Journal of Membrane Science | 2019
Thermally crosslinked sulfonated polybenzimidazole membranes and their performance in high temperature polymer electrolyte fuel cells
Abstract
Abstract The degradation pathway of phosphoric acid doped polybenzimidazole membranes in high temperature polymer electrolyte membrane fuel cells depends on the acid contents. If it is high, creep is discussed as the main reason. If it is low (membranes prepared by solvent evaporation and post-doping), the main cause may be loss of acid due to evaporation, in addition to a process observed at high current densities, at which a net transport of acid to the anode side is observed, which should lead to local softening of the membrane. A common way to stabilize membranes is crosslinking. Here we show that sulfonated para -polybenzimidazole membranes can be stabilized by curing at 350\u202f°C. In contrast to meta -polybenzimidazole and sulfonated para -polybenzimidazole, crosslinked sulfonated para -polybenzimidazole is insoluble in dimethylacetamide at room temperature and phosphoric acid at 160\u202f°C. At 160\u202f°C and 5% relative humidity the conductivity of crosslinked sulfonated para -polybenzimidazole and meta -polybenzimidazole are 214\u202fmS\u202fcm −1 and 147\u202fmS\u202fcm −1 , respectively. At 600\u202fmA/cm 2 , the voltage decay rate is 16\u202fμV/h, much lower than published for commercial meta -polybenzimidazole (308\u202fμV/h). Furthermore, the average voltage at 600\u202fmA/cm 2 is 523\u202fmV, while a previously published cured meta -polybenzimidazole membrane only reaches 475\u202fmV.