Mg-oxide and Mg-oxide-Ni hydrogen storage alloys, 90 wt% Mg + 10 wt% Fe2O3 (named Mg-10Fe2O3), 90 wt% Mg + 5 wt% Fe2O3 + 5 wt% MnO (Mg-5Fe2O3-5MnO), 90 wt% Mg + 3.3 wt% Fe2O3 + 3.3 wt% Ni + 3.3 wt% MnO (Mg-3.3Fe2O3-3.3Ni- 3.3MnO), and 90 wt% Mg + 5 wt% Fe2O3 + 5 wt% Ni (Mg-5Fe2O3-5Ni), were prepared by mechanical milling under H2 (reaction-involved milling). The hydrogen storage properties of the prepared alloys were then investigated. Among these samples, Mg-5Fe2O3-5Ni had the largest quantities of the hydrogen absorbed for 60 min at the first cycle and released for 60 min after activation, the highest initial hydriding rate at the first cycle, and the highest initial dehydriding rate after activation. The as-milled Mg-5Fe2O3-5Ni absorbed 1.75 wt%H for 2.5 min, 2.98 wt%H for 10 min, 3.82 wt%H for 30 min, and 4.24 wt%H for 60 min at 593 K under 12 bar H2. The activated Mg-5Fe2O3-5Ni released 1.70 wt%H for 10 min, 3.12 wt%H for 30 min, and 3.69 wt%H for 60 min at 603 K under 1.0 bar H2. Fe2O3 was reduced to Fe and Mg was oxidized to MgO, due to the large difference in the chemical affinities of Fe and Mg for oxygen.

Keywords: H2-storage properties of Mg, Mg-Oxide-Ni alloys, Reaction-involved milling, Hydriding and dehydriding rates, Phase transformation.