Synthesis and Characterization of Polyion Complex Membranes Made of Aminated Polyetherimide and Sulfonated Polyethersulfone for Fuel Cell Applications

Acid–base blends of sulfonated polyethersulfone (SPES) with pristine and aminated polyetherimide (APEI) are synthesized. Three blends polyethersulfone (PES)/polyetherimide (PEI), SPES/PEI, and SPES/APEI are prepared and characterized to evaluate their structural, morphological, mechanical, and other properties. Ion exchange capacity (IEC) of SPES/APEI and SPES/PEI blend membranes was determined to be 3.0 and 2.7 meq g−1, which is a substantial improvement over the 1.0 meq g−1 exhibited by unmodified PES/PEI blend. The proton conductivity of 0.093 S cm−1 displayed by SPES/APEI blend is found to be comparable to that of commercial Nafion membrane (0.056 S cm−1) and far superior to conductivities of 0.091 and 0.082 S cm−1 shown by SPES/PEI and PES/PEI blends, respectively. Further, water sorption observed in case of SPES/APEI and SPES/PEI blends was in the range 17–18% over a soaking time period of 12 hrs, which is ideal for proton conduction accompanied by low-membrane swelling. The methanol permeabilities of SPES/APEI and SPES/PEI blends are found to be 2.5 × 10−7 and 3.47 × 10−7 cm2 s−1, respectively. Compared to unmodified PES/PEI blend which revealed a methanol sorption of 12.3%, the modified blends SPES/PEI (9.6%) and SPES/APEI (7.5%) exhibited much lower methanol uptake over a sorption time of 12 hrs, indicating their capacity for low fuel bypass. The results demonstrate the promising potential of polymer blends made by combining a sulfonated polymer with an aminated polymer, such as SPES/APEI for fuel cell (FC) applications.