Formation and Hydrogen Storage Properties of Dual-Cation (Li, Ca) Borohydride

Lithium borohydride, LiBH4, possesses high hydrogen capacity, but cannot be used for hydrogen storage owing to the problematic H-exchange kinetics and thermodynamics. In the present study, we employed the Li+−Ca2+ combination strategy to improve the de/rehydrogenation properties of LiBH4. Our study found that mechanically milling 1:1 LiBH4/Ca(BH4)2 mixture formed a dual-cation borohydride, Li0.9Ca(BH4)2.9, which then transformed to stoichiometric LiCa(BH4)3 in the heating process. The formation and decomposition behaviors of LiCa(BH4)3 were studied using X-ray diffraction and thermogravimetry/differential scanning calorimetry/mass spectroscopy techniques. It was found that LiCa(BH4)3 differs significantly from the component phases in terms of physical properties, decomposition behaviors, and mechanistic pathway. In particular, LiCa(BH4)3 exhibits improved de/rehydrogenation properties relative to the component phases. These experimental findings exemplified the effectiveness of manipulation of dual-cation combination in tuning the de/rehydrogenation properties of the ionic light-metal borohydrides.