TiO₂ surface active sites for water splitting

The mechanism of photoreactivity between the TiO₂ surface and H₂O, and the related charge transfer, is considered in terms of both collective and local properties. It is shown that the effective charge transfer between TiO₂ and water requires the presence of surface active sites that are able to provide electron holes to adsorbed water molecules. Titanium vacancies located at or near the surface are identified as the active sites for water adsorption leading to the formation of an active complex and resulting, in consequence, in water splitting. A model of the photoreactivity between the TiO₂ surface and water is proposed. This model indicates that the photoreactivity of the TiO₂-based photoelectrode may be enhanced through imposition of the surface active sites (Ti vacancies) in a controlled manner by surface engineering.