Metal-Free Electrocatalysts for H2O2 Electrosynthesis: From Sites Identification to Electrochemical Advanced Oxidation Process

Carbonaceous materials, especially the metal-free carbons, have attracted widespread attention owing to their risk-free nature with metal dissolving during the electrocatalysis process, but their further developments are still hindered by missing a suitable scenario on practical applications. Herein, we demonstrate a successful case of using the oxygen-containing-groups-modified carbons for the H₂O₂ electrosynthesis and the derivative electrochemical advanced oxidation process. The active sites with the more C─O rather than C═O groups are easily obtained by controlling the temperature and time in the wet chemical treatment. Identified by theoretical calculations and electrochemical testing, the modified carbons with the highest ratio of C─O/C═O groups exhibit high activity with above 90% H₂O₂ selectivity over the entire potential during 2e-transfer oxygen reduction reaction, attributing to their enlarged charge delocalization. In addition, the corresponding gas diffusion electrodes with the high-speed and high-stability H₂O₂ electrosynthesis (2.78 µg s⁻¹ cm⁻² with the above 80% current efficiency) are applied for the electro-peroxone process on the simulant and practical phenolic wastewater, where the chemical oxygen demand removal reaches above 90%. The long-term operation in the harsh electrochemical environment for over 200 h also confirms its great potential for practical electrochemical applications.