Synthesis and properties of anion exchange membranes with dense multi-cations and flexible side chains for water electrolysis

To further improve the performance of anion exchange membranes (AEMs) for water electrolysis, a class of poly (aryl ether sulfone)s with multiple quaternary ammonium cations on the side chains (PAES-MQA-x, “x” represents a functional chain segments, “MQA” represents multiple quaternary ammonium) are designed and synthesized. Their chemical and micro phase separation structures are characterized by hydrogen nuclear magnetic resonance (1H NMR) and atomic force microscope (AFM), respectively. The ion exchange capacity of PAES-MQA-x is in the range of 2.01–2.51 mmol/g. Their water uptake, swelling ratio and ionic conductivity at 80 °C are in the range of 32.7–63.2%, 12.9–18.6% and 106.23–140.85 mS/cm, respectively. The retention ratio of ionic conductivity for PAES-MQA-0.18 is up to 72.5% after immersing in 2 M NaOH solution at 80 °C for 480 h. The current density of the electrolyzer with PAES-MQA-0.18 at 2.0 V is up to 1121.5 mA/cm2 measured in 2 M NaOH solution (cathode catalyst: Pt/C; anodic catalyst: IrO2), and the electrolyzer also has good operation stability when the current density is 500 mA/cm2. Meanwhile, a comparative investigation is conducted on the relationship between the structure and properties of these membranes and some reported AEMs.