Electro-induced formation of FeWO4 interfacial layer enables heterogeneous radical activation in a green tungstate-driven electro-Fenton system

Efficient and sustainable degradation of antibiotic pollutants remains a major challenge in electrochemical advanced oxidation processes. Here, we report a tungstate-assisted electro-Fenton strategy that enables rapid removal of sulfamethoxazole (SMX) at near-neutral pH, in which the oxidant is generated in situ from dissolve oxygen to drive the electro-Fenton process without the need for external oxidants. Sodium tungstate (Na 2 WO 4 ), serving as both electrolyte and redox co-catalyst, facilitates homogeneous Fe 2+ /Fe 3+ cycling and in situ hydrogen peroxide generation, while also inducing the formation of a conformal FeWO 4 interfacial layer on the iron anode. Kinetic studies show a pseudo-first-order rate constant of 0.1560 min −1 , representing more than a 14-fold enhancement over conventional Na 2 SO 4 electrolyte. Comprehensive characterization using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Nyquist plots have indicated the dynamic nucleation of the FeWO 4 layer. Results of electron paramagnetic resonance (EPR) spectroscopy combined with radical scavenging tests revealed that the layer promotes surface-bound hydroxyl radical (•OH) generation, while suppressing iron dissolution and sludge formation. Additionally, UPLC-QTOF-MS/MS analysis identified key SMX degradation intermediates, confirming both homogeneous and interfacial oxidation pathways. Notably, Raman spectroscopy analysis detected the formation of peroxotungstate species (e.g., WO 2 (O 2 ) 2 2− ), indicating tungstate's participation in redox-mediated radical generation. Therefore, the co-designed electrolyte-electrode system integrates bulk-phase catalysis and interface-directed activation, achieving high degradation efficiency while reducing pollutant toxicity. This work offers a modular strategy for electrolyte-guided interfacial engineering and presents a practical design paradigm for electrochemical removal of sulfonamide antibiotics and similar micropollutants.