Redox-gated polyvinylferrocene interfaces for cathodic peroxymonosulfate activation

Electrochemical advanced oxidation can intensify contaminant removal while avoiding consumable metal catalysts, but cathodic activation of anionic peroxymonosulfate (PMS, HSO₅^-) is limited by electrostatic exclusion from negatively polarized interfaces. Here, we constructed a polyvinylferrocene-modified biochar (PVF-BC) cathode operated by a two-stage potential program. At 0 V, reaction of surface-bound ferrocene (Fc) with PMS partially formed ferrocenium (Fc⁺), whereas subsequent operation at -1.2 V accelerated cathodic PMS reduction. Component-resolved controls, X-ray photoelectron spectroscopy, electrochemical measurements, spin-trapping experiments, kinetic modelling, and density functional theory calculations were collectively consistent with complementary roles of interfacial charge regulation and cathodic electron transfer. The system removed >90% of bisphenol A (BPA) during the first ten cycles and retained approximately 80% removal after 25 cycles, operated across pH 3-7 with an electrical energy (applied voltage only) per order of approximately 0.1 kWh m^-3 order^-1. In a fivefold enlarged bench reactor fed with 100-fold-diluted coal-chemical wastewater, phenol, p-cresol, and m-cresol removals reached 70.0%, 80.9%, and 81.2%, respectively. These results identify redox-active interfacial charge regulation as a promising route to mitigate anion-transport limitations during cathodic PMS activation.