Dynamic Reconstitution of Fe–In Dual-Atom Sites with Bridged Intermediate Adsorption for Selectively Electrochemical Oxygen Reduction to Hydroxyl Radicals

Abstract

The three-electron (3e–) oxygen reduction reaction (ORR) to hydroxyl radicals (HO•) represents an emerging strategy for water purification, yet achieving high selectivity remains challenging due to the scaling relationships between oxygen-containing intermediates. Herein, we report a Fe–In dual-atom catalyst (FeIn-DAC) with unique d-p orbital hybridization to tailor the electronic structure of Fe–In pairs for triggering optimal oxygen-bridged adsorption. Operando XANES and in situ Raman spectroscopy reveal that the initial Fe–N4 motif dynamically reconstitutes into Fe–N3 as the genuine active site upon ORR initiation, exposing more unsaturated sites for Yeager-type bridge-adsorbed *O–O* species. DFT calculations confirm that charge rearrangement within Fe–In pairs avoids excessively strong or weak electronic coupling with oxygen intermediates for steering 3e– ORR to HO•. As expected, the FeIn-DAC electrocatalytic system achieves a high HO• generation rate of 6.02 μmol L–1 min–1 and delivers ∼90% TOC removal for various antibiotic pollutants across wide pH ranges. A pilot flow-through device further verifies its practical applicability for real pharmaceutical wastewater treatment with ∼75%–85% TOC/COD removal during 24 h continuous operation. This study highlights potential-driven dynamic reconstitution of dual-atom catalysts for steering selective multielectron ORR under real working conditions.