Anchoring Variable-Valence Metal Ions to Enhance the Chemical Stability of Proton-Exchange Membranes

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