Quaternized polybenzimidazoles with imidazolium cation moieties for anion exchange membrane fuel cells

A new series of quaternized polybenzimidazoles (PBIs) having imidazolium moieties in the main-chain and/or in the side group were synthesized for use as anion exchange membrane (AEM) for fuel cells. The polymer structures were characterized by 1H NMR, FTIR, and EDX analyses. The degree of imidazolium functionalization (DIF) of the quaternized PBI was also determined. The properties required for AEM, such as ion exchange capacity (IEC), water uptake, swelling ratio, hydrated number, and ionic conductivity were measured. The IECs of the quaternized PBIs were in the range of 0.96–1.49 mmol/g. The highest ionic conductivity of 2.72×10−2 S/cm was achieved at 80 °C. Besides, the thermal stability, mechanical properties, and alkaline stability of the quaternized PBI membranes were investigated. The results revealed that the thermal stability and mechanical properties of the membranes were acceptable, but the alkaline stability of the imidazolium moieties needs to be improved.