Novel polyaryl isatin polyelectrolytes with flexible monomers for anion exchange membrane fuel cells

Abstract

The stability of the anion exchange polyelectrolytes is closely tied to the durability of anion exchange membrane fuel cells. Given their excellent alkali resistance, ether-free polymer backbones have attracted considerable attention for use in anion-exchange polyelectrolytes. Herein, a series of side-chain-type poly(terphenylene-co-dibenzyl N-(6-bromohexyl)-isatin) copolymers (QAPTDBHI-n) were synthesized via superacid-catalyzed polymerization and a subsequent quaternization reaction. The cyclic cardo groups in the backbones enabled the formation of nanovoids, which facilitated ionic clusters’ self-aggregation. The introduction of flexible bibenzyl monomers provided the polymers with a spatially foldable structure, promoting the aggregation of ion clusters and strengthening interchain interactions. Compared with the membrane without flexible monomers, QAPTDBHI-n membranes exhibited higher hydroxide conductivity (>115 mS cm−1 at 80 °C), outstanding mechanical stability (tensile strength: 50.91–60.76 MPa, elongation at break: 14.27%–26.06%), and superior alkali resistance (1 M NaOH at 80°C for >1500 h and <9.5% OH− conductivity loss). Regarding fuel cell performance, the AEMFC based on QAPTDBHI-40 ionomer achieved a peak power density of 1.14 W cm−2 (H2–O2) and 0.86 W cm−2 (H2-Air, CO2 free) at 80 °C due to its higher water uptake, OH− conductivity, and lower phenyl concentration.