期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 120, 期 6, 页码 3250-3258出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.5b08013
关键词
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资金
- Swiss National Science Foundation [132126, 137868, 121306, 20NA21-145936]
- Strategic Korean-Swiss Cooperative Program in Science and Technology within project Spectroscopy on photoelectrochemical electrode materials: SOPEM [NRF-2013K1A3A1A14055158]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
The origin, the nature, and the electronic structure of surface defects causing surface states on metal oxides and their role in solar water splitting have been under scrutiny for several decades. In the present study, the surface of hematite films is treated with an oxygen plasma and then subject to a detailed investigation with electroanalytical methods and element orbital specific X-ray spectroscopy. We observe a systemic variation of photoelectrochemical properties with oxygen treatment time. Fe 2p and O is core level X-ray photoelectron spectra and resonant valence band photoemission at the Fe 3p edge reveal the filling of prevalent oxygen vacancies with concomitant oxidation of Fe2+ to Fe3+ upon the oxygen treatment. The dc bias dependent impedance spectra confirm how a prevalent capacitive surface state, which evolves parallel with the photocurrent onset potential, becomes diminished upon oxygen treatment. Surface states of iron induce higher reactivity toward water oxidation than oxygen surface states. correlation between oxygen vacancy filling, concentration of surface states, and photocurrent density in the course of treatment confirms that the surface defects are of a capacitive nature and that the onset of water splitting can be considered as a result of dielectric breakdown in an interfacial hydroxide layer between photoanode and water.
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