Ammine bimetallic (Na, Zn) borohydride for advanced chemical hydrogen storage

Abstract

The synthesis and dehydrogenation performance of purified NaZn(BH₄)₃ with a new phase and its novel ammine metal borohydride, NaZn(BH₄)₃·2NH₃, were first reported. Structure analysis shows that NaZn(BH₄)₃·2NH₃ crystallizes in an orthorhombic structure with lattice parameters of a = 7.2965(2) Å, b = 10.1444(2) Å and c = 12.9714(3) Å and space group P2₁nb, in which the Zn atoms are located in a tetrahedral coordination environment with two NH₃ molecules and two BH₄⁻ units, presenting a novel 3D framework comprised of isolated BH₄⁻¹ units and [NaZn(BH₄)₂(NH₃)₂]⁺ complexes. Dehydrogenation results showed that the ZnCl₂ assisted NaZn(BH₄)₃·2NH₃ is able to release 7.9 wt% hydrogen at 110 °C without the concomitant release of undesirable gases such as ammonia and/or boranes, thereby demonstrating the potential of the ammoniated Zn-based borohydrides to be used as solid hydrogen storage materials.