Hydrogen Pressure-Dependent Dehydrogenation Performance of the Mg(NH₂)₂–2LiH–0.07KOH System

The Mg(NH2)2–2LiH system with KOH additive is a promising high-capacity hydrogen storage material in terms of low dehydrogenation temperatures, good reversibility, and excellent cycling stability. Various mechanisms have been reported to elucidate the reasons for the K-containing additive improving the hydrogen storage performance. Herein, the dehydrogenation performance of Mg(NH2)2–2LiH–0.07KOH is found to be strongly associated with hydrogen pressures. The Li2K(NH2)3 and KH produced from the reaction between KOH, LiH, and Mg(NH2)2 in the ball milling process are converted into Li3K(NH2)4, MgNH, and LiNH2 in the heating dehydrogenation process under Ar carrier gas or very low hydrogen pressure, exhibiting a two-peak dehydrogenation process. For the sample under high hydrogen pressure, Li2K(NH2)3 can react with LiH to convert into Li3K(NH2)4 and further to form KH and LiNH2 in the heating process, showing a one-peak dehydrogenation process under 5 bar hydrogen. The hydrogen pressure-dependent reactions of K-containing additives in the Mg(NH2)2–2LiH system lead to a different hydrogen storage performance under different dehydrogenation conditions.