Novel imidazolium-functionalized anion-exchange polymer PBI blend membranes

Abstract

The potential application of anion-exchange membranes (AEMs) in alkaline fuel cells has recently experienced renewed attention as an alternative to the cation-exchange membranes used in proton exchange fuel cell (PEMFC). To date, no commercial AEM is available that is chemically, mechanically and thermally stable while maintaining high conductivities. In order to further improve the chemical stability of the blended membranes developed within our research group, the addition of both imidazoles as quaternizing agents, as well as a polymeric sulfonic component to introduce ionic cross-links between blend components was investigated. For this purpose 1-methylimidazole (MIm) and 1-ethyl-2-methylimidazole (EMIm) were selected as quaternizing agents while sulfonated polyethersulfone (SAC) was added to further improve the chemical stability of the synthesized AEMs by formation of electrostatic interactions between the AEM and the SAC blend component. The novel AEMs were evaluated in terms of properties such as ion exchange capacity (IEC), ion conductivity, weight loss with extraction experiments, water uptake and thermal stability (TGA) with the main focus on monitoring the alkaline stability. The synthesized AEMs proved chemically much more stable than the benchmark Tokuyama A201 membrane, while the acid–base imidazolium-functionalized membranes׳ conductivities also exceeded those reported for Tokuyama at temperatures below 60 °C while being comparable at temperatures from 60 °C to 80 °C