Pivotal Role and Regulation of Proton Transfer in Water Oxidation on Hematite Photoanodes
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- 作者：Yuchao Zhang ; Hongna Zhang ; Hongwei Ji ; Wanhong Ma ; Chuncheng Chen ; Jincai Zhao
- 刊名：Journal of the American Chemical Society
- 出版年：2016
- 出版时间：March 2, 2016
- 年：2016
- 卷：138
- 期：8
- 页码：2705-2711
- 全文大小：355K
- ISSN：1520-5126
文摘
Hematite is a promising material for solar water splitting; however, high efficiency remains elusive because of the kinetic limitations of interfacial charge transfer. Here, we demonstrate the pivotal role of proton transfer in water oxidation on hematite photoanodes using photoelectrochemical (PEC) characterization, the H/D kinetic isotope effect (KIE), and electrochemical impedance spectroscopy (EIS). We observed a concerted proton–electron transfer (CPET) characteristic for the rate-determining interfacial hole transfer, where electron transfer (ET) from molecular water to a surface-trapped hole was accompanied by proton transfer (PT) to a solvent water molecule, demonstrating a substantial KIE (∼3.5). The temperature dependency of KIE revealed a highly flexible proton transfer channel along the hydrogen bond at the hematite/electrolyte interface. A mechanistic transition in the rate-determining step from CPET to ET occurred after OH– became the dominant hole acceptor. We further modified the proton–electron transfer sequence with appropriate proton acceptors (buffer bases) and achieved a greater than 4-fold increase in the PEC water oxidation efficiency on a hematite photoanode.