Activation Energies for the Rate-Limiting Step in Water Photooxidation by Nanostructured 伪-Fe2O3 and TiO2

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• 作者：Alexander J. Cowan ; Christopher J. Barnett ; Stephanie R. Pendlebury ; Monica Barroso ; Kevin Sivula ; Michael Gr盲tzel ; James R. Durrant ; David R. Klug
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：July 6, 2011
• 年：2011
• 卷：133
• 期：26
• 页码：10134-10140
• 全文大小：879K
• 年卷期：v.133,no.26(July 6, 2011)
• ISSN：1520-5126

文摘

Competition between charge recombination and the forward reactions required for water splitting limits the efficiency of metal-oxide photocatalysts. A key requirement for the photochemical oxidation of water on both nanostructured 伪-Fe₂O₃ and TiO₂ is the generation of photoholes with lifetimes on the order of milliseconds to seconds. Here we use transient absorption spectroscopy to directly probe the long-lived holes on both nc-TiO₂ and 伪-Fe₂O₃ in complete PEC cells, and we investigate the factors controlling this slow hole decay, which can be described as the rate-limiting step in water oxidation. In both cases this rate-limiting step is tentatively assigned to the hole transfer from the metal oxide to a surface-bound water species. We demonstrate that one reason for the slow hole transfer on 伪-Fe₂O₃ is the presence of a significant thermal barrier, the magnitude of which is found to be independent of the applied bias at the potentials examined. This is in contrast to nanocrystalline nc-TiO₂, where no distinct thermal barrier to hole transfer is observed.