A first-principles study of hydrogen interaction and saturation on ScAl3

Abstract Complex metal hydrides are promising hydrogen storage material for mobile applications. The presence of scandium catalysts in complex metal hydrides is found to improve significantly the kinetics of H 2 adsorption and desorption. The exact role of these additives is not completely understood. NMR studies suggests the presence of distorted ScAl 3 phase which is attributed to the enhancement of reversible uptake and release rates of H 2 . In this study, we have investigated the hydrogen interaction and saturation on stable ScAl 3 cluster at various sites using the density functional theory by employing unrestricted B3LYP/6-311++G(d,p) and the GGA-PW91/DNP methods. From natural bond orbital charge analysis and electrostatic potential superimposed on electron density plots, ScAl 3 is found to be more polarized and Sc atom in ScAl 3 cluster has higher negative charge and electron density over Al atoms. H 2 undergoes dissociative chemisorption on the Sc atop site in ScAl 3 resulting in Sc–H–Al bridge structure. The hydrogen saturation is studied by sequential H 2 adsorption on ScAl 3 cluster. In the Sc site, the first H 2 molecule undergoes dissociative chemisorption and further addition results in H 2 physisorption with the maximum loading of 6 H 2 molecules resulting in stable ScAl 3 H 12 structure. To obtain mechanistic insights into the hydrogenation process, the transition state and activation energy of H 2 dissociation on the ScAl 3 system has been determined.