Hydrogen-Storage Properties of Ni and LiBH4-Added MgH2.

In this work, MgH2 was employed as a starting material instead of Mg used in our previous work. Ni and LiBH4, which can absorb 18.4 wt% of hydrogen, were added. A sample with a composition of 86 wt% MgH2 + 10 wt% Ni + 4 wt% LiBH4 (named MgH2-10Ni-4LiBH4) was prepared by milling under hydrogen (reaction-involved milling) and its hydrogen-storage properties were examined. In addition, the rate-limiting step for the dehydriding reaction of the sample at the first cycle was analyzed. The activation of MgH2-10Ni-4LiBH4 for hydriding and dehydriding reactions was not required. The as-milled sample absorbed and released nearly 5 wt% H at 623 K for 60 min; it absorbed 4.90 wt% H under 12 bar H2 for 20 min and released 4.94 wt% H under 1.0 bar H2 for 60 min. The hydriding rate exhibited an inverse dependence on temperature. This is due to a decrease in the driving force for the hydriding reaction (the difference between the applied hydrogen pressure and the equilibrium plateau pressure) with the increase in temperature.