In-situ formation of uniform Mg2Ni catalyst and hydrogen storage properties of Mg-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 degrees C, and complete decomposition can be achieved in 2.4 min at 300 degrees 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 selfrefinement, 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.