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International Journal of Photoenergy
Volume 2013, Article ID 456583, 7 pages
http://dx.doi.org/10.1155/2013/456583
Research Article

Cosensitization Properties of Glutathione-Protected Au25 Cluster on Ruthenium Dye-Sensitized TiO2 Photoelectrode

1Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
2Research Institute for Science and Technology, Photocatalysis International Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
3Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
4Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1–3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
5Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan

Received 1 July 2013; Revised 6 October 2013; Accepted 8 October 2013

Academic Editor: Xie Quan

Copyright © 2013 Kazuya Nakata et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Cosensitization by glutathione-protected Au25 clusters on Ru complex, N719-sensitized TiO2 photoelectrodes is demonstrated. Glutathione-protected Au25 clusters showed no significant changes in properties after adsorption onto TiO2 particles, as confirmed by optical absorption spectroscopy, transmission electron microscopy, and laser desorption/ionization mass spectrometry. Adsorption property of the glutathione-protected Au25 clusters depends on the pH, which affects the incident photon-to-current conversion efficiency (IPCE) of the TiO2 photoelectrode containing Au25 clusters. When pH < 5, the IPCE increases with pH. Conversely, the IPCE decreases with pH when pH > 7. The IPCE of a TiO2 photoelectrode sensitized by both glutathione-protected Au25 clusters and N719 was increased compared with photoelectrodes containing either glutathione-protected Au25 clusters or N719, which suggests that glutathione-protected Au25 clusters act as a coadsorbent for N719 on TiO2 photoelectrodes. This is also supported by the results that the IPCE of N719-sensitized TiO2 photoelectrodes increased upon addition of glutathione. Furthermore, cosensitization by glutathione-protected Au25 clusters on N719-sensitized TiO2 photoelectrodes allows that wavelength of photoelectric conversion was extended to the near infrared (NIR) region. These results suggest that glutathione-protected Au25 clusters act not only as a coadsorbent to increase IPCE but also as an NIR-active sensitizer.