Polynorbornene-based anion exchange membranes with hydrophobic large steric hindrance arylene substituent

To restrain excessive water uptake (WU) and swelling ratio (SR) of the quaternized polynorbornene anion exchange membrane (AEM) without sacrificing its anion conductivity, hydrophobic arylene substituent was introduced into polymer chain. The resultant cyclic olefin polymers (PBH-x-QA series) exhibited high glass-transition temperature (Tg) and tensile strength to meet the most important requirements of use as AEMs. Besides, the PBH-x-QA with ion exchange capacity (IEC) value ranged from 1.26 to 2.08 meq/g showed appropriate water uptake, good dimensional stability, and excellent tensile properties. The PBH-50%-QA exhibited water uptake of 31.0 wt% and swelling ratio (SR) of 17.6%. These values were much lower than those of PBN-26%-QA (WU = 95.5%, SR = 33.8%), which exhibited similar IEC value but had no arylene substituent. Notably, the PBH-60%-QA showed excellent hydroxide conductivity up to 101.9 mS/cm at 80 °C without excessive swelling in water, while PBH-50%-QA membrane showed excellent alkaline stability without visible loss of hydroxide conductivity, even after being immersed in 1 M NaOH aqueous solution over the 16-day test at 80 °C. A platinum-catalyzed H2/O2 fuel cell with PBH-50%-QA AEM presented a peak power density up to 228 mW cm−2 without optimized membrane electrode assembly fabrication process.