Iodine-mediated proton-coupled electron transfer enables selective polymerization of organic pollutants in an oxidant-free electrocatalytic system.

Organic polymerization offers a sustainable water treatment approach that enables resource recovery, yet current oxidant-involved practices suffer from poor selectivity. We present an oxidant-free electrocatalytic system for phenolic pollutant polymerization via iodine-mediated proton-coupled electron transfer (PCET) with an iodine-enriched bismuth-oxyiodide-coated carbon cloth (I-BiOI@CC) anode, achieving 97.1% polymerization selectivity by converting pollutants into insoluble polymerized products. Mechanistic investigations demonstrate that I-BiOI@CC provides reversible redox mediation (3I⁻ ⇆ I₃⁻), enhancing pollutant-electrode interaction and accelerating interfacial charge transfer to facilitate PCET-oxidation of phenols to phenolic radicals that undergo polymerization through thermodynamically favored ortho C-O coupling. Polymerization kinetics depend on proton and electron transfer energetics, wherein phenols with stronger electron-donating capacity and weaker O-H bond strength promote the PCET process. The electrocatalytic system exhibits high energy and cost efficiency, demonstrates negligible biotoxicity, and shows excellent practicality. This work offers a promising proof-of-concept for future development of green and selective electrocatalytic processes for water decontamination.