Photoelectrochemical (PEC) characterizations were carried out by SP-200 Bio-Logic potentiostat in a three-electrode configuration under AM 1.5G illumination. the photoanode, Pt wire, and Ag/AgCl electrode were used as working, counter, and reference electrode, respectively. For the measurement of PEC performance, 0.5 M potassium phosphate (KPi) was used as the electrolyte under back-side (BiVO4) and front-side (Fe2O3) illumination, and epoxy resin (Loctite Epoxide-resin EA 9461 and EA 9466) was used to obtain certain surface area of the photoanodes (0.2 ~ 0.25 cm -2 ). Electrochemical impedance spectroscopy (EIS) was measured by SP-300 with 10 mV AC voltage amplitude and frequency range from 0.2 Hz to 1 MHz under the illumination of white light LED (SP-12-W5, cool white Luxeon Rebel). Numerical fitting of EIS data was conducted by Zview software.