Photo-electrochemical reduction of PFAS in complex water matrices

Per- and polyfluoroalkyl substances (PFAS) are among the most persistent and challenging environmental pollutants. Compared with conventional oxidative or homogeneous reduction processes, electrochemical and photoelectrochemical reduction (ER and PER) offer reagent-free routes for PFAS destruction but remain limited by poor PFAS removal and sluggish defluorination under cathodic conditions. Here, we report a Pd-decorated TiO₂ cathode that enables highly efficient photoelectrochemical degradation of perfluorooctane sulfonic acid (PFOS) under ambient conditions. Operando spectroscopy and density functional theory (DFT) calculations uncover a previously unrecognized mechanism in which cathodic potentials promote PFAS adsorption on TiO₂, while UV₂₅₄-excited Pd sites generate hot electrons that directly drive C-F bond cleavage or form hydrated electrons for indirect reduction. This dual-electron pathway leads to rapid and deep defluorination, outperforming previously reported ER and PER systems even in complex matrices such as reverse osmosis concentrate (ROC) and aqueous film-forming foam (AFFF)-impacted water. The study further demonstrates scalable single-chamber reactor designs and mesh-type cathodes, advancing the practical implementation of photoelectrochemical PFAS destruction technologies.