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Pure Appl. Chem., 2006, Vol. 78, No. 12, pp. 2267-2276

Overall water splitting using (oxy)nitride photocatalysts

Kazuhiko Maeda1, Kentaro Teramura1, Nobuo Saito2, Yasunobu Inoue2, Hisayoshi Kobayashi3 and Kazunari Domen1,4

1 Department of Chemical System Engineering, The University of Tokyo,7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
2 Department of Chemistry, Nagaoka University of Technology, Nagaoka 940-2188, Japan
3 Department of Chemistry and Materials Technology, Faculty of Engineering and Design,Kyoto Institute of Technology, Goshokaido-cho, Matsugasaki, Sakyo-ku,Kyoto 606-8585, Japan
4 Solution Oriented Research for Science and Technology (SORST) programs of the Japan Science and Technology Agency (JST),4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012, Japan

Abstract: Oxynitride photocatalysts with d10 electronic configuration are presented as effective non-oxide catalysts for overall water splitting. Germanium nitride (β-Ge3N4) having a band gap of 3.8-3.9 eV modified with RuO2 nanoparticles as a cocatalyst is shown to achieve stoichiometric decomposition of H2O into H2 and O2 under UV irradiation (λ > 200 nm). A novel solid solution of GaN and ZnO, (Ga1-xZnx)(N1-xOx), with a band gap of 2.4-2.8 eV (depending on composition) achieves overall water splitting under visible light (λ > 400 nm) when loaded with an appropriate cocatalyst. The narrower band gap of the solid solution is attributed to the bonding between Zn and N atoms at the top of the valence band. The photocatalytic activity of (Ga1-xZnx)(N1-xOx) for overall water splitting is strongly dependent on both the cocatalyst and the crystallinity and composition of the material. The quantum efficiency of (Ga1-xZnx)(N1-xOx) with Rh and Cr mixed-oxide nanoparticles is 2-3 % at 420-440 nm, which is the highest reported efficiency for overall water splitting in the visible-light region.