Development of Imidazolium-type Anion-Exchange Membranes for Alkaline Fuel Cell Application

This study reports the development of imidazolium-type anion exchange membranes (Im-AEMs) based on the functionalization of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) using 1-methylimdazole. Aromatic polymers bearing bromomethyl, instead of chloromethyl, functional groups were employed as base materials to avoid complicated chloromethylation which require toxic reagents. H NMR and FT-IR spectroscopic data indicated the synthesis of a series of membranes with controlled ion-exchange capacities (achieved by varying the amount of 1-methylimdazole). Due to the conjugated structures of imidazolium cations, the novel Im-AEMs display enhanced short-term thermal and chemical stabilities compared with classical quaternary ammonium-type AEMs. In addition, the imidazolium salts exhibit excellent solubility in polar aprotic solvents, such as NMP and DMSO, which allowed the exploitation of a pre-functionalized strategy for the synthesis of the AEMs. As a consequence, the Im-AEMs displayed conductivities up to > 100 mS cm at 80°C, which could be attributed to the establishment of a nano-scale phase-separated morphology as directed by the solvent casting process. A H2/O2 fuel cell test yielded a peak power density of 30 mW cm at a current density of 76 mA cm; this will be improved on development of a chemical compatible imidazolium-based alkaline ionomer for use as ionic polymer binder in the electrodes’ catalyst layers.