Oxide-added samples, 90 wt% Mg + 10 wt% Fe2O3 (named Mg-10Fe2O3) and 90 wt% Mg + 10 wt% MnO (named Mg- 10MnO), a halide-added sample, 90 wt% Mg + 10 wt% VCl3 (named Mg-10VCl3), and a pure Mg sample (named Mg) were prepared by reaction-involving grinding (grinding in hydrogen). The hydriding and dehydriding properties of the prepared samples were examined and compared. For the halide-added sample, Mg-10VCl3, the initial hydriding rate was much higher and the quantity of hydrogen absorbed for 60 min was significantly larger than those of the oxide-added samples and Mg. After activation, Mg-10VCl3 had much higher initial hydriding and dehydriding rates, and much larger quantities of hydrogen absorbed and released for 60 min, than Mg-10Fe2O3, Mg-10MnO, and Mg. The activated Mg-10Fe2O3 and Mg-10MnO absorbed 5.16 and 3.95 wt% H, respectively, at 593 K in 12 bar H2 for 60 min. The activation of Mg-10VCl3 was completed after two hydriding-dehydriding cycles. Mg-10VCl3 had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of 5.71 wt% at the second cycle (n = 2). At n = 2, the sample absorbed 4.58 wt% H for 5 min and 5.71 wt% H for 60 min at 593 K in 12 bar H2. At n = 3, the sample released 1.32 wt% H for 10 min and 5.42 wt% H for 60 min at 593 K in 1.0 bar H2. The hydrogen release equilibrium hydrogen pressure-composition-temperature (PCT) curve at 593 K showed an equilibrium plateau pressure at 2.56 bar.

Keywords: Hydrogen absorbing materials, Reaction-involving grinding, Scanning electron microscopy (SEM), X-ray diffraction, MnO, Fe2O3, VCl3 addition.