Two new anion exchange membranes based on poly(bis-arylimidazolium) ionenes blend polybenzimidazole

The development of polymer membranes with excellent alkaline stability and high hydroxide conductivity is a huge challenge to fuel cells. Herein, two blend membranes based on poly(bis-arylimidazolium)s (i.e. Ppbim and Ptpim) and polybenzimidazole (PBI) are prepared and used as anion exchange membranes. Ppbim and Ptpim ionenes are synthesized from bis-imidazole compounds (i.e. pbim and tpim) and α,α′-dibromo-p-xylene via the Menshutkin reaction, while pbim and tpim are synthesized from 2-phenylbenzimidazole (or 2,4,5-triphenylimidazole) with 1,4-dibromobutane through the nucleophilic substitution reaction. The physicochemical properties such as water uptake, ion exchange capacity, swelling, tensile strength and conductivity can be adjusted by changing the molar ratio of pbim (or tpim) to PBI in the blend membranes. Comparing with Ppbim, Ptpim containing bulky tri-phenyl groups exhibits better alkaline stability due to the steric hindrance effect of tri-phenyl groups. The technical feasibility of the Ptpim-51%PBI membrane for the anion exchange membrane fuel cell is demonstrated by the polarization curves. This work provides a straightforward method to synthesize water-insoluble ether-free polymers with dicationic groups in the polymer repeat unit.