Department of Materials Science and Engineering, Tokyo Institute of Technology^* Department of Materials Science and Engineering, Tokyo Institute of Technology, Japan^** Department of Chemical System Engineering, The University of Tokyo, Japan^***
○Yong Phat^* Masatomo Yashima^** Kazuhiko Maeda^*** Kentaro Teramura^*** Tsuyoshi Takada^*** Kazunari Domen^***

ABCmyOverall water-splitting using a photocatalyst is an attractive solution for the supply of clean and recyclable hydrogen energy. Although a number of photocatalysts have been proposed, most function only in the ultraviolet region (e.g., TiO₂). While photocatalysts such as doped TiO₂, Ta₃N₅, TaON and LaTiO₂N function under visible light, these materials are not able to achieve overall water splitting. Recently, Maeda et al. [1] reported the solid solution of GaN and ZnO ((Ga_1－-xZn_x)(N_1－-xO_x)) as a new type of oxynitride photocatalyst that is capable of overall water splitting under visible light. Here we report the crystal structure and optical properties of (Ga_0.87Zn_0.13)(N_0.83O_0.16) [2]. This material was demonstrated to absorb visible light at wavelengths of up to ca. 500 nm, and to exhibit photoluminescence at around 650 nm (1.9 eV) even at room temperature. The Rietveld analyses of neutron powder diffraction data of the (Ga_0.87Zn_0.13)(N_0.83O_0.16) (P6₃mc) confirmed that the oxygen substitutes for nitrogen in the crystal structure, and may be responsible for the desirable optical properties of (Ga_0.87Zn_0.13)(N_0.83O_0.16) as a photocatalyst for visible light-driven overall water splitting. The nuclear density mapping revealed the structure to be free of interstitial sites and large disorder.
[1] K. Maeda et al., J. Am. Chem. Soc. 127 (2005) 8286.
[2] M. Yashima et al., Chem. Phys. Lett., 416 (2005) 225.