A novel aided-cation strategy to advance the dehydrogenation of calcium borohydride monoammoniate

Abstract

The crystal structure of a promising hydrogen storage material, calcium borohydride monoammoniate (Ca(BH4)2·NH3), is reported. Structural analysis revealed that this compound crystallizes in an orthorhombic structure (space group Pna21) with unit-cell parameters of a = 8.4270 A, b = 12.0103 A, c = 5.6922 A and V = 576.1121 A3, in which the Ca atom centrally resides in a slightly distorted octahedral environment furnished by five B atoms from BH4 units and one N atom from the NH3 unit. As Ca(BH4)2·NH3 tends to release ammonia rather than hydrogen when heated in argon, a novel aided-cation strategy via combining this compound with LiBH4 was employed to advance its dehydrogenation. It shows that the interaction of the two potential hydrogen storage substances upon heating, based on a promoted recombination reaction of BH and NH groups, enables a significant mutual dehydrogenation improvement beyond them alone, resulting in more than 12 wt% high-pure H2 (>99%) released below 250 °C. The synergetic effect of associating the dihydrogen reaction with mutually aided-metal cations on optimizing the dehydrogenation of this kind of composites may serve as an alternative strategy for developing and expanding the future B–N–H systems with superior and tuneable dehydrogenation properties.