Theoretical study of hydrogen dissociation and diffusion on Nb and Ni co-doped Mg(0001): A synergistic effect

The interaction of H-2 with clean, Ni and Nb doped Mg(0001) surface are investigated by first-principles calculations. Individual Ni and Nb atoms within the outermost surface can reduce the dissociation barrier of the hydrogen molecule. They, however, prefers to substitute for the Mg atoms within the second layer, leading to a weaker catalytic effect for the dissociation of H-2, a bottleneck for the hydriding of MgH2. Interestingly, co-doping of Ni and Nb stabilizes Ni at the first layer, and results in a significant reduction of the dissociation barrier of H-2 on the Mg surface, coupled with an increase of the diffusion barrier of H. Although codoped Ni and Nb shows no remarkable advantage over single Nb here, it implies that the catalytic effect could be optimized by co-doping of modest transition metals with balanced barriers for dissociation of H-2 and diffusion of H on Mg surfaces. (C) 2012 Elsevier B.V. All rights reserved.