Decisive Effect of Hydrophobic Rigid-Flexible Coupled Side Chains of Polycarbazoles on the Performance of Anion Exchange Membranes for Fuel Cells

Abstract

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