Polynorbornene-Based Anion Exchange Ionomers with Percolated Dual-Domain Ion-Transport Channels

Anion-exchange ionomers (AEIs) serve as catalyst binders and hydroxide conductors in anion-exchange membrane fuel cells (AEMFCs), yet conventional bulk-membrane-derived AEIs often fail to meet the transport and interfacial demands of ultrathin catalyst layers. Herein, hydroxyl-rich polynorbornene-based AEIs were developed to construct coupled dual-domain OH– transport pathways. N+-rich ionic domains facilitate charge-driven ion conduction, while densely distributed hydroxyl groups establish continuous hydrogen-bonding networks to bridge nanoscale discontinuities and suppress swelling. The optimized QA-HPNB-25% achieves an OH– conductivity of 93.64 mS cm–1 at 80 °C, a low swelling ratio of 10.4%, and over 90% conductivity retention after 1000 h in 1 M KOH at 80 °C. At an ionomer-to-carbon ratio of 0.3, it balances ion transport, interfacial wetting, and gas accessibility, delivering a peak AEMFC power density of 657.91 mW cm–2. These results highlight that nanoscale ion-channel architecture and interfacial ionomer organization are critical to AEI performance in ultrathin catalyst layers.