Decomposition mechanisms and the role of transition metal impurities in the kinetics of Ca(BH4)2·2NH3

Abstract We present first-principles density-function theory studies of the formation and migration of native point defects in Ca(BH4)2·2NH3, which is a promising material for hydrogen storage. According to analysis of the energetics, structures, formation and migration of hydrogen-, calcium-, boron- and nitrogen-related defects, we find that the diffusion of hydrogen interstitial ( H i − ) in the bulk is the rate-limiting step for decomposing Ca(BH4)2·2NH3. Our calculated results show that the activation energy for the decomposition process of Ca(BH4)2·2NH3 is 1.41 eV (in a closed vessel). Moreover, electrically active impurities such as Fe, Co and Ni can tailor the kinetics of dehydrogenation of Ca(BH4)2·2NH3 by shifting the Fermi level. These mechanisms provide an appropriate explaining for the experimentally observed improving of the kinetics for hydrogen desorption of Ca(BH4)2·2NH3 through doping transition metal chlorides in a closed vessel.