Lithium metal-mediated electrochemical degradation of per- and poly- fluoroalkylsubstances (PFAS)

Per- and poly-fluoroalkyl substances (PFAS) have significant environmental and health hazards. Unfortunately, current PFAS degradation routes require higher temperatures or highly corrosive conditions and/or lead to incomplete defluorination and generation of shorter alkyl chains. Fortunately, fluorinated compounds are highly vulnerable to reduction. Inspired by the lithium metal battery literature, we develop an ambient temperature and pressure electrochemical degradation process that takes advantage of reactive metals and highly reducing environments. We show that electrodeposited lithium metal can enable 95% degradation and 94% defluorination of a long chain PFAS, perfluorooctanoic acid (PFOA) without forming any shorter C2-C7 PFAS as end products. More importantly, we show mineralization to LiF. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we reveal the degradation mechanism and show that electron transfer from Li to PFOA leads to rapid C-F bond cleavage, the formation of fluoride, and carbon chain fragments. We expand the scope to other PFAS compounds and of the 33 PFAS compounds tested, 22 demonstrated degradation amounts exceeding 70% (with some degradation up to 99%), and complete mineralization to inorganic fluorides. Finally, we use the mineralized F− as a fluorine source for the synthesis of fluorinated non-PFAS compound such as ethane sulfonyl fluoride to complete a circular fluorine loop from waste to valuable product. Our work showcases a novel electrochemical approach that borrows from the battery literature to solve challenges in environmental remediation.