Benzimidazolium functionalized polysulfone-based anion exchange membranes with improved alkaline stability

The stability of anion exchange membranes (AEMs) is an important feature of alkaline exchange membrane fuel cells (AEMFCs), which has been extensively studied. However it remains a real challenge due to the harsh working condition. Herein, we developed a novel type of polysulfone-based AEMs with three modified 1,2-dimethylbenzimidazoliums containing different substitutes at C4- and C7-position. The results showed that the introduction of the substitutes could obviously improve the dimensional and alkaline stabilities of the corresponding membranes. The swelling ratios of resultant AEMs were all lower than 10% after water immersion. The membrane with 4,7-dimethoxy-1,2-dimethylbenzimidazolium group exhibited the highest alkaline stability. Only 9.2% loss of hydroxide conductivity was observed after treating the membrane in 1 mol·L−1 KOH solution at 80 °C for 336 h. Furthermore, the density functional theory (DFT) study on the three functional group models showed that the substitutes at C4- and C7-position affected the lowest unoccupied molecular orbital (LUMO) energies of the different 1,2-dimethylbenzimidazolium groups.