Influence of adjusted hydrophilic-hydrophobic lengths in sulfonated multiblock copoly(ether sulfone) membranes for fuel cell application

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2008-11, Vol.46 (22), p.7332-7341
• Main Authors: Nakabayashi, Kazuhiro, Matsumoto, Kazuya, Higashihara, Tomoya, Ueda, Mitsuru
• Format: Article
• Language: English
• Subjects: Applied sciences; atomic force microscopy; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; morphology; multiblock copolymers; Organic polymers; Physicochemistry of polymers; poly(ether sulfone); Polymer industry, paints, wood; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; proton conductivity; proton exchange membrane fuel cells; Technology of polymers; transmission electron microscopy
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.23038

Sulfonated multiblock copoly(ether sulfone)s applicable to proton exchange membrane fuel cells (PEMFCs) were synthesized by the coupling reaction of the hydroxyl-terminated hydrophilic and hydrophobic oligomers with different lengths in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender to investigate the influence of each length on the membranes' properties, such as water uptake, proton conductivity, and morphology. Multiblock copolymers with high molecular weights (Mn > 50,000, Mw > 150,000) were obtained under mild reaction conditions. The resulting membranes demonstrated good oxidative stability for hot Fenton's reagent and maintained high water uptake (7.3-18.7 wt %) under a low relative humidity (50% RH). Proton conductivity of all membranes at 80 °C and 95% RH was higher than that of Nafion 117 membrane, and good proton conductivity of 7.0 x 10⁻³ S/cm was obtained at 80 °C and 50% RH by optimizing the oligomer lengths. The surface morphology of the membranes was investigated by tapping mode atomic force microscopy (AFM), which showed that the multiblock copolymer membranes had a clearer surface hydrophilic/hydrophobic-separated structure than that of the random copolymer, and contributed to good and effective proton conduction.