Adsorption and dissociation of H₂ on Al₄Si_m (m = 2, 3, and 4) clusters

Abstract

Hydrogen in alanates forms AlH4− unit and the bonding strength depends on the electron donor property of the metal atoms. The electronic structures of Al─Si clusters are similar to metal clusters but the Al atom is a weaker electron donor than that in light metal alanates, so hydrogen may form weaker Al─H bonds in Al─Si systems. This article studies the adsorption and dissociation of H2 on Al4Si m (m = 2, 3, and 4) clusters by using density functional theory. The physisorption of H2 molecules on Al4Si m is very weak, the average binding energies of two H atoms on Al4Si m fall in the range –0.61 to –1.50 eV. It suggests that Al─Si hydrides can be candidates for hydrogen storage at ambient conditions. The investigation on the H2 dissociation processes shows that the lowest energy barrier is 0.76 eV, which implies that H2 dissociation can occur at moderate temperatures.