Sulfonated Polyethersulfone (SPES) - Charged Surface Modifying Macromolecules (cSMMs) Blends as a Cation Selective Membrane for Fuel Cells

Polyethersulfone (PES) was sulfonated by chlorosulfonic acid and concentrated sulfuric acid. The pure sulfonated PES (SPES) and modified SPES membranes were prepared by blending with different charged surface modifying macromolecules (cSMMs) namely, SPES/DEG-HBS, SPES/PEG-HBS, and SPES/PPG-HBS. Membranes were characterized for their morphology, physical properties, and electrochemical properties in order to evaluate these membranes as cation exchange membranes. The blended membranes showed an increase in hydrophilicity, water uptake, and proton conductivity compared to the pure SPES membranes. The highest values of water uptake and proton conductivity were obtained for the SPES/PPG-HBS blended membrane. Morphological studies revealed that the nodule size and surface roughness also influenced the water uptake, apart from the additional -SO3H group. Among the modified membranes, the SPES/DEG-HBS blended membrane exhibited a lower methanol permeability value of 8.895 x 10(-8) cm(2) s(-1) than the corresponding SPES membrane. The other two cSMM blended membranes showed higher methanol permeability values than SPES but still a smaller value than Nafion 117. The highest selectivity ratio (i.e., ratio of proton conductivity to methanol permeability) was obtained with the SPES/DEG-HBS cSMM blended membrane. These results showed that the SPES/cSMM blended membranes have promise for possible use as a cation exchange membrane in fuel cells and electrolyzer applications.