Introduction of oxygen vacancies into hematite in local reducing atmosphere for solar water oxidation

摘要： Sn Doping and creation of oxygen vacancies have been adopted universally to overcome the poor electric conductivity and unfavorable hole diffusion length of α-Fe2O3 photoanodes. Generally, Sn doping is realized via longitudinal migration of tin element from FTO (fluorine-doped tin oxide) substrates into α-Fe2O3 at high temperature. To introduce oxygen vacancies along with Sn into hematite for further promoting its electric conductivity, we have created a local reducing atmosphere via partial oxidation of graphite while doping hematite with Sn. The donor density of the resultant Fe2O3 photoanode annealed on graphite (G-Fe2O3) at 770 °C for 20 min is increased to ～1.7 times that of the counterpart annealed on SiO2 powders (S-Fe2O3), indicating that the electric conductivity of hematite is improved after introduction of oxygen vacancies. Moreover, oxygen vacancies have been demonstrated to significantly reduce the charge transfer resistance of Sn doped hematite. Consequently, the photocurrent density of G-Fe2O3 is enhanced remarkably (～70%) compared with S-Fe2O3. However, the improvement in photocurrent density due to oxygen vacancies becomes less significant when more Sn is doped into hematite. The strategy for creation of oxygen vacancies reported here can be extended to other photoanodes for better understanding the effect of oxygen vacancies on PEC performance.