Multiblock sulfonated poly(arylene ether sulfone)s with fluorenyl hydrophilic moieties for PEMFC applications

Multiblock sulfonated poly(arylene ether sulfone) (MB-SPAES) ionomers containing fluorenyl hydrophilic moieties were synthesized and converted into proton exchange membranes (PEMs) through solution casting, as well as other two types of MB-SPAES membranes containing hydrophilic biphenyl and hexafluoroisopropyl diphenyl moieties for the comparison. Chemical structures of the MB-SPAES ionomers were confirmed by H-1 NMR spectrometer. Fundamental physical properties were characterized based on the ionic group content, the hydrophilic/hydrophobic block structure and length, including ion exchange capacity (IEC), water uptake, size change, mechanical property, proton conductivity, hydrolytic stability and fuel cell performance. All the obtained MB-SPAES membranes were transparent and mechanical ductile, suitable for PEM applications. Water uptake and size change results showed that the MB-SPAES membranes containing fluorenyl hydrophilic moieties absorbed less water and swelled smaller in water than the other two types at similar IECs, indicating their better dimensional stability. Proton conductivity and hydrolytic stability results indicated that the fluorenyl hydrophilic moieties were also favorable to gain better proton conductivity and hydrolytic stability.