Effects of doping on photocatalytic activity for water splitting of metal oxides and nitride

Naoki Arai; Nobuo Saito; Hiroshi Nishiyama; Haruhiko Kadowaki; Hisayoshi Kobayashi; Kazunori Sato; Yasunobu Inoue

doi:10.1117/12.730826

11 September 2007 Effects of doping on photocatalytic activity for water splitting of metal oxides and nitride

Naoki Arai, Nobuo Saito, Hiroshi Nishiyama, Haruhiko Kadowaki, Hisayoshi Kobayashi, Kazunori Sato, Yasunobu Inoue

Proceedings Volume 6650, Solar Hydrogen and Nanotechnology II; 665008 (2007) https://doi.org/10.1117/12.730826
Event: Solar Energy + Applications, 2007, San Diego, California, United States

Abstract

The effects of metal-ion doping or replacement on the photocatalytic performance for water splitting of d¹⁰ and d⁰ metal oxides and d¹⁰ metal nitride were studied. The photocatalysts examined were (1) α-Ga_2-2xIn_2xO₃ and ZnGa_2-2xIn_2xO₄ in which In³⁺ was added to Ga₂O₃ and ZnGa₂O₄, respectively, (2) Y_xIn_2-xO₃ being a solid solution of In₂O₃ and Y₂O₃, (3) metal ion doped CeO₂, and (4) metal ion doped GaN. The photocatalytic activity of 1 wt % RuO₂-loaded α-Ga_2-2xIn_2xO₃ increased sharply with increasing x, reached a maximum at around x=0.02, and considerably decreased with further increase in x. The DFT calculation showed that the band structures of α-Ga_2-2xIn_2xO₃ had the contribution of In 4d orbital to the valence band and of In5s orbital to the conduction band. Similar effects were observed for ZnGa_2-2xIn_2xO₄. RuO₂-dispersed Y_xIn_2-xO₃ had a capability of producing H₂ and O₂ in the range x=1.0-1.5 in which the highest activity was obtained at x=1.3. The structures of both InO₆ and YO₆ octahedra were deformed in the solid solution,, and the hybridization of In5s5p and Y4d orbitals in the conduction band was enhanced. Undoped CeO₂ was photocatalytically inactive, but metal ion-doped CeO₂ showed a considerable photocatalytic activity. The activation occurred in the case that metal ions doped had larger ion sizes than that of Ce⁴⁺. The small amount doping of divalent metal ions (Zn²⁺ and Mg²⁺) converted photocatalytically inactive GaN to an efficient photocatalyst. The doping was shown to produce p-type GaN which had the large concentration and high mobility of holes. The roles of metal ion doping and replacement in the photocatalytic properties are discussed.

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Naoki Arai, Nobuo Saito, Hiroshi Nishiyama, Haruhiko Kadowaki, Hisayoshi Kobayashi, Kazunori Sato, and Yasunobu Inoue "Effects of doping on photocatalytic activity for water splitting of metal oxides and nitride", Proc. SPIE 6650, Solar Hydrogen and Nanotechnology II, 665008 (11 September 2007); https://doi.org/10.1117/12.730826

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