Elucidating the Impact of the Electrocatalyst Surface and Applied Potential on the Decarboxylation of the PFOA Radical on the Ti₄O₇ [112] Facet Using DFT Simulations

The electrochemical oxidation of perfluorooctanoic acid (PFOA) begins with charge transfer followed by decarboxylation, but the reaction mechanism on electrocatalyst surfaces remains poorly understood. This study employs density functional theory (DFT) simulations with an explicit solvation model to investigate the effects of the electrocatalyst surface composition and applied potential on PFOA radical decarboxylation on the Ti₄O₇ [112] facet. Results indicate that while decarboxylation is thermodynamically favorable in vacuum, it is hindered by water molecules surrounding the ionic group of PFOA. The process is highly dependent on the radical’s orientation, surface interactions, and electrode composition, with F-terminated surfaces being more effective than O-terminated ones. Although a vertical orientation enhances decarboxylation, surface binding suppresses the reaction even in this favorable configuration. Ab initio molecular dynamics simulations reveal that decarboxylation precedes defluorination under an applied potential of 3.08 V/SHE. Climbing image nudged elastic band calculations suggest that the applied potential reduces the activation barrier by 0.34 eV and lowers the reaction energy by 1.05 eV. These insights enhance our understanding of PFOA degradation mechanisms, aiding in the design of optimized electrode materials for per- and polyfluoroalkyl substance (PFAS) remediation via electrochemical oxidation.