Branched Poly(aryl piperidinium) Anion Exchange Membranes with Microphase Separation for Fuel Cells

The practical application of anion exchange membranes (AEMs) in alkaline fuel cells is often constrained by a trade-off between dimensional stability and ionic conductivity. To address this challenge, we drew inspiration from the nutrient transport system of Victoria lily and mimicked its hierarchical transport architecture. By introducing a microphase-separated morphology into the membrane, we established an efficient ion transport network that facilitates rapid hydroxide (OH^–) conduction. A novel hydrophilic–hydrophobic block copolymer incorporating the branched monomer 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) was synthesized to fabricate advanced AEMs. The integration of robust CBP units not only enhanced the membrane’s dimensional stability but also altered polymer chain packing, thereby enlarging the ion-conducting channels. As a result, the membrane exhibited a high ionic conductivity (up to 179.9 mS cm^–1 at 80 °C) and excellent dimensional stability (swelling ratio of 24.4%). Furthermore, it demonstrated outstanding chemical stability, retaining over 90% of its conductivity after 1500 h in 5 M NaOH at 80 °C. To demonstrate practical applicability, the AEM was integrated into membrane-electrode assemblies (MEAs), and fuel cell performance was evaluated. The results showed excellent and stable output, achieving a peak power density of 947 mW cm^–2.