Flexible cationic side chains for enhancing the hydroxide ion conductivity of olefinic-type copolymer-based anion exchange membranes: An experimental and theoretical study

The performance of anion exchange membranes (AEMs) is closely related to their cationic groups, hydration degree, and nano-phase morphology. Here, mono- (and di-) quaternary ammonium, pyrrolidinium, and imidazolium cation-based AEMs were synthesized by one-step photo-polymerization. Through combination of experimental and molecular dynamics (MD) approaches, the effects of mono- (and di-) cationic functional groups on the properties of the AEMs, in terms of physicochemical, electrochemical properties, and alkaline stability were comprehensively investigated. It was concluded by the experimental data that AEMs with di-cations exhibit better water uptake, swelling ratio, alkaline stability, and higher ionic conductivity than those with mono-cations. Furthermore, mathematical models of the synthesized AEMs were established for MD simulations, and the calculated radial distribution function and mean square displacements between cationic functional groups, hydroxide ions, and water molecules obtained using the simulated molecular trajectories were examined for the solvation, transport properties, and alkaline stability of AEMs, which are in good qualitative agreement with the experimental results.