Ether-Free Polybenzimidazole Bearing Pendant Imidazolium Groups for Alkaline Anion Exchange Membrane Fuel Cells Application

A series of ether-bond free polybenzimidazole (PBI) bearing pendant imidazolium groups (HIm-PBI and PIm-PBI) are synthesized via a low cost preparation process under mild reaction conditions. HIm-PBI and PIm-PBI show excellent membrane forming property, and flexible HIm-PBI- and PIm-PBI-based membranes are prepared by casting the polymer/dimethyl sulfoxide solution. For a comparison, ether-bond free PBI without pendant imidazolium groups (I-PBI) was synthesized and characterized in detail, and I-PBI shows poor membrane forming ability under the same conditions. HIm-PBI-based anion exchange membranes (AEMs) with the longer pendant alkyl side chain exhibit larger ionic clusters than that of PIm-PBI with the shorter one. Both HIm-PBI- and PIm-PBI-based AEMs show excellent alkaline stability, and the HIm-PBI-based AEMs show a high conductivity of 63.4 mS cm–1 at 80 °C, while the value for PIm-PBI-based AEMs is 57.6 mS cm–1. The H2/O2 single-cell assembled with HIm-PBI shows a maximum power density of 444.5 mW cm–2 at 60 °C, which is higher than the one with PIm-PBI (337.5 mW cm–2). A feasible approach to the synthesis of ether-bond free PBI-based AEMs is proposed, and these results indicate that the ether-bond free PBI-based AEMs are promising materials for fuel cell applications.