Azole structures influence fuel cell performance of phosphoric acid-doped poly(phenylene oxide) with azoles on side chains

We synthesized three types of polymer electrolyte membranes (PEMs) by functionalizing poly(phenylene oxide) with triazole, benzimidazole and imidazole groups, respectively on the side chains. The effect of azole structures on the fuel cell performance was investigated by analyzing and comparing the PEM properties at the sufficient PA doping level. We reveal for the first time that PEM performance is influenced by azole structures (pKa and steric hindrance). The higher pKa of imidazole was advantageous to the formation of protonic defects, enhancing the proton conduction. However, the steric hindrance of bulky benzimidazole interrupted acid-base interaction and the formation of protonic defects. The imidazole-containing membrane (XIMPPO) showed the anhydrous proton conductivity 130 mS/cm at 150 °C and the triazole-containing membrane (XTAPPO) and the benzimidazole-containing membrane (XBIPPO) showed 114 mS/cm and 102 mS/cm, respectively. Imidazole was also the most effective for the fuel cell performance, showing the peak power density of 0.20 W/cm2 and XTAPPO and XBIPPO showed 0.16 W/cm2 and 0.17 W/cm2, respectively.