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)/Ti3C2Tx 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.