Alkaline stable piperidinium-based biphenyl polymer for anion exchange membranes

Long-term alkaline stability of the anion exchange membrane is a critical requirement for its practical application under a high pH operation environment. It is an effective strategy to improve the alkaline stability of the membrane from the three aspects of the polymer backbone, cationic groups, and linkage structure. A type of alkaline stable piperidinium-based biphenyl polymer (PBP-PIP) was prepared via super electrophilic activated reaction. The all carbon-bond backbone was chosen to ensure the alkaline stability of the polymer backbone by preventing it from reacting with hydroxide. Based on the stable polymer backbone, the piperidinium group with a ring structure and β‑hydrogen-free linkage structure was considered to improve the alkaline stability of cationic groups and linkage structure by slowing down the occurrence of nucleophilic substitution and Hofmann elimination reaction. The PBP-PIP membrane exhibited hydroxide conductivity of 57 mS cm−1 at 80 °C and tensile strength of 28.2 MPa. Meanwhile, the PBP-PIP membrane showed good alkaline stability with a 76% retention of conductivity and 77% retention of tensile strength after being immersed in a 1 M NaOH aqueous solution at 80 °C for 750 h.