Electrochemical Oxidation of Perfluorobutanoic Acid and Ultrashort-Chain Perfluorocarboxylic Acids

Electrochemical oxidation of per- and polyfluoroalkyl substances (PFAS) with ≤3 perfluorinated carbons, including perfluorobutanoic acid (PFBA), perfluoropropionic acid (PFPrA), and trifluoroacetic acid (TFA), was investigated using a Ti4O7 reactive electrochemical membrane (REM) anode in an inert NaClO4 electrolyte. This study demonstrated mineralization of all PFAS to fluoride and detailed their anodic reactivity. Oxidation of PFBA, PFPrA, and TFA occurred at potentials ≥3.2 V versus the standard hydrogen electrode (V/SHE), reaching mass transfer limited rates at ≥4.2 V/SHE. Applying 4.7 V/SHE, ≥99% of each PFAS was transformed within a hydraulic residence time of 53 s, and removal was enhanced 1.5-fold due to electromigration of PFAS anions toward the anode. The local pH drop at the anode converted a fraction of the PFAS to their acidic forms, which exhibited lower reactivity due to an increase in their estimated standard redox potentials (E0) by more than 1.0 V, as predicted by density functional theory. Butler–Volmer modeling captured both the activation-controlled and mass transfer limited regimes with transfer coefficients between 0.13 and 0.20, while acid/anion co-occurrence prevented exact determination of E0 and exchange current densities. Finally, sulfate competition during electrochemical oxidation of a synthetic semiconductor fab effluent reduced PFAS mineralization efficiency by >20%, exhibiting the challenge of designing Ti4O7 REM systems to avoid ultrashort-chain PFAS accumulation.