摘要 : Complex metal hydride is a promising hydrogen storage material for automobile applications due to its reversible storage capacity. The presence of transition metal halide is found to improve significantly the kinetics of H_2 adsor... 展开 Complex metal hydride is a promising hydrogen storage material for automobile applications due to its reversible storage capacity. The presence of transition metal halide is found to improve significantly the kinetics of H_2 adsorption and desorption processes. Experimental studies have indicated the formation of distorted MAl_3 phase where M = Sc, Ti, Zr. In this study, a first-principles density functional study has been performed to investigate the hydrogen interaction and saturation on stable tetrahedral MAl_3 clusters [M = Li, Sc, Ti, and Zr] by employing spin-polarized hybrid and non-local density functionals. On saturation, the first H_2 molecule undergoes chemisorption in the transition metals while further loading results in physisorption with the Kubas-type H2 interaction. Activation energy barrier for the H_2 dissociation over the cluster is calculated to be ~0.2 eV for the transition metals. Effect of external electric field on the MAl_3H_4 cluster with molecular H_2 is studied which leads to polarization of physisorbed H_2 and the cluster. The results offer an explanation for catalysts role in improving the kinetics of H_2 sorption process in complex metal hydrides. 收起