In-situ formation of uniform Mg₂Ni catalyst and hydrogen storage properties of Mg[sbnd]41Ni alloys with varied grain sizes and morphologies

In order to clarify the cyclic microstructure evolution process and the influence of grain size on the hydrogen de−/absorption properties of magnesium-based alloys. Mg-41 wt%Ni (Mg41Ni) alloys with varying grain sizes were prepared using different solidification rates. By analyzing the cross sections of ball-milled particles, it is found that the amorphous layer generated during ball milling is not conducive to the activation stage. Additionally, the coarse primary Mg₂Ni and the lamellar Mg₂Ni in the eutectic break into smaller Mg₂Ni particles during the hydrogen absorption and release cycles. Thus, the fast solidified alloys can absorb 2.1 wt% of hydrogen gas at 125 °C, and complete decomposition can be achieved in 2.4 min at 300 °C. The activation energy of dehydrogenation decreases from 93.2 kJ/mol for slow solidification to 85.9 kJ/mol for fast solidification. Different kinetic models are used to fit and investigate the rate-controlling process of hydrogen desorption. The activated sample consists of the Mg matrix and uniformly distributed fine Mg₂Ni particles due to the self-refinement, which significantly shortens the diffusion distance of H atoms. Besides, the multitude of pores generated inside the particles also facilitate the ingress and outflow of hydrogen.