Hydrogen storage kinetics of La- and Sc-doped Mg-Ni alloys

Magnesium-based hydrogen storage materials offer advantages such as high hydrogen storage capacity and low cost, but the high stability of their hydrides and slow hydrogen desorption rate remain bottlenecks restricting their further development. This study employs doping with different rare earth elements to investigate the effects of the distinct existing forms and action mechanisms of RE elements Sc and La in Mg-Ni alloys on hydrogen de−/absorption performances. The results demonstrate that Sc exhibits a stronger binding force with Ni, leading to the formation of a new Ni₂Sc phase in the microstructure, while La forms the La₂Mg₁₇ phase with Mg. After hydrogenation, the highly stable Ni₂Sc no longer reacts with hydrogen, whereas La₂Mg₁₇ undergoes in-situ hydrogen-induced transformation to form MgH₂ and nano-sized LaH_x phases. In Sc containing alloy, Ni₂Sc promotes hydrogen dissociation and exerts a significant enhancement effect on the hydrogen absorption process. At 270 °C, a hydrogen absorption capacity of 5.04 wt% is achieved within 1 min. La containing alloy can completely release hydrogen at 270 °C in 10 min. The nano-sized LaHₓ catalytic phase accelerates hydrogen transport through its strong attraction to hydrogen, and the numerous interfaces of the dispersed phase also provide abundant channels for hydrogen diffusion. Geometric micro-stress analysis reveals a distinct stress between LaH_x and the matrix, which reduces the external energy required for the reaction and lowers the activation energy to 71.9 kJ/mol.