the hydrogen storage properties of the alloy were elucidated. The nucleation-growth-impingement Avrami model was employed to accurately simulate the hydrogen storage kinetics. The results showed that stage II was prolonged and accelerated at high temperature, and the growth rate and hydrogen storage of stage I were increased at low temperature in hydrogen absorption. Microstructure analysis revealed the presence of Mg, CeMg₁₂, Mg₄₇Y, and YNi₂Al₃ phases in the Sc0 sample. Upon the addition of Sc element, a new phase, ScNiAl, was formed, and the coarse grain size of the main phase was significantly refined. This refinement provides faster diffusion channels for hydrogen atoms, accelerating the phase transition between Mg alloys and hydrides. The microstructure changes explain the improved activation properties, effective hydrogen absorption and desorption capacity, and kinetic properties of the Mg-based samples.