Theoretical study of hydrogen adsorption kinetics: Mg17Al12 vs pure Mg

The adsorption and dissociation of hydrogen molecules on Mg17Al12(100), Mg17Al12(110), Mg17Al12(111) and Mg(0001) surfaces are investigated by the first-principles calculations. We find that the H adsorption on Mg17Al12 systems are all stronger than that of Mg(0001). Among them, the lowest adsorption energies of H atoms are obtained in the Mg17Al12(110) system, which is −0.278 and −0.247 eV/H when the H coverage is 1/11 and 2/11 ML, respectively. Furthermore, the Mg17Al12(110) surface presents an energy path of hydrogen dissociation with a minimum barrier of 0.59 eV, which is smaller than that of Mg(0001) surface (0.84 eV). The electronic structure analysis illustrates that the bonding between H atoms and Mg17Al12(110) surface is enhanced, although H atoms obtain similar charges on the Mg17Al12(110) and Mg(0001) surfaces. Moreover, the lowered dissociation barrier on the three studied Mg17Al12 surfaces, are likely ascribed to the stronger hybridization of H 1s and Al 3s orbitals, leading to the accelerated hydrogen adsorption kinetics on Mg17Al12 surface with respect to the pure Mg surface.