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.