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 H 2 O 2 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 H 2 O 2 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 HO 2 · /O 2 ·– . This establishes a directional flow of cathodic electron toward H 2 O 2 and subsequently to Fe III (H 2 O 2 as shuttle), sustaining autonomous · OH generation until H 2 O 2 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.