Novel Hydrophobic Covalent Cross-Linking Poly(terphenyl Isatin Piperidinium) with Poly(triphenylpyridine) for Anion Exchange Membranes

Many properties of anion exchange membranes (AEMs) exhibit trade-off effects, among which the balance between high ion conductivity and excessive swelling rate is a typical trade off problem that needs to be balanced. A hydrophobic covalent cross-linking strategy has been proposed to balance the trade-off problem. Developing a high-performance and long-term stable PTAP–PTBINP-Qx (x = 5, 10, 15, 20) AEM with a controllable cross-linking degree is achieved by combining the advantages of poly(p-terphenylpyridine) (PTAP) and poly(p-terphenyl isatin piperidium) (PTBINP-Qx) through covalent cross-linking. The dimensional stability of AEMs is improved while maintaining high ion conductivity. The PTAP–PTBINP-Q5 have good tensile strength (43.15 MPa), high hydroxide conductivity (130.38 mS/cm at 80 °C), low swelling (16.73% at 80 °C), and good alkali stability (the conductivity was retained at 83.27% in 2 M NaOH at 80 °C for 1800 h). A H2/O2 fuel cell based on the PTAP–PTBINP-Q5 AEM exhibited a maximum power density of 256 mW/cm2 at 565 mA/cm2. Covalent cross-linking is an effective method to enhance the size stability of membranes, which can enhance their mechanical properties and suppress swelling, while maintaining high ion conductivity.