Recent Progress on the Catalysts and Device Designs for (Photo)Electrochemical On-Site H₂O₂ Production

Low-cost and on-site H2O2 production is desirable for industrial and civilian usage. (Photo)electrochemical H2O2 production is proposed to be a safer, greener, and cheaper strategy for on-site H2O2 production as compared to the conventional anthraquinone process and the direct thermal synthesis. However, the efficiency, selectivity, and durability of the (photo)electrochemical H2O2 production devices are still not satisfactory. Therefore, there is an urgent need to revisit the (photo)electrocatalyst and device designs for (photo)electrochemical on-site H2O2 production, thus to rationalize the research thoughts and provide valuable guidance. This review comprehensively summarizes and discusses the mechanism of two-electron oxygen reduction reaction (2e(-) ORR) and two-electron water oxidation reaction (2e(-) WOR) for H2O2 production, and the current research status on the (photo)electrocatalysts and (photo)electrochemical devices. In particular, the pros and cons of the four types of (photo)electrochemical device designs, which are Type I (2e(-) ORR + oxygen evolution reaction), Type II (2e(-) ORR + hydrogen oxidation reaction), Type III (2e(-) WOR + hydrogen evolution reaction) and Type IV (2e(-) WOR + 2e(-) ORR), are discussed in detail. Finally, a practical perspective on the future research directions for the on-site (photo)electrochemical H2O2 production based on the technical challenges of this technique is provided.