Dissociation and Diffusion of Hydrogen on the Mg(0001) Surface: Catalytic Effect of V and Ni Double Substitution

To understand the effect of impurity concentration in hydrogen dissociation and diffusion, an extensive first-principles investigation has been performed over doubly substituted Mg surface and the findings have been compared to those of single substitution. The calculations have been carried out using density functional theory within the plane-wave pseudopotential approach employing projector-augmented wave potentials and generalized gradient approximation of Perdew-Burke-Ernzerhof exchange-correlation functional. Unlike single substitution, where the impurity atoms always prefer to replace one of the Mg atoms from the second layer, in the case of double substitution, when Ni and V atoms are doped simultaneously, the most stable configuration shows that Ni and V prefer to substitute Mg atoms from the first and second layers, respectively. The stabilization of Ni on the surface layer results in significant reduction in the dissociation barrier of the hydrogen molecule on the doped Mg surface.