Sulfonated polystyrene/polyvinyl chloride composite membranes for PEMFC applications

The sulfonated polystyrene (SPSt)/polyvinyl chloride (PVC) composite electrolyte membranes were prepared via styrene-impregnated polymerization within PVC matrix and subsequent sulfonation. The propagated polystyrene chains were interpenetrated with those of the PVC film, and hence the two components were completely compatible. The effects of some preparation parameters, including monomer solution composition, polymerization and sulfonation conditions, on membrane performance were investigated. It was found that crosslinking with DVB improved oxidative stability, while excess crosslinking might lead to decrease in the proton conductivity. Polymerization should be carried out at 80 °C for more than 8 h; otherwise the produced polystyrene had relatively low molecular weight and might leach out of the membrane. The higher concentration of chlorosulfonic acid or the higher sulfonation temperature caused side reactions, which led to decrease in proton conductivity as well as slight improvement in oxidative stability. Furthermore, repetitious polymerization under hot-pressing plates further improved proton conductivity with slight increase in membrane thickness. Preliminary data in single cell test showed that the prepared membrane had comparable performance with commercial Nafion. This study demonstrates that an inexpensive polymer electrolyte membrane suitable for low-temperature PEMFC applications can be prepared easily by styrene/DVB-impregnated polymerization within PVC substrate with subsequent sulfonation in chlorosulfonic acid.