Fast Bulky Anion Conduction Enabled by Free Shuttling Phosphonium Cations.

Highly conductive anion-exchange membranes (AEMs) are desirable for applications in various energy storage and conversion technologies. However, conventional AEMs with bulky HCO or Br as counterion generally exhibit low conductivity because the covalent bonding restrains the tethered cationic group's mobility and rotation. Here, we report an alternative polyrotaxane AEM with nontethered and free-shuttling phosphonium cation. As proved by temperature-dependent NMR, solid-state NMR, and molecular dynamics simulation, the phosphonium cation possesses a thermally trigged shuttling behavior, broader extension range, and greater mobility, thus accelerating the diffusion conduction of bulky anions. Owing to this striking feature, high HCO conductivity of 105 mS cm at 90°C was obtained at a relatively lower ion-exchange capacity of 1.17 mmol g. This study provides a new concept for developing highly conductive anion-exchange membranes and will catalyze the exploration of new applications for polyrotaxanes in ion conduction processes.