Sulfonated poly(arylene ether sulfone) membranes based on biphenol for direct methanol fuel cells

A series of sulfonated poly(arylene ether sulfone) (PAES) were synthesized through direct aromatic nucleophilic substitution polycondensation of 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone(SDCDPS),(center dot)4,4-dichlorodiphenylsulfone (DCDPS) and 4,4-biphenol (BP). With increasing sulfonate groups in the polymer, water uptake, ion exchange capacity (IEC) and proton conductivities increased, resulting from enhanced membrane hydrophilicity. The membranes exhibited higher thermal stability up to 300 degrees C, verified by thermogravimetric analysis (TGA). A maximum proton conductivity of 0.11 S/cm at 50 mol% of sulfonation degree was measured at 300 degrees C, which is slightly higher than Nafion (R) 117 membrane (0.0908 S/cm). However, the methanol permeability of the PAES membrane was much lower than that of Nafion (R) 117 membrane. As a result, a single cell performance test demonstrated that PAES-BP with 50 mol% sulfonation degree exhibited higher power density than Nafion (R) 117.