Effect of LiH on hydrogen storage property of MgH2

Recent works showed that the addition of LiBH₄ significantly improves the sorption kinetics of MgH₂, and LiH decomposed from LiBH₄ was supposed to play the catalytic effect on MgH₂. In order to clarify this mechanism, the effect of LiH on the hydriding/dehydriding kinetics and thermodynamics of MgH₂ was systematically investigated. The hydrogenation kinetics of LiH-doped samples, as well as the morphology after several cycles, was similar to those of pure MgH₂, which indicate that Li⁺ had no catalytic effect on the hydrogenation of Mg. Moreover, the addition of LiH strongly retarded the hydrogen desorption of MgH₂ doped with/without Nb₂O₅, and resulted in higher starting temperature of desorption, larger activation energy and larger pressure hysteresis of PCI curves of MgH₂. H₂, HD and D₂ were observed in the desorption products of MgH₂-2LiD, which confirms that H–H exchange indeed occurs between MgH₂ and LiH, hence deteriorate desorption kinetics/thermodynamics of MgH_2. The results implied that the additives containing H⁻ could retard the hydrogen desorption of MgH₂ by H–H exchange effect.