Novel alkaline anion exchange membranes containing pendant benzimidazolium groups for alkaline fuel cells

Novel benzimidazolium (BIm) functionalized anion exchange membranes (AEMs) are synthesized and characterized for alkaline fuel cells (AFCs). Poly(phenylene oxide) (PPO) is firstly brominated followed by nucleophilic substitution reaction with methylbenzimidazole to obtain the objective BIm-PPO AEMs. Such solution-casting AEMs show good mechanical and thermal stabilities as well as the favorable fuel cell-related indicators, including high ion exchange capacity, proper water uptake and high ionic conductivity. In addition, a single H2/O2 fuel cell test by employing the optimal BIm-PPO-0.54 AEM yields a peak power density of 13 mW cm−2 at 35 °C, indicating the potential application of BIm-PPO AEMs in AFCs. Compared with the analogous AEMs based on PPO containing the classical pendant quaternary ammonium and imidazolium cations, BIm-PPO AEMs show the advantages in dimensional, mechanical and thermal stabilities, while simultaneously exhibiting the higher ionic conductivity. Compared with polybenzimidazolium based AEMs, where BIm cations distribute within the polymer backbone, AEMs herein present the higher ionic conductivity and power density (produced from a single cell test) due to the better mobility and aggregation abilities of pendant BIm cations attached to the backbone via a side chain relative to those distribute within the polymer backbone.