Enhanced mechanical durability of perfluorosulfonic acid proton-exchange membrane based on a double-layer ePTFE reinforcement strategy

Although widely used as proton-exchange membranes (PEMs), perfluorosulfonic acid (PFSA) membranes suffer from critical mechanical degradation under alternating wet/dry conditions. A common method for improving the mechanical durability of PFSA membranes is to intercalate single-layer expanded polytetrafluoroethylene (ePTFE). As reinforcement skeletons, the different numbers of ePTFE layers can be expected to have different effects on the mechanical durability of PFSA-based PEMs. In this study, double layers of ePTFE reinforcement are intercalated into PFSA ionomer to further enhance the mechanical durability of such membranes. The mechanical strength in directions A and B of the double-layer ePTFE reinforced membrane (DR-M) are 36.52 and 37.12 MPa, which are significantly higher than those (24.37 and 27.51 MPa) of the single-layer ePTFE reinforced membrane (SR-M). The area swelling rate of the DR-M is 11.91%, which is lower than that (15.53%) of SR-M. It is precisely due to the additional rigid ePTFE skeleton for the DR-M that the yield strength and modulus of the PFSA membrane are further improved, resulting in the higher resistance to plastic deformation. After 3000 cycles of alternating wet/dry conditions, DR-Ms exhibited no significant hydrogen crossover current increase (from 3.01 mA cm−2 to 2.98 mA cm−2), reduced H2/Air fuel cell performance attenuation (by 4.9%), smaller membrane impedance increase (by 6.2%), and reduced membrane structure failure (less cracks) compared with SR-Ms. In short, the described double-layer ePTFE enhancement strategy provided a fresh perspective for improving the mechanical durability of PEMs.