Overall water splitting using (oxy)nitride photocatalysts

Maeda, Kazuhiko; Teramura, Kentaro; Saito, Nobuo; Inoue, Yasunobu; Kobayashi, Hisayoshi; Domen, Kazunari

doi:10.1351/pac200678122267

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

http://dx.doi.org/10.1351/pac200678122267

Overall water splitting using (oxy)nitride photocatalysts

Kazuhiko Maeda¹, Kentaro Teramura¹, Nobuo Saito², Yasunobu Inoue², Hisayoshi Kobayashi³ and Kazunari Domen^1,4

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, (Ga_1-xZn_x)(N_1-xO_x), 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 (Ga_1-xZn_x)(N_1-xO_x) for overall water splitting is strongly dependent on both the cocatalyst and the crystallinity and composition of the material. The quantum efficiency of (Ga_1-xZn_x)(N_1-xO_x) 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.