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 H 2 O 2 , depending on the semiconductor to initiate two‐electron water oxidation into hydrogen peroxide (H 2 O 2 ). 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 H 2 O 2 . Herein, Ti‐doped Fe 2 O 3 photoanode with the modification of ZnO passivation layer (ZnO/Ti‐Fe 2 O 3 ) for PEC H 2 O 2 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 H 2 O 2 at the ZnO/Ti‐Fe 2 O 3 photoanode while performing an oxygen reduction reaction (ORR) at the Fe(Co)‐NC cathode. The integrated system enables the average PEC H 2 O 2 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.