Abstract
The addition of different metal hydrides to Li–N–H system offers a possible way to modify its thermodynamic properties and/or the dehydrogenation/hydrogenation kinetics. In this paper we report the hydrogen storage properties of LiNH2–LiH system with MH2 added (M = Mg, Ca, Ti) and clarify the chemical interactions occurring during hydrogen cycling. Detailed structural investigations reveal that during heating under hydrogen, MH2 (M = Mg, Ca) reacts with LiNH2 to form Li2Mg(NH)2 and 2CaNH–Ca(NH2)2 solid solution, with simultaneous hydrogen release. Formation of the Li2NH–CaNH mixture after dehydrogenation of the LiNH2–LiH with CaH2 added is proved by XRPD and FTIR, providing a new reversible pathway for hydrogen storage in the Li–Ca–N–H system. Notable improvement in the dehydrogenation temperature and kinetics was observed for LiNH2–LiH system with CaH2 and MgH2 added, without clear effects in the case of TiH2. The kinetic analysis reveals that dehydrogenation process is diffusion-controlled and the beneficial effect of MgH2 and CaH2 is due to the enhancement of Li+ mobility.
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