Reverse Electron Transfer from TiO2 to I2 in Nanocrystalline TiO2 Film Electrodes with Coadsorbed Bipyridine and Biquinoline Ruthenium Complexes

• Published in: Journal of physical chemistry. C 2007-01, Vol.111 (1), p.201-209
• Main Authors: Yanagida, Masatoshi, Miyamoto, Koji, Sayama, Kazuhiro, Kasuga, Kazuyuki, Kurashige, Mitsuhiko, Abe, Yoshimoto, Sugihara, Hideki
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp0606715

Reverse electron transfer from TiO2 to I2 in nanocrystalline TiO2 films with coadsorbed [NBu4]2[cis-Ru(Hdcbiq)2(NCS)2] (1; [NBu4]+ = tetrabutylammonium cation; H2dcbiq = 4,4‘-dicarboxy-2,2‘-biquinoline) and [NBu4]2[cis-Ru(Hdcbpy)2(NCS)2] (2; H2dcbpy = 4,4‘-dicarboxy-2,2‘-bipyridine) was investigated. The apparent electron lifetime decreased when 1 was coadsorbed with 2 on TiO2. The incident monochromatic photon-to-current conversion efficiency and the open-circuit photovoltage decreased substantially even when a small amount of 1 was coadsorbed with 2 on TiO2. The reduction of 1 on TiO2 was spectroelectrochemically observed at a potential that was more positive than the energy of the conduction band edge of the TiO2 films. These results suggest that the injected electron from photoexcited complex 2 reacted with I2 through 1. Reverse electron transfer from TiO2 to I2 depended not only on the electron density but also on the amount of 1 adsorbed on TiO2. Therefore, we assumed that the injected electron was trapped by 1 on TiO2 and then reacted with I2. If an injected electron diffused randomly in TiO2, the relative cross-section (σtrap) of electron trapping by 1 on TiO2 would be expected to be 1 and to be the same as that of trapping by 2. However, the σtrap value was much larger than expected, which indicates that the electron in TiO2 predominantly reacted with I2 through 1.