On the Theoretical and Experimental Control of Defect Chemistry, Electrical and Photoelectrochemical Properties of Hematite Nanostructures

摘要： Hematite (α-Fe2O3) is regarded as one of the most promising cost-effective and stable anode materials in photoelectrochemical applications, and its performance, like other transition metal oxides, depends strongly on its electrical and defect properties. In this work, the electrical and thermo-mechanical properties of undoped and Sn-doped α-Fe2O3 nanoscale powders were characterized in-situ under controlled temperatures (T = 250 to 400oC) and atmospheres (pO2 = 10-4 to 1 atm O2) to investigate their transport and defect properties. Frequency-dependent complex impedance spectra show that interfacial resistance between particles is negligible in comparison with particle resistance. Detailed defect models predicting the dependence of electron, hole, iron and oxygen vacancy concentrations on temperature and oxygen partial pressures for undoped and doped α-Fe2O3 were derived. Using these defect equilibria models, the operative defect regimes were established and the bandgap energy of undoped α-Fe2O3 and oxidation enthalpy of Sn-doped α-Fe2O3 were obtained from the analysis of the temperature and pO2 dependence of the electrical conductivity. Based on these results, we are able to explain the surprisingly weak impact of donor doping on the electrical conductivity of α-Fe2O3. Furthermore, experimental means based on the results of this study are given for successfully tuning hematite to enhance its photocatalytic activity for the water oxidation reaction.