Ionic Liquids: A Novel Route for Sustainable Recycling of Nafion from Proton Exchange Membrane Fuel Cells

We report a breakthrough strategy for recycling perfluorosulfonic acid (PFSA) polymers, such as Nafion, using tailored ionic liquids (ILs). Imidazolium- and phosphonium-based ILs enabled efficient dispersion of Nafion within 6 h at 180 °C, with performance increasing with IL hydrophobicity and alkyl chain length. Two sequential regimes were identified: initial cation exchange followed by IL diffusion enhanced by plasticization, ultimately driving membrane reorganization. Dispersion was triggered once the membrane volume expansion exceeds ∼180%, underscoring strong IL–polymer affinity. Swelling kinetics deviated from Fickian behavior, indicating complex physicochemical interactions. Ethanol washing and acidification enabled partial IL removal and served as probes for IL localization and binding strength, as confirmed by FTIR. Multiscale structural analyses provide mechanistic insight: small-angle neutron scattering reveals pronounced swelling of ionic domains, while wide-angle X-ray scattering shows IL penetration into amorphous regions with irreversible rearrangements, with crystalline domains remaining preserved. Among the ILs tested, C1C8ImCl and P66614Cl offer the best compromise between dispersion efficiency and extractability. These findings highlight ILs as dual-function agents─both effective PFSA dispersants and potential functional additives─thus enabling high-yield recovery and upcycling of PFSA. This approach opens sustainable, closed-loop pathways for electrochemical energy technologies.