Branched Poly(Aryl Piperidinium) Membranes for Anion‐Exchange Membrane Fuel Cells

Abstract Anion‐exchange membrane fuel cells (AEMFCs) are a promising, next‐generation fuel cell technology. AEMFCs require highly conductive and robust anion‐exchange membranes (AEMs), which are challenging to develop due to the tradeoff between conductivity and water uptake. Here we report a method to prepare high‐molecular‐weight branched poly(aryl piperidinium) AEMs. We show that branching reduces water uptake, leading to improved dimensional stability. The optimized membrane, b‐PTP‐2.5, exhibits simultaneously high OH − conductivity (>145 mS cm −1 at 80 °C), high mechanical strength and dimensional stability, good processability, and excellent alkaline stability (>1500 h) in 1 M KOH at 80 °C. AEMFCs based on b‐PTP‐2.5 reached peak power densities of 2.3 W cm −2 in H 2 −O 2 and 1.3 W cm −2 in H 2 ‐air at 80 °C. The AEMFCs can run stably under a constant current of 0.2 A cm −2 over 500 h, during which the b‐PTP‐2.5 membrane remains stable.