Perfluorosulfonic-acid (PFSA) membranes are used as the solid-electrolyte in fuel cells where they promote water transport, ionic conductivity, gas separation, and mechanical support. All of these functionalities are expected to be related to the nanostructure and chemical properties of the membrane. It is of great interest to understand how these properties change with degradation during cell operation. This study investigates the changes in water sorption and morphology of membranes that were degraded in various degradation modes based on accelerated-stress testing (AST) protocols. Our findings show that upon degradation, water uptake of the membrane decreases, which is consistent with the observed increase in its backbone crystallinity as inferred from wide-angle X-ray scattering (WAXS) experiments. Reduced uptake accompanied by increased crystallinity in chemically degraded membranes suggests degradation-induced changes in structure-property relationship of PFSA membranes similar to annealing-induced changes.
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