Flexible but strong, colorless, and transparent polyvinylidenefluoride-polystyrene sulfonic acid (PVDF-PSSA) proton exchange membranes (PEMs) were synthesized by blending PVDF and copolymers of poly(tetrabutylammonium styrene sulfonate) (PTBASS) having small (≤ 10%) mole fractions of 4-chloromethylstyrene (CMS) as well as styrene or MMA. The PTBASS copolymer precursors were synthesized through conventional radical copolymerizations of TBASS and CMS with minor (≤ 20%) comonomer mole fractions. Homogenous blends of PVDF-PTBASS copolymers were formed by dissolution in DMF and evaporation at 165 °C and a controlled thermal crosslinking through a sulfonate-catalyzed benzylation. The PVDF-PTBASS blends were optically transparent at 165°C and remain so after rapid thermal quenching and near quantitative proton exchange using 1.0 M aqueous H<sub>2</sub>SO<sub>4</sub> along with surfactant to give the PVDF-PSSA copolymer membranes. Transmission electron microscopy (TEM) confirms the presence of ultra-small (£ 1 nm) hydrophilic domains.  The membranes were characterized by elemental analysis, water uptake, ion exchange capacity (IEC), proton conductivity, methanol permeability and mechanical properties. The performance of the membranes in a single-cell direct methanol fuel cell (DMFC) was evaluated by fabricating membrane-electrode assemblies and compared against Nafion-117 using similar procedures and testing conditions and were found to have a moderate to good tolerance to high methanol (17 M) concentrations delivering good power densities.

Nanoporous polystyrene sulfonic acid blended membranes for direct methanol fuel cells

ACS Fall 2021

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