Improvement of hydrogen-storage properties of MgH_2 by Ni,LiBH_4, and Ti addition

摘要

In this work, differently from our previous work, MgH_2 instead of Mg was used as a starting material. Ni, Ti, and LiBH_4 with a high hydrogen-storage capacity of 18.4 wt% were added. A sample with a composition of MgH_2-10Ni-2LiBH_4-2Ti was prepared by reactive mechanical grinding. MgH_2-10Ni-2LiBH_4-2Ti after reactive mechanical grinding contained MgH_2, Mg, Ni, TiH_(1.924), and MgO phases. The activation of MgH_2-10Ni-2LiBH_4-2Ti for hydriding and dehydriding reactions was not required. At the number of cycles, n = 2, MgH_2-10Ni-2LiBH_4-2Ti absorbed 4.09 wt% H for 5 min, 4.25 wt% H for 10 min, and 4.44 wt % H for 60 min at 573 K under 12 bar H_2. At n = 1, MgH_2-10Ni-2LiBH_4-2Ti desorbed 0.13 wt % H for 10 min, 0.54 wt% H for 20 min, 1.07 wt% H for 30 min, and 1.97 wt% H for 60 min at 573 K under 1.0 bar H_2. The PCT (Pressure-Composition-Temperature) curve at 593 K for MgH_2-10Ni-2LiBH_4-2Ti showed that its hydrogen-storage capacity was 5.10 wt%. The inverse dependence of the hydriding rate on temperature is partly due to a decrease in the pressure differential between the applied hydrogen pressure and the equilibrium plateau pressure with the increase in temperature. The rate-controlling step for the dehydriding reaction of the MgH_2-10Ni-2LiBH_4-2Ti at n = 1 was analyzed.