Decomposition Mechanism of Zinc Ammine Borohydride: A First-Principles Calculation

The decomposition mechanism of zinc ammine borohydride ([Zn(NH3)2][BH4]2) has been studied by density functional theory calculation. The release of B2H6 and BH3 is predicted to be kinetically and/or thermodynamically unfavorable for [Zn(NH3)2][BH4]2, in agreement with experimental results that no boranes were detected during decomposition. The climbing image nudged elastic band calculation and ab initio molecular dynamics simulations indicate the formation of NH3BH3 and B2H7– intermediates during decomposition of [Zn(NH3)2][BH4]2, which is different from that observed for other reported ammine metal borohydrides. The dehydrogenation occurs through reaction pathways involving transfer of hydrides from the Zn cation to BH4– or transfer of protons from NH3BH3 to NH3.