It was noted that it was well known, both theoretically and experimentally, that alloying MgH2 with transition elements could significantly improve the thermodynamic and kinetic properties for H2 desorption, as well as the H2 intake by bulk Mg. Here, a density functional theory investigation was made of hydrogen dissociation and surface diffusion over a Ni-doped surface, and the results were compared with previously investigated Ti-doped Mg(00•1) and pure Mg(00•1) surfaces. The results showed that the energy barrier for H dissociation on the pure Mg(00•1) surface was high, while it was small or zero when Ni or Ti was added to the surface as a dopant. It was found that the binding energy of the two H atoms near to the dissociation site was high on Ti; effectively impeding diffusion away from the Ti site. By contrast, it was found that, on Ni, the energy barrier to diffusion was much reduced. Therefore, although both Ti and Ni promoted H2 dissociation, only Ni appeared to be a good catalyst for Mg hydrogenation, allowing diffusion away from the catalytic sites. Experimental results corroborated these theoretical one, i.e., faster hydrogenation of the Ni-doped Mg sample as compared with the reference Mg- or Ti-doped Mg.

Hydrogen Dissociation and Diffusion on Ni- and Ti-Doped Mg(0001) Surfaces. M.Pozzo, D.Alfè, A.Amieiro, S.French, A.Pratt: Journal of Chemical Physics, 2008, 128[9], 094703