Anchoring Variable-Valence\nMetal Ions to Enhance the\nChemical Stability of Proton-Exchange Membranes

To prevent the chemical degradation of proton-exchange\nmembranes\n(PEMs) caused by free-radical attacks, in this study, magnetron sputtering\ntechnology was employed to deposit Ce, Ti, and Mo elements as free-radical\nscavengers (FRSs) onto the surface of polytetrafluoroethylene to fabricate\nperfluorosulfonic acid/polytetrafluoroethylene-M (PFSA/PTFE-M; M =\nmetal ion) composite membranes. By controlling the injection dose,\na surface layer of a radical-quenching-ion barrier with controlled\ndepth and dosage was successfully fabricated. After 96 h Fenton testing,\nthe residual weight and the fluoride ion release rates of the modified\ncomposite membranes were higher and lower than those of the pristine\nPFSA/PTFE membrane, respectively. Significantly, the PFSA/PTFE-Mo-3\nmin membrane exhibited the best chemical stability, highest residual\nweight of 88.75%, and lowest fluoride ion release rate of 0.414 mmol/g.\nFurthermore, after accelerated aging tests, the proton conductivity\nof the modified enhanced composite membranes was higher than that\nof the pristine PFSA/PTFE membrane, which was opposite to the trend\nobserved before the accelerated aging tests. This indicates that introducing\nmetal ions via magnetron sputtering is an effective method to enhance\nthe chemical stability of PEMs.