Structural influence of hydrophobic component in sulfonated poly(sulfide sulfone imide) copolymers on polymer electrolyte membranes

Abstract

Recent research in Polymer electrolyte membrane fuel cell (PEMFC) has focused on the development of membranes that operates at medium-high temperature (100 200 oC). The medium-high temperature PEMFC offer several advantages, such as low CO catalyst poisoning, higher efficiencies, heat management, high fuel diffusion rate and cost. However, relatively low glass transition temperature and poor thermal stability of Nafion limits operating at high temperature. To replace perfluorosulfonic acid ionomer, sulfonated hydrocarbon membranes, acid-doped PBI membranes, inorganic additive composite membranes, pore-filling reinforced membranes and blend membranes have been studied. In particular, sulfonated hydrocarbon membranes have been studied for medium temperature applications (< 120 oC) to overcome degradation of perfluorosulfonic acid membranes and acid leakage of acid-doped PBI membranes.In this study, sulfonated poly(sulfide sulfone imide) copolymers were successfully synthesized, and the polymer electrolyte membranes were characterized with physical properties and electrochemical performances. The obtained new polymers containing flexible sulfide bond and six-membered imide ring were synthesized in m-cresol, at 180 oC, by random polycondensation. Two types of membranes were prepared by using different non-sulfonated diamine to verify effects of the hydrophobic component. IEC values were controlled by the degree of sulfonation ranging from 50 to 80 %. All the membranes showed good thermal stability and high mechanical strength. Dimensional stablility of membranes exhibits excellent properties. Proton conductivity of two types of membranes composed of different non-sulfonated diamine shows different behavior and displays relatively high correlation with dimensional stability. Furthermore, well separated hydrophilic/hydrophobic membranes morphology was observed and the single cell performance was also tested (at 80 120 oC) and reported.