Hydriding and dehydriding characteristics of LiBH4 and transition metals-added magnesium hydride

Abstract

In this study, MgH2 was used as a starting material instead of Mg. Ni, Ti, and LiBH4 with a high hydrogen-storage capacity of 18.4wt% were added. A sample with a composition of MgH2–10Ni–2LiBH4–2Ti was prepared by reactive mechanical grinding. The activation of MgH2–10Ni–2LiBH4–2Ti was completed after the first hydriding–dehydrding cycle. The hydriding rate decreases as the temperature increases due to the decrease in the driving force for the hydriding reaction. At the 1st cycle, the sample desorbs 1.45wt% H for 10min, 2.54wt% H for 20min, 3.13wt% H for 30min, and 3.40wt% H for 60min at 593K under 1.0bar H2. At the 2nd cycle, the sample absorbs 3.84wt% H for 5min, 3.96wt% H for 10min, and 4.05wt% H for 60min at 593K under 12bar H2. MgH2–10Ni–2LiBH4–2Ti after reactive mechanical grinding contained MgH2, Mg, Ni, TiH1.924, and MgO phases. The reactive mechanical grinding of Mg with Ni, LiBH4, and Ti is considered to create defects on the surface and in the interior of Mg (to facilitate nucleation), and to reduce the particle size of Mg (to shorten diffusion distances of hydrogen atoms). The formation of Mg2Ni during hydriding–dehydriding cycling increases the hydriding and dehydriding rates of the sample.