Electrooxidation of Perfluorocarboxylic Acids by an Interfacially Engineered Magnéli Phase Titanium Oxide (Ti₄O₇) Electrode with MXene

Electrochemical advanced oxidative processes (EAOPs) offer promising pathways for the eradication of persistent organic pollutants, such as perfluoroalkanesulfonates (PFSAs) and perfluorocarboxylic acids (PFCAs). Herein, we demonstrated a hybrid electrocatalyst of Magnéli phase titanium oxide (Ti₄O₇)/Ti₃C₂T_x MXene for EAOP. The perfluorooctanoic acid (PFOA) degradation rate in batch tests by the Ti₄O₇/MXene electrode was 2.21 × 10^-2 min^-1, three times faster than that of the Ti₄O₇ electrode (0.76 × 10^-2 min^-1). This hybrid Ti₄O₇/MXene electrode significantly lowered the interfacial charge-transfer resistance from 54.36 to 7.18 Ω compared with the Ti₄O₇ electrode. The Ti₄O₇/MXene electrode also exhibits excellent stability as tested by 10 consecutive cycles for 30 h under a DC current of 10 mA·cm^-2 and reached a stable PFAS degradation (98.1-9.2%). Some degradation isomers and intermediates with lower fluorinated chain lengths were detected. In addition, density functional theory (DFT) calculations indicate a greater charge transfer for PFOA and a lower adsorption energy for hydroxyl radicals (•OH) on Ti₄O₇/MXene in comparison with the pristine Ti₄O₇, which would facilitate the diffusion of radicals and oxidative reactions with PFCAs. A standardized electric energy consumption per log removal of PFCAs (EE/O) was found to be only 8-14 kWh m^-3, which is among the lowest level of the current literature data. The integration of these hybrid nanomaterials brings forth a unique synergy that holds the capacity to drive enhanced catalytic activity, thereby contributing significantly to the field’s pursuit of efficient pollutant removal and environmental remediation.