Reversible hydrogen storage in LiBH4/Ca(AlH4)2 systems

To improve the hydrogen storage property of LiBH4, the LiBH4/Ca(AlH4)2 reactive systems with various ratios were constructed, and their de-/hydrogenation properties as well as the reaction mechanisms were investigated experimentally. It was found that the sample with the LiBH4 to Ca(AlH4)2 molar ratio of 6:1 exhibits the best comprehensive hydrogen storage properties, desorbing hydrogen completely (8.2 wt.%) within 35 min at 450 °C and reversibly absorbing 4.5 wt.% of hydrogen at 450 °C under a hydrogen pressure as low as 4.0 MPa. During the first dehydrogenation process of the LiBH4/Ca(AlH4)2 systems, the CaH2 and Al particles were in situ precipitated via the self-decomposition of Ca(AlH4)2, and then reacted with LiBH4 to form CaB6, AlB2 and LiH. Whereafter, the sample can cycle between LiBH4 + Ca(BH4)2 + Al in the hydrogenated state and CaB6 + AlB2 + LiH in the dehydrogenated state.

► The hydrogen storage property of LiBH4 can be improved by combining with Ca(AlH4)2.
► The LiBH4/Ca(AlH4)2 (6:1) system exhibits the best comprehensive property.
► 4.5 wt.% of hydrogen can be reabsorbed at 450 °C under 4.0 MPa hydrogen pressure.
►  LiBH4 and Ca(BH4)2 can be formed upon hydrogenation.