Synthesis of a ternary amide LixKy(NH2)x+y and a novel Li3K(NH2)4–xMgH2 combination system for hydrogen storage

摘要

cqvip:The ternary amides LiK2(NH2)3, LiK(NH2)2, and Li3 K(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)4–2 Mg H2 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)4–2 MgH2 sample absorbs 3.80 wt% of H2 below 160 °C in a variable temperature hydrogenation mode. Mechanistic investigations indicate that Li3 K(NH2)4 reacts with Mg H2 to produce Mg(NH2)2, LiH,and KH during ball milling. In the heating process, Mg(NH2)2 first reacts with Li H to form Li2 Mg2 N3 H3 and Li NH2, while KH works as a catalyst, and then, KH reacts with Li2Mg2N3H3 and Li NH2 to generate a new K-containing compound.