Tunable multi-cations-crosslinked poly(arylene piperidinium)-based alkaline membranes with high ion conductivity and durability

A practical polyelectrolyte system to improve the ion conductivity and lifetime of anion exchange membranes (AEMs) is a critical requirement for alkaline membrane fuel cells (AMFCs). Crosslinking is an effective approach to optimize the performance of AEMs. However, ordinary crosslinkers with a hydrophobic structure always make AEMs mechanically brittle. Herein, in response to the requirement of high-performance AEMs, a series of tunable multi-cation-crosslinked poly(biphenyl piperidinium) (PBP-xQ4) membranes were designed and prepared by embedding flexible cationic crosslinkers. The number of alkyl spacers between the cationic groups in the flexible crosslinkers were optimized to 5 and 6 to achieve optimum performance. These PBP-xQ4 membranes simultaneously have high ion conductivity (155 mS/cm at 80 °C) and good dimensional stability, and these membranes can be folded into many shapes. Besides, the crosslinking also promotes the alkaline stability of these membranes in 2 M NaOH at 80 °C: only a slight degradation is detected by 1HNMR after alkaline treatment for1800 h. All these impressive results in ion conductivity and durability are attributed to clear nanophase separation in PBP-xQ4 membranes. Moreover, the PBP-xQ4 membrane realizes a maximum power density of 234 mW/cm2 at 80 °C.