It was noted that the kinetics of hydrogen absorption by bulk Mg was affected by two main activated processes: the dissociation of the H2 molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed needed to have a low barrier. Here, a systematic ab initio density functional theory investigation was made of H2 dissociation and subsequent atomic H diffusion on Ti-, V-, Zr-, Fe-, Ru-, Co-, Rh-, Ni-, Pd-, Cu- or Ag-doped Mg(00•1) surfaces. The calculations showed that doping the surface with transition metals on the left of the periodic table eliminated the barrier to the dissociation of the molecule, but the H atoms bonded very strongly to the transition metal, thereby hindering diffusion. Conversely, transition metals on the right of the periodic table did not bind H. However, they did not significantly reduce the barrier to H2 dissociation. The results showed that Fe, Ni and Rh and, to some extent, Co and Pd, were all exceptions, combining low activation barriers for both processes; with Ni being the best possible choice.

Hydrogen Dissociation and Diffusion on Transition Metal (= Ti, Zr, V, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-Doped Mg(0001) Surfaces. M.Pozzo, D.Alfè: International Journal of Hydrogen Energy, 2009, 34[4], 1922-30