Visible-Light-Induced Water Splitting Based on Two-Step Photoexcitation between Dye-Sensitized Layered Niobate and Tungsten Oxide Photocatalysts in the Presence of a Triiodide/Iodide Shuttle Redox Med

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• 作者：Ryu Abe ; Kenichi Shinmei ; Nagatoshi Koumura ; Kohjiro Hara ; Bunsho Ohtani
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：November 13, 2013
• 年：2013
• 卷：135
• 期：45
• 页码：16872-16884
• 全文大小：865K
• 年卷期：v.135,no.45(November 13, 2013)
• ISSN：1520-5126

文摘

Water splitting into H₂ and O₂ under visible light was achieved using simple organic dyes such as coumarin and carbazole as photosensitizers on an n-type semiconductor for H₂ evolution, a tungsten(VI) oxide (WO₃) photocatalyst for O₂ evolution, and a triiodide/iodide (I₃^{鈥?/sup>/I鈥?/sup>) redox couple as a shuttle electron mediator between them. The results on electrochemical measurements revealed that the oxidized states of the dye molecules having an oligothiophene moiety (two or more thiophene rings) in their structures are relatively stable even in water and possess sufficiently long lifetimes to exhibit reversible oxidation鈥搑eduction cycles, while the carbazole system required more thiophene rings than the coumarin one to be substantially stabilized. The long lifetimes of the oxidized states enabled these dye molecules to be regenerated to the original states by accepting an electron from the I鈥?/sup> electron donor even in an aqueous solution, achieving sustained H₂ and I₃鈥?/sup> production from an aqueous KI solution under visible light irradiation when they were combined with an appropriate n-type semiconductor, ion-exchangeable layered niobate H₄Nb₆O₁₇. The use of H₄Nb₆O₁₇ loaded with Pt cocatalyst inside the interlayer allowed the water reduction to proceed preferentially with a steady rate even in the presence of a considerable amount of I₃鈥?/sup> in the solution, due to the inhibited access of I₃鈥?/sup> to the reduction site, Pt particles inside, by the electrostatic repulsion between the I₃鈥?/sup> anions and the negatively charged (Nb₆O₁₇)4鈥?/sup> layers. It was also revealed that the WO₃ particles coloaded with Pt and IrO₂ catalysts exhibited higher rates of O₂ evolution than the WO₃ particles loaded only with Pt in aqueous solutions containing a considerable amount of I鈥?/sup>, which competitively consumes the holes and lowers the rate of O₂ evolution on WO₃ photocatalysts. The enhanced O₂ evolution is certainly due to the improved selectivity of holes toward water oxidation on IrO₂ cocatalyst, instead of undesirable oxidation of I鈥?/sup>. Simultaneous evolution of H₂ and O₂ under visible light was then achieved by combining the Pt/H₄Nb₆O₁₇ semiconductor sensitized with the dye molecules having an oligothiophene moiety, which can stably generate H₂ and I₃鈥?/sup> from an aqueous KI solution, with the IrO₂鈥揚t-loaded WO₃ photocatalyst that can reduce the I₃鈥?/sup> back to I鈥?/sup> and oxidize water to O₂.}