Interplay between Water and TiO2 Anatase (101) Surface with Subsurface Oxygen Vacancy

The interaction between water and the TiO2 anatase (101) surface with a subsurface V-O is studied using first-principles calculations. Upon water adsorption, the relative stability of the subsurface and surface V-O reverses. The surface V-O becomes energetically more stable than its subsurface counterpart, which induces V-O to migrate from the subsurface to the surface with a very low energy barrier. Then the adsorbed water molecule can easily dissociate through a barrierless pathway facilitated by surface V-O. This reaction pathway has a similar energy barrier with another pathway under which water dissociates with the presence of subsurface V-O followed by V-O migration from the subsurface layer to the surface layer, indicating that subsurface V-O can facilitate water dissociation directly, or, via surface V-O indirectly. This novel interplay between the adsorbate and substrate defects may provide a new way to explain the origin of the activity of anatase (101) in photocatalysis in aqueous surroundings.