Fluorine-Substituent-Containing Sulfonated Poly(arylene ether) Membranes with Enhanced Proton Conductivity and Dimensional Stability for Proton Exchange Membrane Fuel Cells
Abstract
A series of fluorine-substituent-containing sulfonated poly(arylene ether) membranes was synthesized and evaluated as proton exchange membranes for fuel cell applications. Fluorinated difluoro monomers were first reacted with three different diol monomers through nucleophilic polycondensation to obtain 4FP4-series polymers, followed by controlled sulfonation to produce six S4FP4-series membranes with different ion exchange capacities and microphase-separated morphologies. FT-IR, 1H-NMR, and 19F NMR spectroscopy confirmed the chemical structures of monomers, polymers, and sulfonated polymers. The resulting polymers exhibited good film-forming ability and high thermal stability. The sulfonated membranes showed ion exchange capacities of 1.74–2.80 mmol/g, water uptake of 24.7–116.3%, and favorable dimensional stability under elevated temperature. Most S4FP4 membranes exhibited proton conductivities higher than that of Nafion 211. In particular, S4FP4a (IEC of 1.74) achieved a proton conductivity of 262 mS cm−1 at 80 °C and 95% RH and a maximum fuel cell power density of 1.07 W cm−2, outperforming Nafion 211. TEM analysis revealed that fluorine substitution promoted effective microphase separation and continuous mesoscale aggregated domain. These results demonstrate that fluorinated sulfonated poly(arylene ether)s are promising candidates for high-performance proton exchange membranes.