Electronic Delocalization Steering the Electron-Transfer Pathway in Fe–N/Se–C Catalyzed Peroxymonosulfate Activation

The sluggish kinetics of interfacial electron transfer, stemming from localized electronic structures, fundamentally limits the practical electron-transfer pathway (ETP) in peroxymonosulfate (PMS) activation. Herein, we demonstrate that engineering long-range electron delocalization through second-shell selenium (Se) doping can reconfigure the activation interface and decisively promote the ETP. A well-defined Fe single-atom catalyst with a Se-modified coordination environment (Fe–N4–Se4) was constructed, which induces pronounced electron delocalization, upshifts the Fe d-band center, and enhances orbital hybridization. This electronic restructuring strengthens PMS adsorption (from 1.66 to 4.00 eV) and drastically lowers the electron transfer barrier (from 2.935 to 0.728 eV). Consequently, the mechanism switches from radical-based processes on Fe–NC to a nearly exclusive ETP on the Se-doped catalyst (Fe–N/Se–C). This surface-mediated pathway enables rapid pollutant degradation (e.g., 4-chlorophenol, kobs = 0.279 min–1), exceptional environmental robustness (tolerance to anions, humic acid, wide pH range), and outstanding stability. This work provides atomic-level insight into how second-shell doping steers reaction pathways by modulating electronic delocalization, offering a new design paradigm for efficient non-radical oxidation systems.