Density functional calculations were performed to study the H-atom diffusion on titanium dioxide (110) surface in the cases of water-molecule dissociation and splitting of the adjacent hydroxyl OH pair. It was shown that, when a water molecule was adsorbed at a surface O-vacancy site, a fragment H atom of the water molecule tends to diffuse toward the nearest-neighboring bridging-O sites by using a straight-line or relay-point path. As the result, a pair of surface hydroxyl OH was formed on the same O row. In a thermal process, on the other hand, such OH pair favourably splits only by using a relay-point path, i.e., by transferring one H atom from a bridging-O site to a next-neighboring one along the same O row by way of another in-plane O site. It was found that the latter splitting reaction was activated around room temperature.

First-Principles Calculations of Hydrogen Diffusion on Rutile TiO2(110) Surfaces. Kajita, S., Minato, T., Kato, H.S., Kawai, M., Nakayama, T.: Journal of Chemical Physics, 2007, 127[10], 104709