Cascaded Fe-*OOH and Co-*H ₂ O ₂ Intermediates on Fe–Co Dual Sites for Orchestrated O ₂ 3-Electron Electro-Fenton Pathways

The heterogeneous electro-Fenton (HEF) process has emerged as a promising advanced oxidation technology for wastewater remediation, yet an insufficient mechanistic understanding of the interfacial electron transfer processes and intermediate evolution still limits further improvement of efficient <i>in situ</i> hydroxyl radical (^•OH) generation. Herein, we design Fe-Co bimetallic oxide catalysts for the HEF reaction via a novel 3-electron pathway and identify that the synergistic Fe-Co dual sites promoted the formation of critical intermediates: Fe-*OOH during the O₂ reduction and Co-*H₂O₂ during H₂O₂ activation. <i>In situ</i> Raman spectroscopy that directly captured these intermediates on catalyst surfaces, together with density functional theory (DFT) calculations, confirms that the Fe and Co sites facilitate the direct interfacial conversion of adsorbed H₂O₂ to ^•OH via optimizing reaction kinetics that Fe predominantly drives the 2-electron O₂ to H₂O₂ step, while Co efficiently activates 1-electron H₂O₂ to ^•OH. In a continuous-flow reactor, the Fe-Co catalyst achieved ∼80% total organic carbon (TOC) and chemical oxygen demand (COD) removal over 15 h, with an energy efficiency of 0.04 kW·h·g^-1. This work provides fundamental insights into dual sites in boosting the HEF reaction at the molecular level, establishing a design principle of cathodic catalysts for environmental remediation.