Fabrication and characterizations of Zn-doped SnO2-Ti4O7 anode for electrochemical degradation of hexafluoropropylene oxide dimer acid and its homologues

Hexafluoropropylene oxide dimer acid (HFPO-DA) and its homologues, as perfluorinated ether alkyl substances with strong antioxidant properties, have rarely been reported by electrooxidation processes to achieve good results. Herein, we report the use of an oxygen defect stacking strategy to construct Zn-doped SnO2-Ti4O7 for the first time and enhance the electrochemical activity of Ti4O7. Compared with the original Ti4O7, the Zn-doped SnO2-Ti4O7 showed a 64.4% reduction in interfacial charge transfer resistance, a 17.5% increase in the cumulative rate of •OH generation, and an enhanced oxygen vacancy concentration. The Zn-doped SnO2-Ti4O7 anode exhibited high catalytic efficiency of 96.4% for HFPO-DA within 3.5 h at 40 mA/cm2. Hexafluoropropylene oxide trimer and tetramer acid exhibit more difficult degradation due to the protective effect of the -CF3 branched chain and the addition of the ether oxygen atom leading to a significant increase in the C-F bond dissociation energy. The degradation rates of 10 cyclic degradation experiments and the leaching concentrations of Zn and Sn after 22 electrolysis experiments demonstrated the good stability of the electrodes. In addition, the aqueous toxicity of HFPO-DA and its degradation products was evaluated. This study analyzed the electrooxidation process of HFPO-DA and its homologues for the first time, and provided some new insights.