Bias‐Free Photoelectrochemical Water Oxidation Coupled with Electrochemical Oxygen Reduction Reaction via Fe‐Based Electrodes with Long‐Term Operation

Abstract Photoelectrochemistry (PEC) is a green and sustainable approach in the synthesis of H₂O₂, depending on the semiconductor to initiate two‐electron water oxidation into hydrogen peroxide (H₂O₂). However, the photoanodes generally have sluggish charge transfer and a limited number of active sites, which limit the yield and faradaic efficiency (FE) for the production of H₂O₂. Herein, Ti‐doped Fe₂O₃ photoanode with the modification of ZnO passivation layer (ZnO/Ti‐Fe₂O₃) for PEC H₂O₂ production is developed. The optimized photoanode has shown a high FE and selectivity for two‐electron water oxidation, achieving a yield approaching 0.56 µmol min⁻¹ cm⁻² at 1.23 V_RHE and an average FE over 80% in the potential range from 1.0 to 1.6 V_RHE. Impressively, an unassisted PEC system is designed to generate H₂O₂ at the ZnO/Ti‐Fe₂O₃ photoanode while performing an oxygen reduction reaction (ORR) at the Fe(Co)‐NC cathode. The integrated system enables the average PEC H₂O₂ production rate of 0.275 µmol min⁻¹ cm⁻² without applying any additional bias. Moreover, an unassisted PEC cell obtains a long‐term stability of 100 h. This work demonstrates new possibilities in designing efficient and stable PEC assemblies using low‐cost earth‐abundant materials for light‐driven catalysis.