Towards high water retention of proton exchange membranes at elevated temperature via hollow nanospheres

The proton conductivity of perfluorosulfonic polymers, such as Nafion®, increases with increasing relative humidity and decreases enormously after 80 °C at the standard atmosphere due to the dehydration of the membranes. In present study, a new strategy to prepare the proton conducting membrane with higher water retaining capacity via the composite of perfluorosulfonic polymer and the hollow nanosphere of sulfonated polystyrene (sPS) is proposed. The hydrophilic and hollow nanospheres of sPS were prepared via the template polymerization. Thermogravimetric analysis (TGA) results show that the hollow sPS nanospheres exhibit an additional weight loss peak of dehydration at 136 °C besides that at 80 °C. Compared to 85–90 °C of the normal hydrated Nafion® membranes without nanospheres, the maximum temperature for dehydration in proton exchange membranes (PEMs) based on the composite of perfluorosulfonic polymer and hydrophilic hollow nanospheres is 30 °C higher. The hollow nanosphere with a nano-hole on the shell, in which the nano-hole may be formed during the etching of the template, behaves like a reservoir and provides necessary water above 100 °C as the boiling point of the water through the nano-hole is higher than 100 °C. The dehydration of the hollow nanosphere is significantly more difficult than that of the hollow sphere with micron-scale.