Amorphous-versus big cube- Zr₂Ni for improving the kinetics of hydrogenation/dehydrogenation behaviors for MgH₂ powders

Whereas all catalytic materials used to improve the behaviors of hydrogenation/dehydrogenation kinetics for MgH₂ have long-range order structure, the present work proposes two different types of structure; i.e. short range- and medium range- order. For the purpose of the present study, ultrafine powders of amorphous- and big cube-Zr₂Ni phases were prepared by ball milling small bulk pieces of tetragonal-Zr₂Ni alloy prepared by arc melting technique. Small volume fraction (10 wt. %) of amorphous and big-cube powders obtained after ball milling for 100 and 150 h, respectively were individually mixed with as-synthesized MgH₂ powders and then ball milled for 50 h. The results have shown that nanocomposite MgH₂/10 wt.% metallic glassy Zr₂Ni powders had high density of hydrogen (∼6 wt.%) and possessed fast kinetics of hydrogen uptake/release at 250 °C within 1.15 and 2.5 min, respectively. Whereas, MgH₂/10 wt.% of big cube Zr₂Ni nanocomposite showed moderate improvement on hydrogenation (1.8 min)/dehydrogenation (7 min) kinetics due to the heterogeneous distribution of their particles onto the MgH₂ powders.