Electrocatalytic removal of Hexafluoropropylene oxide dimer acid (HFPO-DA) in water: “Buttering on both Sides”

Hexafluoropropylene oxide dimer acid (HFPO-DA), an emerging persistent pollutant, has been prevalently utilized as an alternative to perfluorooctanoic acid (PFOA). Analogous to PFOA, HFPO − DA presents remarkable resistance against degradation by conventional technologies. In this study, we prepared Ce doped PbO 2 anode (Ce-PbO 2 ) and paired it with cathode to form redox system for the degradation of HFPO-DA in water. The results showed that the degradation rate of HFPO-DA over Ce-PbO 2 was as high as 1.67 × 10 −2 min −1 , much higher than that of Boron-doped diamond electrode (BDD, 6.84 × 10 –3 min −1 ). The Ce-PbO 2 anode also has the theoretical lifetime as high as 82.7 years. Free radical quenching experiments indicated that both reactive oxygen species (ROS) and reductive radicals contributed to the degradation of HFPO-DA. These degradation reactions start from a direct electron transfer, followed by electroreduction and a series of free radical reactions including decarboxylation, ether bond cleavage, and the “4A” processes (generation of Alkyl radicals, Alcohols, Acyl fluorides, and Acids in sequence) until it is decomposed into small molecules. Meanwhile, new intermediates (CF 3 CF 2 CF 2 OCF 3 CH•) generated by cathodic H• are dominating the reductive reaction during the electrochemical process. This “buttering bread on both sides” redox mechanism deepens the understanding of the degradation process of HFPO-DA and provides an efficient treatment strategy.