Comparison of Hydrogen Storage Properties of Pint MgH2 and Pure Mg

At the first cycle (n=1), pure MgH2 absorbed hydrogen extremely slowly at 593 K under 12 bar H-2, absorbing 0.04 wt% H for 60 min. Activation of the pure MgH2 was completed after five hydriding-dehydriding cycles. At the 6th cycle, the pure MgH2 absorbed 2.41 wt% H for 5 min, 3.00 wt% H for 10 min, and 4.21 wt% H for 60 min, showing that the activated pure MgH2 had a much higher hydriding rate than the activated pure Mg. The pure Mg absorbed 0.10 wt% H for 5 mm, 0.38 wt% H for 30 min, and 0.51 wt% H for 60 min at the first cycle. The activated pure Mg, whose activation was also completed after five hydriding-dehydriding cycles, absorbed 1.76 wt% H for 5 min, 2.17 wt% H for 10 mm and 3.40 wt% H for 60 mm. The XRD pattern of the pure MgH2 after hydriding-dehydriding cycling (n=7) revealed that the sample contained Mg, a small amount of MgO, and a large amount of MgH2, showing that a large fraction of MgH2 remains even after dehydriding in vacuum at 623 K for 2 h.