Main-Chain Cobaltocenium-Containing Ionomers for Alkaline Anion-Exchange Membranes

Cationic metallopolymers represent a new class of ionomers as anion-exchange membranes (AEMs) for transporting hydroxide ions in alkaline fuel cells. In this work, main-chain cobaltocenium-containing polymers with a complete hydrocarbon framework were synthesized by ring-opening metathesis polymerization (ROMP) of cobaltocenium-fused cycloalkenes and cis-cyclooctene followed by backbone hydrogenation. These copolymers with varied fractions of cobaltocenium exhibit high chemical and thermal stability, low swelling, and favorable mechanical properties, with hydroxide conductivity as high as 95 mS/cm and about 94% retention of the conductivity after 45 days of exposure to high alkaline conditions. Comparison with side-chain cobaltocenium polymer-based AEMs reveals that the main-chain hydrocarbon-based polymers endow lower water uptake and swelling ratio while maintaining similar ion exchange capacity and hydroxide conductivity.