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

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)-xMgH(2) (x = 1, 2, 3, 4) are systematically investigated. The Li3K(NH2)(4)-2MgH(2) sample displays optimized hydrogen storage properties, releasing 6.37 wt% of hydrogen in a two-stage reaction with an onset temperature of 60 degrees 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 degrees C, the Li3K(NH2)(4)-2MgH(2) sample absorbs 3.80 wt% of H-2 below 160 degrees 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. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.