The hydrogen absorption and release properties of oxide-added alloys (90Mg + 10Fe2O3 and 90Mg + 10MnO) and halideaddedalloys (90Mg + 10TiCl3 and 90Mg + 10TaF5), which were prepared by high-energy ball milling in hydrogen (reactivemechanical grinding), were compared after activation. In addition, the hydrogen absorption and release properties of95Mg + 5TiCl3, which had high hydrogen absorption and release rates, were investigated in detail. A halide-added Mg alloy,90Mg + 10TiCl3, had better hydrogen absorption and release properties than the oxide-added Mg alloys, 90Mg + 10Fe2O3 and90Mg + 10MnO. 95Mg + 5TiCl3 had a relatively high effective hydrogen-storage capacity of about 6.3 wt% and a relativelyhigh hydrogen release rate. At the first cycle (n = 1), the sample absorbed 4.84 wt% H for 5 min, 5.86 wt% H for 10 min, and6.27 wt% H for 60 min at 593 K in 12 bar H2. The activation of the sample was completed after three hydrogen absorptionreleasecycles. At the third cycle (n = 3), the sample released 1.26 wt% H for 10 min, 3.52 wt% H for 30 min, and 5.32 wt% Hfor 60 min at 593 K in 1.0 bar H2. The XRD pattern of 95Mg + 5TiCl3 dehydrided at n = 4 revealed Mg, β-MgH2, and smallamounts of MgO and TiH1.924. The formation of titanium hydride (TiH1.924) in 95Mg + 5TiCl3 is believed to have contributedto the improvement of hydrogen absorption and release properties of 95Mg + 5TiCl3.

Keywords: Hydrogen absorbing materials, Reactive mechanical grinding, Microstructure, Phase transformation, Oxide and halide addition to Mg