Synthesis of a ternary amide Li K (NH2) and a novel Li3K(NH2)4–xMgH2 combination system for hydrogen storage

Abstract

Abstract The ternary amides LiK2(NH2)3, LiK(NH2)2, and Li3K(NH2)4 are successfully synthesized by ball milling mixtures of LiNH2 and KNH2, and the hydrogen storage properties of Li3K(NH2)4–xMgH2 (x = 1, 2, 3, 4) are systematically investigated. The Li3K(NH2)4–2MgH2 sample displays optimized hydrogen storage properties, releasing 6.37 wt% of hydrogen in a two-stage reaction with an onset temperature of 60 °C. The first dehydrogenation stage exhibits good reaction kinetics and thermodynamic properties because of a lower activation energy and appropriate enthalpy change. After full dehydrogenation at 130 °C, the Li3K(NH2)4–2MgH2 sample absorbs 3.80 wt% of H2 below 160 °C in a variable temperature hydrogenation mode. Mechanistic investigations indicate that Li3K(NH2)4 reacts with MgH2 to produce Mg(NH2)2, LiH, and KH during ball milling. In the heating process, Mg(NH2)2 first reacts with LiH to form Li2Mg2N3H3 and LiNH2, while KH works as a catalyst, and then, KH reacts with Li2Mg2N3H3 and LiNH2 to generate a new K-containing compound.