Selective Oxygen Activation to Reactive Oxygen Species on a Carbon Layer-Encapsulated Cu x O Electrocatalyst for Water Purification.

In situ synthesis of reactive oxygen species (ROS) on demand via oxygen activation (OA) is significant in biological, chemical, and environmental fields. Thus, the design of OA catalysts with adequate reactivity, durability, and selectivity is critical but challenging. Here, we report a Cu x O@C core@shell photoelectrode prepared by encapsulating Cu/Cu 2 O/CuO into a carbon layer through anodic electropolymerization (electrophoresis-coupled self-assembly of carbon quantum dots). Theoretical prediction and experiments indicate that the carbon layer can effectively facilitate optical trapping and charge transfer, thus promoting photoelectric conversion and anti-photocorrosion performance of Cu x O@C. The inner Cu x O core acts as an electron reservoir and continuously injects electrons into the outer carbon layer shell, and the carbon atoms adjacent to oxygen-enriched functional groups (C-O-C and -COOH) in the electron-rich carbon layer work as the reactive sites to adsorb O 2 and donate electrons to the antibonding orbital [lowest unoccupied molecular orbital (π*)] of dioxygen. Optimized adsorption and hydrogenation of the critical intermediates (*O 2 , *OOH, and *H 2 O 2 ) and thermodynamically tunable O-O bond cleavage enable O 2 being selectively reduced to the superoxide anion and hydroxyl radical via the mixed multielectron processes consisting of one- and three-electron pathways. Sulfamethoxazole, an emerging refractory organic contaminant widely present in the environment, can be effectively degraded (∼100% removal) in such an electrochemical platform, benefiting from the abundant ROS generated in situ. Our findings demonstrate an innovative strategy to develop highly efficient and selective OA catalysts for practical water purification.