Structure–Property Relationship of PEMs with Varying IEC under Different Humidity Environments

This study examines the influence of relative humidity (RH) on the physicochemical and electrochemical characteristic of perfluorinated sulfonic acid/PTFE-based polymer electrolyte membranes (PEMs) under varying ion exchange capacity (IEC) condition’s. Three commercial membranes Fumapem® F-950, F-1050, and F-14100 exhibiting IECs of 1.05, 0.95, and 0.71 meq/g, respectively, were systematically evaluated to understand their dielectric heavier across a RH range of 0–80%. Proton conductivity was measured using AC impedance spectroscopy, while DC conductivity was derived from Nyquist plots. Dielectric constant and loss tangent were analyzed to study charge relaxation and polarization behavior. Stress-strain curves were used to extract mechanical parameters such as toughness, resilience, elongation at break, Young's modulus, and also tensile strength. Dynamic mechanical analysis (DMA) provided insight into the temperature-dependent viscoelastic properties and glass transition temperature (Tg) of each membrane. Results show that increasing IEC enhances proton conductivity (and water uptake, but reduces mechanical stability. Dielectric analysis revealed strong dependence on both RH and IEC, with relaxation processes indicating mixed ionic conduction mechanisms. A strong correlation was observed between IEC and dynamic response, suggesting a trade-off between ionic transport efficiency and mechanical integrity. By balancing hydration, conductivity, and structural resilience under practical circumstances.