Dense Hydrophobic Side Chains Enabling Poly(carbazole-isatin)-Based Anion Exchange Membranes with Both High Ionic Conductivity and Alkaline Stability

This study aims to develop an advanced anion exchange membrane that combines high ionic conductivity with long-term durability to facilitate the commercialization of fuel cells. A carbazole-isatin copolymer was designed and employed as the backbone to create a stable matrix. By adjusting the content of hydrophilic groups and incorporating densely packed hydrophobic side chains, the multidimensional properties of the membrane were systematically optimized. The membrane with high-density hydrophobic side chains showed a clear, ordered microphase-separated structure. Even with a relatively low ion exchange capacity of merely 1.43 mmol g–1, it still exhibited a hydroxide ion conductivity of 141.63 mS·cm–1 at 80 °C. Following accelerated aging testing in 2 M NaOH at 80 °C for 1608 h, the membrane retained 90.8% of its initial conductivity, indicating excellent resistance to alkaline degradation. When evaluated in H2/O2 single-cell tests at 60% relative humidity, the membrane achieved a peak power density of 557.25 mW·cm–2. Furthermore, during 80 h continuous operation at a constant current density of 100 mA·cm–2, the voltage decay rate remained minimal at only 0.545 mV·h–1, demonstrating excellent operational stability and promising potential for practical fuel cell application.