Decisive\nEffect of Hydrophobic Rigid-Flexible Coupled\nSide Chains of Polycarbazoles on the Performance of Anion Exchange\nMembranes for Fuel Cells

High-performance\nanion exchange membranes (AEMs) have garnered\nincreasing attention in recent years. However, commercial progress\nof the AEM for fuel cells is still hindered by its low ionic conductivity\nand inadequate alkaline stability. In this study, we propose the incorporation\nof a hydrophobic rigid-flexible coupled side chain into a polycarbazolyl\nAEM as an innovative approach to enhance both the conductivity and\nstability. The results demonstrate that the AEMs with hydrophobic\nrigid-flexible coupled side chains exhibit superior conductivity and\nstability compared with those without (PQMC-0). For example, the ion\nexchange capacity of PQMC-10 is reduced by 11% than PQMC-0, but its\nconductivity is enhanced by 14%, dimensional change is decreased by\nalmost half, and oxidative stability is increased by more than four\ntimes. Improved conductivity of the AEMs can be attributed to the\npresence of hydrophobic rigid-flexible coupled side chains, making\nit easier for AEM to construct microphase separation to facilitate\nion transport. Furthermore, the introduction of hydrophobic side chains\nreduces water absorption of the membrane, thereby enhancing its dimensional\nstability while minimizing the intake of free radicals or hydroxide\nions present in water. Consequently, this modification significantly\nimproves the oxidative and alkaline stability as well. Finally, the\nPQMC-10 shows a maximum power density of 649 mW cm<sup>–2</sup> in a single fuel cell, which is three times bigger than that of\nPQMC-0, indicating a promising application in the field of fuel cells.