Development of Mg-oxide-Ni hydrogen-storage alloys by reactive mechanical grinding

Mg-oxide and Mg-oxide-Ni hydrogen storage alloys were prepared by mechanical grinding under H2 (reactive mechanical grinding). Among these alloys, Mg-(7.5wt%Fe2O3, 7.5 wt%Ni) prepared by grinding for 4 h with nano-structured Fe2O3 particles and Ni showed the best hydrogen storage properties. The as-milled sample absorbed 4.75 wt% H at 593 K under 12 bar H2 for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.36 wt% H at 593 K under 12 bar H2 for 60 min and desorbed 4.26 wt% H at 593 K under 1.0 bar H2 for 60 min. After hydriding-dehydriding cycling, Mg2Ni, Fe and MgO are formed. The large bar-like hydrided particles have round and expanding surfaces, suggesting that they expanded during the hydriding reaction, while the dehydrided particles exhibit contracted surfaces with wrinkles.