Effect of LiH on hydrogen storage property of MgH2

• Effect of LiH on the H-sorption properties of MgH2 was investigated.
• The addition of LiH can deteriorate the desorption kinetics/thermodynamics of MgH2.
• H–H exchange was observed between LiH and MgH2.
• The negative effect of LiH might be due to H–H exchange between LiH and 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 MgH2. The results implied that the additives containing H− could retard the hydrogen desorption of MgH2 by H–H exchange effect.