A Novel Li–Ca–B–H Complex Borohydride: Its Synthesis and Hydrogen Storage Properties

Abstract

The synthesis and hydrogen-storage properties of the mixed alkali metal and alkaline-earth metal borohydride are systematically investigated. It is found that mechanical milling a mixture of LiBH4 and CaCl2 with molar ratio of 3:1 in tetrahydrofuran (THF) forms a new LiBH4·Ca(BH4)2·2THF compound. Thermal analysis indicates that the decomposition process of the new compound involves four steps: (1) LiBH4·Ca(BH4)2·2THF decomposes first into high temperature phase of LiBH4, CaB6, and an intermediate phase Ca–B–H–Cl hydride and synchronously releases a large number of H2 and THF gas together with less B2H6; (2) the eutectic melting of LiBH4 and Ca–B–H–Cl hydride; (3) Ca–B–H–Cl hydride decomposes into CaHCl, CaB6, and a little H2; (4) LiBH4 reacts with CaHCl, generating H2, CaH2, CaB6, LiH, and LiCl. The first dehydrogenation step starts at ca. 70 °C, which is much lower than that of the pristine LiBH4 and Ca(BH4)2. According to Kissenger’s equation, the activation energies of the different dehydrogenation ste...