Constructing ionic channels in anion exchange membrane via a Zn2+ soft template: Experiment and molecular dynamics simulation

Abstract An effective soft-template strategy using Zn2+ metal ions is proposed to construct well-ordered ionic conductive channels in the imidazolium (Im+) functionalized polysulfone anion exchange membranes (AEMs). The divalent Zn2+ ion possesses strong electrostatic interactions to induce better microphase separation. The further removal of the sub-nanoscale water-soluble Zn2+ ions introduces free volumes to connect ionic pathways, meanwhile promotes the secondary aggregation of Im+ groups. Experiment and simulation show that Zn2+ ions organize into Zn2+ self-aggregations and interact with Im+ groups via an electrostatic anion-bridged configuration in the Zn2+ incorporated membranes, and the subsequent Zn2+ removal increases the free volume and induces the rearrangement of Im+ groups to form bigger ionic clusters (up to 7.7 nm) than those in the pristine membrane. By optimizing Zn2+ content, the induced ionic conductive channels are tailored, yielding a 50% improvement of hydroxide conductivity and achieving the top level in the previously reported polysufone-based main-chain-type AEMs. This study suggests a novel and scalable route for regulating micro-phase separations in AEMs and provides theoretical exploration for selecting effective template molecules.