A Comparison between the Performance of Two Different Cation Groups in Anion Exchange Membranes

Two anion exchange membranes with different cations are prepared based on poly(benzimidazole imide). Regarding the similar main chain for both membranes, the performance of imidazolium cations in Q-PBII 1 and quaternary ammonium salts in Q-PBII 2 is compared by various parameters including anion conductivity, chemical stability, cell performance, and mechanical properties. Q-PBII 1 exhibits higher stiffness (in both dry and wet form) while Q-PBII 2 shows higher elongation and better flexibility (in both dry and wet form). Despite approximately similar IEC values for both membranes, Q-PBII 2 exhibits higher water uptake (71%) and anion conductivity at 80 degrees C (69 mS.cm(-1)) than Q-PBII 1. Also, Q-PBII2 shows better single-cell performance (46 mW.cm(-2) at a current density of 143.8 mA.cm(-2)). Investigation of long-time stability reveals that Q-PBII 1 is more stable than Q-PBII 2. The Q-PBII 1 shows less than 5% weight loss after 11 days while this value for Q-PBII 2 is about 28% after 11 days (in 2 M NaOH).