Photoelectrochemical (PEC) water splitting to generate hydrogen fuel is a promising route to solve energy and environmental issues. Good electron conductivity is crucial of photoanode for high charge separation efficiency. It is found that oxygen vacancy plays an important role in conductivity improvement of oxide semiconductors as photoanode for water splitting, such as TiO2, WO3, and Fe2O3. However, oxygen vacancy may also affect the light absorption and the charge transfer through the solid / electrolyte interface. The roles of oxygen vacancy have not been thoroughly discussed in the past. Herein, using hematite as an example, the effects of oxygen vacancy on bulk charge transport and surface catalysis are quantitatively analyzed by decoupling photon absorption, interfacial charge transfer and charge separation processes. Oxygen vacancy improves the charge separation of both pristine and Ti-doped hematite. However, opposite observations are found in charge transfer process for pristine and Ti-doped hematite, positive effect in pristine hematite but negative effect in Ti-doped one. Electrochemical technique is used to analyze the different influences on pristine and Ti-doped hematite to unravel the mechanism of the opposite observations on charge transfer caused by oxygen vacancy. In this study, two active surface species (denoted as S1, S2) were found to participate the water oxidation process. S1 is closely related to oxygen vacancy while S2 arises from Ti doping. Oxygen vacancy can promote the formation of species S1 on the surface, which results in higher charge transfer efficiency in pristine hematite after nitrogen treatment. Ti doping can generate both S1 and S2 surface species. However, oxygen vacancy has some negative effect on S2 species, which leads to a lower charge transfer efficiency of Ti-doped hematite with oxygen vacancy compared the one without oxygen vacancy. The current study sheds lights on how oxygen vacancy affects various aspects of important factors behind PEC performance, which is helpful to the development of more efficient photoanodes in the future.

New insight into the roles of oxygen vacancy in hematite for solar water splitting

254th National Meeting (2017)

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