Structure–morphology–property relationships in sulfonated poly(arylene ether)s proton exchange membranes: impact of hydrophobic segment engineering

Abstract

Sulfonated poly(arylene ether)s (SPAEs) are promising alternatives to perfluorosulfonic acid membranes, but balancing proton conductivity, dimensional stability, oxidative stability, and fuel resistance remains challenging. Herein, four SPAE copolymers with similar hydrophilic segments and comparable ion exchange capacity values but distinct representative hydrophobic segment architectures, including fluorinated, low-fluorinated, amorphous hydrocarbon, and semi-crystalline hydrocarbon structures, were prepared to establish comparative structure–morphology–property correlations. The fluorinated membranes exhibited distinct hydrophilic/hydrophobic microphase separation and relatively high proton conductivity, but their methanol resistance was limited, especially for the highly fluorinated F-SPAE membrane. In contrast, the amorphous hydrocarbon-based A-SPAE membrane showed improved methanol resistance but less connected hydrophilic domains, resulting in lower proton conductivity and weaker dimensional/oxidative stability. Among the four membranes, the semi-crystalline hydrocarbon-based SC-SPAE membrane showed the most balanced properties under the present testing conditions. It displayed continuous hydrophilic channels, a high in-plane proton conductivity of 0.126 S cm−1 at 80 °C, low water swelling of 8.32% at 80 °C, high residual weight retention of 97.46% after Fenton treatment, and the lowest methanol permeability of 2.38 × 10−7 cm2 s−1. In comparative fuel-cell tests, SC-SPAE delivered maximum power densities of 283.72 mW cm−2 in H2/O2 fuel cells and 18.91 mW cm−2 in direct methanol fuel cells using 10 M methanol. These results indicate that semi-crystalline hydrocarbon-based hydrophobic segment architectures provide a useful route to balance proton transport, membrane stability, and methanol resistance in SPAE-based proton exchange membranes.