Theoretical Verification of Photoelectrochemical Water Oxidation Using Nanocrystalline TiO(2) Electrodes

Mesoscopic anatase nanocrystalline TiO(2) (nc-TiO(2)) electrodes play effective and efficient catalytic roles in photoelectrochemical (PEC) H(2)O oxidation under short circuit energy gap excitation conditions. Interfacial molecular orbital structures of (H(2)O)(3) &OH(TiO(2))(9)H as a stationary model under neutral conditions and the radical-cation model of [(H(2)O)(3)&OH(TiO(2))(9)H](+) as a working nc-TiO(2) model are simulated employing a cluster model OH(TiO(2))(9)H (Yamashita/Jono’s model) and a H(2)O cluster model of (H(2)O)(3) to examine excellent H(2)O oxidation on nc-TiO(2) electrodes in PEC cells. The stationary model, (H(2)O)(3)&OH(TiO(2))(9)H reveals that the model surface provides catalytic H(2)O binding sites through hydrogen bonding, van der Waals and Coulombic interactions. The working model, [(H(2)O)(3)&OH(TiO(2))(9)H](+) discloses to have a very narrow energy gap (0.3 eV) between HOMO and LUMO potentials, proving that PEC nc-TiO(2) electrodes become conductive at photo-irradiated working conditions. DFT-simulation of stepwise oxidation of a hydroxide ion cluster model of OH(−)(H(2)O)(3), proves that successive two-electron oxidation leads to hydroxyl radical clusters, which should give hydrogen peroxide as a precursor of oxygen molecules. Under working bias conditions of PEC cells, nc-TiO(2) electrodes are now verified to become conductive by energy gap photo-excitation and the electrode surface provides powerful oxidizing sites for successive H(2)O oxidation to oxygen via hydrogen peroxide.