title: Theoretical Verification of Photoelectrochemical Water Oxidation Using Nanocrystalline TiO2 Electrodes.
abstract: Mesoscopic anatase nanocrystalline TiO2 (nc-TiO2) electrodes play effective and efficient catalytic roles in photoelectrochemical (PEC) H2O oxidation under short circuit energy gap excitation conditions. Interfacial molecular orbital structures of (H2O)3 &amp;OH(TiO2)9H as a stationary model under neutral conditions and the radical-cation model of [(H2O)3&amp;OH(TiO2)9H]+ as a working nc-TiO2 model are simulated employing a cluster model OH(TiO2)9H (Yamashita/Jono's model) and a H2O cluster model of (H2O)3 to examine excellent H2O oxidation on nc-TiO2 electrodes in PEC cells. The stationary model, (H2O)3&amp;OH(TiO2)9H reveals that the model surface provides catalytic H2O binding sites through hydrogen bonding, van der Waals and Coulombic interactions. The working model, [(H2O)3&amp;OH(TiO2)9H]+ discloses to have a very narrow energy gap (0.3 eV) between HOMO and LUMO potentials, proving that PEC nc-TiO2 electrodes become conductive at photo-irradiated working conditions. DFT-simulation of stepwise oxidation of a hydroxide ion cluster model of OH-(H2O)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-TiO2 electrodes are now verified to become conductive by energy gap photo-excitation and the electrode surface provides powerful oxidizing sites for successive H2O oxidation to oxygen via hydrogen peroxide.
authors.affiliation: Frontier Research Institute, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan. yanagida@mls.eng.osaka-u.ac.jp.
authors.forename: Shozo
authors.initials: S
authors.lastname: Yanagida
authors.affiliation: Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1, Senbaru, Nishihara, Okinawa 903-0213, Japan. shou@sci.u-ryukyu.ac.jp.
authors.forename: Susumu
authors.initials: S
authors.lastname: Yanagisawa
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. yamasita@chemsys.t.u-tokyo.ac.jp.
authors.forename: Koichi
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. jono@tcl.t.u-tokyo.ac.jp.
authors.forename: Ryota
authors.initials: R
authors.lastname: Jono
authors.affiliation: Research Center for Advance Science and Technology, The university of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8904, Japan. csegawa@mail.ecc.u-tokyo.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Segawa
mesh_terms: D055664:Electrochemical Techniques; D004566:Electrodes; D004583:Electrons; D006860:Hydrogen Bonding; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; C009495:titanium dioxide; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D014025:Titanium
keywords: DFT; DSC; HOMO; Honda/Fujishima effect; LUMO; TiO2 photocatalysis; conductivity; spin density