The strong metal-support interactions induced electrocatalytic three-electron oxygen reduction to hydroxyl radicals for water treatment.

As a promising environmental remediation technology, the electro-Fenton (EF) process is mainly limited by the two rate-limiting steps, which are HO generation and activation. The electrocatalytic three-electron oxygen reduction reaction (3e ORR) can directly activate oxygen to hydroxyl radicals (•OH), which is expected to break through the rate-limiting steps of the EF process. However, limited success has been achieved in the design of 3e ORR electrocatalysts. Herein, we propose Cu/CoSe/C with the strong metal-support interactions to enhance the 3e ORR process, exhibiting remarkable reactivity and stability for •OH generation. Both experiment and DFT calculation results reveal that CoSe is conducive to the generation of HO. Meanwhile, the metallic Cu can enhance the adsorption strength of *HO intermediates and thus promotes the one-electron reduction to •OH. The Cu/CoSe/C catalyst exhibits the electron-transfer number close to 3.0 during the ORR process, and exhibits the outstanding •OH generation performance, achieving a higher apparent rate constant (6.0 times faster) toward ciprofloxacin compared with its analogy without the SMSI effect. Our work represents that the SMSI effect endows Cu/CoSe/C high activity and selectivity for •OH generation, providing a unique perspective for the design of a high-efficiency 3e ORR catalyst.