PFSA D50-U Proton-Exchange Gel Membrane for Symmetric Supercapacitors

Gel polymer electrolytes are key components in next-generation energy storage systems, particularly supercapacitors, due to their high ionic conductivity, mechanical robustness, and operational safety. Ionomer-based gels derived from perfluorosulfonic acid (PFSA) are particularly promising, as their nanophase-segregated morphology enables the formation of three-dimensional ionic clusters capable of absorbing and retaining aqueous electrolytes. In this study, the commercial PFSA D50-U (Thasar S.r.l.) membrane was investigated for the first time as a gel-state ionomer electrolyte and separator in symmetric supercapacitors using coconut shell-derived activated carbon (YP-80F Kuraray Co., Ltd.). The effects of cation type on gel swelling, ionic conductivity, and electrochemical performance were investigated using Na₂SO₄ and Li₂SO₄ aqueous electrolytes. The results showed that PFSA D50-U formed stable gel structures, resulting in low internal resistance, high specific capacitance, and excellent long-term cycling stability. These findings demonstrate that PFSA D50-U is a novel proton-exchange gel membrane with strong potential for high-performance symmetric supercapacitors and other gel-based energy storage devices.