Highly stable electron-withdrawing C[dbnd]O link-free backbone with branched cationic side chain as anion exchange membrane

Abstract

To break the alkaline stability limitation of aryl-ether cleavage in anion exchange membranes (AEMs), novel electron-withdrawing CO link-free polymer backbone with spacer-tunable branched ionic side-chain is synthesized via the Leuckart-Menshutkin route. Density functional theory studies show that replacing CO links in conventional poly(aryl ether ketone)s (PAEKs) with electron-donating C–NH2 groups followed by grafting long flexible spacer cationic side chain can not only elevate the barrier height of aryl-ether cleavage by increasing electron cloud density on the ether-connected carbon atom, but also result in higher barrier height of quaternary ammonium (QA) group degradation by providing stronger steric hindrance effect and higher lowest unoccupied molecular orbital (LUMO) energy. Long pendant QAs also facilitate microphase separation and ion conduction. The PEAM-2C6 AEM with flexible hexyl-spacer branched cationic side chain achieves high ion conductivity (128.2 mS cm−1 at 80 °C), as well as excellent alkaline stability (no backbone degradation and 81% retaining of original conductivity) after immersion in 4 M KOH at 80 °C for 400 h. H2/O2 fuel cell assembled with PEAM-2C6 exhibits a maximum peak power density of 499 mW cm−2 at 80 °C. Electron-withdrawing link-free strategy provides an effective way to fabricate alkaline stabilized polyelectrolytes along with high ion conductivity.