High-conductivity and alkaline-stable anion exchange membranes based on branched Poly(fluorene-co-aryl piperidinium) for water electrolyzers

The development of anion exchange membranes (AEMs) that simultaneously exhibit high ionic conductivity, robust mechanical strength, and excellent alkaline stability remains a critical challenge for the advancement of anion exchange membrane water electrolysis (AEMWE). Herein, we report a series of poly (fluorene-co-aryl piperidinium) AEMs (QPFCP-x-y), incorporating 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) as a branching agent and 9,9-dimethylfluorene (FLN) as a rigid co-monomer. The unique structural features of CBP direct polymer chain extension in multiple dimensions, reduce chain packing, and enhance mechanical toughness. Concurrently, the rigid FLN units effectively promote microphase separation, facilitating the aggregation of hydrophilic piperidinium groups and promoting the formation of well-defined microphase-separated ion-conducting channels. The optimized membrane achieves a high hydroxide conductivity of 161.32 mS cm −1  at 80 °C, representing an approximately 18% improvement over its FLN-free counterpart. Furthermore, the membrane demonstrates outstanding alkaline stability, retaining 86.48% of its initial conductivity after 1500 h of immersion in 3 M KOH at 80 °C. An AEMWE single cell employing the QPFCP-3-10 membrane delivers a high current density of 1.83 A cm −2 at 2.2 V in 1 M KOH at 60 °C, outperforming a commercial FAA-3-50 membrane.