Hexa-Arm Branched Anion Exchange Membranes With Enhanced Conductivity and Robustness for Fuel Cells and Water Electrolyzers.

The key requirement for applying anion exchange membranes (AEMs) in water electrolyzers and fuel cells is the concurrent enhancement of hydroxide conductivity and alkaline stability. To this end, we herein report a novel hexa-arm branched poly (aryl piperidinium) AEM incorporating bulky three-dimensional tris (4-carbazol-9-ylphenyl) amine (TCA) unit. The TCA unit creates a high-density ion conduction network via increased free volume and promoted microphase separation, while its steric hindrance effect protects the piperidinium cations from hydroxide attack. With a TCA content of 3%, the fabricated membrane (ion exchange capacity being 2.75 mmol g-1) achieves an OH- conductivity of 155.7 mS cm-1 at 80°C and retains 95.1% conductivity after 2000 h in 1 M NaOH at 80°C. When assembled into a fuel cell, it delivers a peak power density of 1.95 W cm-2 at 80°C under 1.3 bar back pressure; in a water electrolyzer operating at 80°C, it yields a current density of 9.51 A cm-2 at 2.0 V. This study offers a novel branching strategy to improve ion transport in AEMs and demonstrates how the branching degree influences alkaline stability of the membrane, which is useful for further improvement of the membrane and device performances.