Recent Advances in Electrocatalytic Two-Electron Water Oxidation for Green H<sub>2</sub>O<sub>2</sub> Production

Abstract: Hydrogen peroxide (H2O2) is an environmentally friendly oxidant that has been widely used in water treatment, medical disinfection, chemical synthesis, and other industrial applications. However, traditional methods used to produce H2O2 consume significant amounts of energy and generate hazardous by-products, which limit their scope. On-site and on-demand electrocatalytic two-electron water oxidation chemistry is an attractive option for directly producing H2O2 from water; it also avoids the hazardous anthraquinone method, has fewer transportation costs and risks, and is integratable with renewable electricity. Despite these advantages, the two-electron water oxidation reaction (2e– WOR) still suffers from poor selectivity and activity due to a lack of mechanistic, material-design, and reactor-engineering understanding. This study summarizes recent advances in H2O2 electrosynthesis technology using the 2e– WOR. The catalytic 2e– WOR mechanism is first introduced with a focus on selectivity, activity, and stability. This reaction involves the electrocatalytic oxidation of water to produce H2O2, which can be further oxidized to O2. Selectivity is influenced by a variety of factors, including the electrocatalyst, pH, and electrolyte. Various quantitative H2O2 methods are discussed along with in situ characterization studies into the 2e– WOR aimed at better understanding the reaction process. Such methods include in situ Fourier-transform infrared spectroscopy and in situ Raman spectroscopy. Researchers are able to identify reaction intermediates and understand reaction mechanisms better using these techniques, thereby providing guidance for the design of more efficient electrocatalysts. In turn, various strategies for preparing high-performance electrocatalysts are summarized, including defect, doping, facet, and interfacial engineering methods. Mechanism-guided multiscale materials engineering can improve the activities and selectivities of electrocatalysts, thereby increasing H2O2 yields. In addition, device-level engineering, especially in relation to reactor and system innovations, is emphasized, which is important for improving reaction efficiency and reducing the cost of the 2e– WOR. Finally, current challenges and future opportunities in the 2e– WOR H2O2 electrosynthesis field are discussed. More effort directed at improving reaction selectivity, activity, and durability is required, along with exploring suitable application scenarios. The 2e– WOR is expected to become a more sustainable and efficient method for producing H2O2 facilitated by continuing progress in the materials science and electrochemical technology fields.