High capacity multicomponent hydrogen storage materials: Investigation of the effect of stoichiometry and decomposition conditions on the cycling behaviour of LiBH4–MgH2

LiBH₄–MgH₂ is an attractive reversible hydrogen storage system, it combines two high capacity hydrides (18.3 and 7.6 wt.%, respectively) and the concerted dehydrogenation reaction has a smaller enthalpy change than either species on its own. The latter effect leads to a destabilisation of the hydrided products and results in a lowering of the dehydrogenation temperature. In situ neutron diffraction experiments have been undertaken to characterise the mechanism of decomposition of the LiBD₄–MgD₂ system, with an emphasis on investigating the synergistic effects of the components during cycling under various conditions. This study compares the effect of stoichiometry of the multicomponent system on the cycling mechanism. Results show that LiBD₄–MgD₂ in a 2:1 molar ratio can be reversibly dehydrogenated under low pressures of hydrogen or under vacuum, contrary to earlier reports in the literature, although the reaction was only partially reversed for the 2:1 mixture decomposed under vacuum. This work shows that the reaction pathway was affected by dehydrogenation conditions, but the stoichiometry of the multicomponent system played a minor role.