Phenolics-Reengineered Electron Flow in the Electro-Fenton Process for Energy-Conserving Decontamination

Electro-Fenton (EF) process suffers from energy and electron inefficiencies arising from residual H₂O₂ or excess Fe^II due to the stoichiometric mismatch between the two-electron oxygen reduction reaction (2e^- ORR) and ferric ion reduction (FRR) at a shared cathode. Here, we reengineered electron flow in the EF system to achieve on-demand Fe^II supply synchronized with H₂O₂ generation. A specific cathode spatially decouples 2e^- ORR from FRR, while phenolic coordination modulates the spin state of Fe^III to accelerate ferric-peroxide interactions. Quantum-chemical-calculation-assisted in situ spectroscopy reveals a ligand-to-metal charge-transfer chromogenic pathway involving a transient, high-spin phenolics-Fe^III-OOH intermediate, which undergoes homolytic Fe-O bond cleavage to yield Fe^II and HO₂^·/O₂^·-. This establishes a directional flow of cathodic electron toward H₂O₂ and subsequently to Fe^III (H₂O₂ as shuttle), sustaining autonomous ^·OH generation until H₂O₂ is exhausted. The reengineered EF system thereby achieves a 17-fold enhancement in ^·OH production at mg-level iron dosage, concomitant with 53.4% reduction in energy consumption relative to conventional EF systems. Finally, pairing this process with anodic hydroxylation of aromatics extends its applicability to the cost-effective treatment of wastewater containing diverse aromatic pollutants. Overall, this work provides a framework for integrating advanced 2e^- ORR cathodes into energy-efficient, redox-neutral systems for scalable wastewater decontamination.