Preparation and characterization of high-durability zwitterionic crosslinked proton exchange membranes

The present paper describes the development of a novel proton exchange membrane comprising a poly (styrene sulfonic acid-co-4-vinylpyridine) copolymer that was crosslinked with a haloalkyl crosslinker through the formation of ionic bonding linkages. The nucleophilic substitution of these crosslinked membranes as well as a model reaction between pyridine and 1-bromobutane was confirmed by nuclear magnetic resonance (NMR). Tough and flexible membranes of a high mechanical strength were prepared. They demonstrated very elevated thermal, hydrolytic and oxidative stabilities as compared to other sulfonated polymers. The crosslinked membrane composed of zwitterionic molecules with a crosslinking fraction of 90.3, denoted SP-1, exhibited a proton conductivity of ca. 7.1 × 10 −2 S cm −1 at 30 °C under 90% relative humidity; a value comparable to that of Nafion 117. Moreover, the crosslinked SP-1 membrane possessed the highest selectivity for methanol fuel cells (3.38 × 10 5 S cm −3 s), approximately five times that of Nafion 117, thus implying its potential for practical use in high-energy-density devices.