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.