Controllable decomposition of Ca(BH4)2 for reversible hydrogen storage.

Ca(BH4)2 could reversibly store 9.6 wt% hydrogen based on the overall reaction of Ca(BH4)2 → 1/3CaB6 + 2/3CaH2 + 10/3H2. Formation of CaB6 instead of elemental boron and/or high boranes (e.g. CaB12H12) in the dehydrogenation process is crucial for rehydrogenation. Here, we reported two experimental protocols regarding how to form CaB6 from the decomposition of Ca(BH4)2: (1) decomposition below the melting point, e.g. 350 °C via CaB2H6 to CaB6 and (2) decomposition above the melting point, e.g. 400 °C via elemental boron to CaB6.