New aspects of heterogeneous photocatalysts for water decomposition
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JOURNAL REVIEW
New Aspects of Heterogeneous Photocatalysts for Water Decomposition Kazunari Domen *, Michikazu Hara, Junko N. Kondo, Tsuyoshi Takata, Akihiko Kudo*, Hisayoshi Kobayashi** and $:asunobu Inoue* ** Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan *Department of Applied Chemistry, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjyuku-ku~ Tokyo 162-8601, Japan **Department of Chemical Technology, College of Science and Industrial Technology, Kurashiki University of Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki-shi, Okayama 712-8505, Japan ***Department of Chemistry, Nagaoka University of Technology, Nagaoka 940-2188, Japan
(Received 24 September 2001 9 accepted 30 September 200I)
Abs~ract-Sev~-al new photocatalysts for ovel-all water splitting are described. Under UV light in-adiation (270 nm), La-doped Na~PaOemodified with NiO decomposed water into H3 and 03 with extremely high quantuln effide~lcy. Under an optimized conditiol~ the apparent quantum efficiency, which was estimated with numbers of irpadiated photons and evolved H, molecules, reached 56%. New stable photocatalytic materials containing elements with d '~ electronic configuration sudl as In>, Sn4+and Sb~+were developed for overall water splitting. Some mesoporous oMdes were proved to be effective photocatalysts. (Oxy)nitrides of some early transition metals, i.e., Ta, Nb and Ti, were found to be stable materials having potentials for H3 and O~ evolutions under visible light irradiation (,,,, ~
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a~ ~~ i~q~" ,~'420 nm) in an aqueous silver nitrate is shown in Fig. 10. The pH of the initial solution was controlled at about 8 by adding La,O3 powder. Under this condition, O, evolved rapidly in the beginning of the reaction and the rate decreased gradually with the consumption of Ag+ cations and the decrease of the pH. The initial aplmrent quan_n.rn elK o r e a n J. Chemu E n g , ( V o [ 18, N o . 6)
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ficiency of the Q, evolution was ca. 1(~o. Again N2 evolution was negligible. From the result it is concluded that the valence lmnd of TaON has enough potential to o~dize water into Q,. It is also suggested that this o?gnilride, TaON, is a stable material during water decompositk~ Other (ox-y)nitrides such as Ta~N:, LaTiO,N showed similar behaviors for H2 and O2 evolution reactions, which indicates these materials also have the potential for overall water splitting. As mentioned above, at present O~ evolution efficiency (ca. 10~ is high enough while H, evolution efficienc
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