(186h) Elucidating the Mechanism of PFOA Electrochemical Oxidation on Ti4O7 [112] Surface Using First Principles

Electrochemical oxidation is a promising method for per- and polyfluoroalkyl substances (PFASs) destruction, and has been shown to be successful experimentally at a pilot scale, particularly for perfluorooctanoic acid (PFOA). While existing literature reports decarboxylation as the initial electrochemical reaction step after a charge transfer, a detailed understanding of the reaction mechanism remains incomplete. This study employs density functional theory (DFT) to delve into the nuances of the electrochemical oxidation mechanism, aiming to provide novel insights into PFOA electrochemical oxidation reaction mechanism on Ti₄O₇ [112] surface. By including the electrode surface, explicit water, and external bias potential in the simulation, we aim to provide a more realistic representation of the electrochemical environment during the electrochemical oxidation reaction. Our findings reveal that water molecules near the ionic head group of the PFOA radical stabilizes it, and decarboxylation occurs with a ΔE of 0.025 eV in the presence of the bias potential of 3 V/SHE. Using the nudged elastic band method, the minimum energy pathway is determined, and subsequently the energy barrier for the first reaction step (decarboxylation) is found to be 0.53 eV. Furthermore, our DFT simulations identify the importance of the orientation of the PFOA radical in determining whether the C–C bond at PFOA head group dissociates. Our results suggest that the vertical orientation of PFOA is more favorable than others for the electrochemical reaction to proceed. Intriguingly, fluorine passivation of the surface facilitates the decarboxylation, irrespective of the PFOA radical’s orientation. Overall, this study advances the current knowledge of PFOA electrochemical oxidation on Ti₄O₇ electrocatalyst surfaces, focusing on the role of water molecules, PFOA radical orientation with respect to the surface, surface passivation, and external bias potential. As such, this study lays a foundation for future research and technological developments aimed at electrochemical remediation of PFAS contamination in water.