Dehydrogenation mechanisms of Ca(NH2BH3)2: The less the charge transfer, the lower the barrier

Our first-principles study of Ca(NH2BH3)2 reveals that the gas phase energy barrier for the first H2 release is 1.90 eV via a Ca⋯H transition state and 1.71 eV via an N–H⋯B transition state for the second H2 release. In the dimer, the barrier for H2 release from the bridging [NH2BH3]− species is 1.60 eV via an N–H⋯B transition state, and 0.94 eV via an N–H⋯B transition state for the non-bridging [NH2BH3]− species. Analysis of the atomic charge distribution shows that the mechanism of dehydrogenation is determined by the charge transfer between the transition state and the initial state: the less the charge transfer, the lower the barrier to dehydrogenation.