Catalytic Properties of Near-Surface Alloy of Transition Metal in Aluminum: A Density Functional Theory Study of Structural and Electronic Properties

摘要

On the basis of detailed studies of structural and electronic properties with first-principles calculations, we have carefully analyzed enhanced H2 splitting catalyzed by the early transition metals that substitutionally doped in the top layer and the subsurface of an ideal flat Al surface and that at the edge site of a stepped surface. The 3d orbitals facilitating Kubas . interaction significantly reduce the activation energy of H2 splitting catalyzed by a transition metal doped in the top surface. The catalyst doped in the subsurface could not develop Kubas interaction with H3 because of the screening from the charge distributed on the top surface, whose role could be understood by combining the structural deformation induced by the doping, the attraction of the dopant to the electrons distributed around Al atoms in the top layer, and the d orbital attendance in the reaction. For the sake of recycling perspectives of the doped catalyst, the diffusion of the dissociated H atoms has also been studied. Thus, the Sc and Ti doping at the lower edge site of the stepped surface are better for their low activation energies. The atomic size and electronegativity could be used to aid new catalyst design for enhancing the hydrogen recharge properties of metal alanate hydrides. Accordingly, the near-surface alloying of Sc, Ti, Zr, Nb, Hf, and Ta in the aluminum surface could be expected to have superior catalytic properties.