Role of LiOH in\nAqueous Electrocatalytic Defluorination\nof Perfluorooctanoic Sulfonate: Efficient Li–F Ion Pairing\nPrevents Anode Fouling by Produced Fluoride

Per- and polyfluoroalkyl substances (PFAS) pose a significant\nenvironmental\nand health threat due to their high toxicity, widespread use, and\npersistence in the environment. Electrochemical methods have emerged\nas promising approaches for PFAS destruction, offering cost-effective\nand energy-efficient solutions. We established recently that electrocatalysis\nwith nonprecious materials enabled the complete defluorination of\nperfluorooctanesulfonate (PFOS) in aqueous 8.0 M LiOH. Here, we reveal\nthe mechanistic role of LiOH in the efficient aqueous electrocatalytic\nPFOS defluorination. Our results demonstrate that synergistic effects\nof high lithium and high hydroxide ion concentrations are essential\nfor complete PFOS defluorination. Two-dimensional NMR data of electrolytes\npost pulsed electrolysis provide experimental evidence for Li–F\nion pairing, which plays a crucial role in preventing anode fouling\nby produced fluoride, thus enabling sustained C–F bond cleavage.\nThis Li–F ion pairing was increased at high pH, and elevated\ntemperatures enhanced diffusion of Li–F ion pairs into the\nbulk electrolyte. High hydroxide ion concentrations additionally removed\nfluoride from the anode surface by competitive adsorption, corroborated\nby XPS data. Our findings provide quantitative mechanistic insights\ninto the electrocatalytic defluorination process and offer a general\nroute of enhancing the efficiency of anodic PFAS defluorination.