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Open AccessArticle

Theoretical Verification of Photoelectrochemical Water Oxidation Using Nanocrystalline TiO2 Electrodes

Frontier Research Institute, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1, Senbaru, Nishihara, Okinawa 903-0213, Japan
Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Research Center for Advance Science and Technology, The university of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8904, Japan
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
The authors contributed equally to this work.
Academic Editor: Pierre Pichat
Molecules 2015, 20(6), 9732-9744;
Received: 31 December 2014 / Accepted: 12 May 2015 / Published: 27 May 2015
(This article belongs to the Special Issue Photocatalysis)
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 &OH(TiO2)9H as a stationary model under neutral conditions and the radical-cation model of [(H2O)3&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&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&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. View Full-Text
Keywords: DFT; HOMO; LUMO; spin density; conductivity; TiO2 photocatalysis; DSC; Honda/Fujishima effect DFT; HOMO; LUMO; spin density; conductivity; TiO2 photocatalysis; DSC; Honda/Fujishima effect
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Yanagida, S.; Yanagisawa, S.; Yamashita, K.; Jono, R.; Segawa, H. Theoretical Verification of Photoelectrochemical Water Oxidation Using Nanocrystalline TiO2 Electrodes. Molecules 2015, 20, 9732-9744.

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