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_(3)^(-)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_(3)^(-)conductivity of 105 mS cm^(-1)at 90℃ was obtained at a relatively lower ion-exchange capacity of 1.17 mmol g^(-1).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.