Polycarbazole-based anion exchange membranes containing flexible side-chain linked piperidine pendants for alkaline fuel cells

Abstract

In recent years, advancements in anion exchange membranes (AEMs) have notably enhanced the overall performance of anion exchange membrane fuel cells (AEMFCs). However, issues like limited alkali stability and low ionic conductivity of AEMs have become apparent. In this study, focusing on molecular design, a series of polycarbazole-based AEMs with flexible side chains, named PCP-n (where ‘n’ denotes the molar ratio of the newly synthesized monomer BHC in carbazole derivatives), were developed. The integration of long flexible side chains fosters chain movement and the clustering of piperidine cations, leading to distinct hydrophilic/hydrophobic nanoscale phase separation within the PCP-n membranes. Moreover, the PCP-n membranes demonstrate effective water management capabilities, with the PCP-90 membrane displaying a 32 % water uptake and an in-plane swelling ratio below 20 % at 80 °C. The introduction of an ether-free main chain based on carbazole derivatives along with the highly stable piperidine cationic group endows the PCP-n membranes with exceptional alkali resistance. Following a 1500-h immersion in 2 M KOH at 80 °C, the PCP-90 membrane successfully retains 79.92 % of its original ionic conductivity. Given its substantial thermal stability and mechanical strength, the PCP-90 membrane underwent testing in membrane electrode assembly and single-cell performance, achieving a notable peak power density of 275.64 mW cm⁻² and an open-circuit voltage of 0.98 V. Overall, the impressive comprehensive performance of the PCP-n membranes suggests a promising future for their application.