Molecular Mechanism of Water Oxidation Reaction at Photo-Irradiated TiO₂ and Related Metal Oxide Surfaces

Recent studies on the molecular mechanism of water photooxidation (or oxygen photoevolution) reaction on TiO2 and related metal oxides or oxynitrides are reviewed. It is shown that a lot of experimental and theoretical studies give definite support to our recently proposed new mechanism, called “nucleophilic attack of H2O” or “Lewis acid-base” mechanism. The new mechanism has the prominent features that it possesses energetic and kinetics different from the conventional electron-transfer mechanism and can explain water photooxidation reaction on visible-light responsive metal oxides or oxynitrides, contrary to the conventional one. The result indicates that the new mechanism is useful for searching for new efficient visible-light responsive materials for solar water splitting.