(Invited) Novel Ionomers and Ionomer Membranes for Fuel Cells and Redox-Flow Batteries

Abstract

In this contribution the development of new nonfluorinated and partially fluorinated polymeric platsforms containing perfluoroaromatic building blocks, and their modification with phosphonic and/or sulfonic acid groups and/or anion-exchange groups and/or flexible alkane side chains by nucleophilic aromatic substitution of F or via other synthesis routes is described. The prepared polymers were, where appropriate, blended among each other or with basic high-performance commercial polymers such as polybenzimidazoles or self-synthesized novel basic aromatic polymers to further improve their membrane properties by ionic cross-linking. Moreover, composite membranes consisting of ion-conductive or non-conductive electrospun fiber mats which were filled with PFSA dispersions were synthesized and optimized. The synthesized ionomers and ionomer (blend) membranes were characterized in terms of composition via NMR and FTIR, molecular weight by size exclusion chromatography (SEC), thermal stability via TGA-FTIR-GC-MS coupling and via DSC, and mechanical properties via stress-strain tests and DMA, morphology via electron microscopy, and conductivity via impedance spectroscopy. The (blend) membranes were then applied in fuel cells (low-T and high-T, H2 and direct alcohol fuel cells), and in redox-flow batteries, yielding good performance in these applications.