Anion Exchange Membranes (AEMs) with Perfluorinated and Polysulfone Backbones with Different Cation Chemistries

Abstract

Perfluorinated (PF) and polysulfone (PSF) backbones have been functionalized with multiple cation chemistries with varying basicities to prepare anion exchange membranes. The different cation and polymer backbone chemistries were evaluated to ascertain their influence on cation stability in alkaline environments, ionic conductivity, water uptake, and fuel cell performance. Evidence from the several cations/backbones studied support the following conclusions: i.) Basicity of the cation is an appropriate heuristic for assessing ionic conductivity, but it is not always appropriate for comparing alkaline stability across cations with different inorganic atoms. ii.) Phosphonium cations with similar or greater basicity than ammonium cations are observed to have less water uptake, but degrade more rapidly since they favor the formation of ylides. iii.) PF backbones with a sulfonyl group adjacent to the cation site exhibit a higher rate of cation site degradation in comparison to PSF backbones that have a benzyl group adjacent to the cation.