Improved Hydrogen Storage Properties of LiBH4 Destabilized by in Situ Formation of MgH2 and LaH3

A reactive composite of LiBH4–xLa2Mg17 was successfully prepared by means of mechanochemical reaction under 40 bar of H2. It was found that MgH2 and LaH3 were readily formed in situ during high-pressure ball milling, and a strong dependency of hydrogen storage performance of the LiBH4–xLa2Mg17 composites on the content of La2Mg17 was observed. The as-prepared LiBH4–0.083La2Mg17 composite under 40 bar of H2 exhibits superior hydrogen storage properties as ∼6.8 wt % of hydrogen can be reversibly desorbed and absorbed below 400 °C. It was also purposed that the self-decomposition of MgH2 first occurred to convert into Mg with hydrogen release upon dehydrogenation and subsequently catalyzed the reaction of LiBH4 and LaH3 to liberate additional hydrogen along with the formation of LaB6 and LiH. The in situ formed MgH2 and LaH3 provide a synergetic thermodynamic and kinetic destabilization on the de/hydrogenation of LiBH4, which is responsible for the distinct reduction in the operating temperatures of the as-prepared LiBH4–xLa2Mg17 composites.