Perfluorosulfonic acid (PFSA) ionomers are key materials for electrochemical devices such as fuel cells, water electrolyzers, and flow redox batteries due to their remarkable proton conductivity, chemical and mechanical stability. The morphology and properties of the PFSA membranes are dictated by the self-assembled nanostructure in dispersion that is used for membrane fabrication. In this work, rheological analysis and structural characterization techniques are used in combination to spotlight how counterions (H + vs. Na + ) and solvents (IPA/water vs. DMF) cooperatively influence the microstructure and rheology of PFSA in solution. It is seen that PFSA-H exhibits higher viscosity in IPA/water, which is attributed to the formation of secondary aggregates from nanorods crosslinked by H 3 O + . In DMF, proton dissociation is reduced and PFSA adopts a coil conformation that leads to a lower viscosity. This work provides a comprehensive understanding of the synergistic role of counterions and solvents in controlling the solution state nanostructure beyond PFSA chain assembly, which turns out to be the critical reason for rheology property change, and provides a useful theoretical basis for optimizing ionomer and solvent selections.
Hao et al. (Sun,) studied this question.