LiBH 4 , as a potential material with the highest reversible hydrogen storage capacity for hydrogen vehicle applications, has always been hydrogenated and dehydrogenated in the liquid state. In this study, we demonstrate, for the first time, that 8.3 wt % hydrogen uptake can be obtained from the LiBH 4 + MgH 2 system in the solid state through nanoengineering and mechanical activation. Hydrogen release, although slower than uptake, can also be attained in the solid state. All of these enhancements are achieved without any catalysts, which underscores the effectiveness of nanoengineering and mechanical activation as well as the opportunity for further improvements in the future.

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The LiBH4 + MgH2 system has great potential in reversible hydrogen storage for fuel cell vehicles. However, it has always been dehydrogenated and rehydrogenated in the liquid state until recently. The solid-state hydriding and dehydriding are necessary in order to achieve hydrogen uptake and release near ambient temperature. In this study, the solid-state hydriding mechanism of 2LiH + MgB2 mixtures has been investigated. It is found that the solid-state hydriding proceeds in two elementary steps. The first step is the ion exchange between the Mg2+ and Li+ ions in the MgB2 crystal to form an intermediate compound (Mg1−x Li2x )B2. The second step is the continuous ion exchange and simultaneous hydrogenation of (Mg1−x Li2x )B2 to form LiBH4 and MgH2. This finding is consistent with the observed diffusion-controlled hydriding kinetics.

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