Imidazolium-Based Grafted Anion Exchange Membranes: Interplay between the Morphology and Anion Transport Behavior

In this report, the anion transport behavior of imidazolium-based graft-type anion exchange membranes (AEMs) having imidazolium (Im)/styrene (St) graft-copolymers was studied. We have reported the graft-copolymers coordinately form ion channels where dissociated ions are dispersed and the connectivity of channels increases with the increasing hydration number, λ (the number of water molecules per Im group). Here, we investigated the conductivity, water uptake, and anion diffusivity of AEMs with different grafting degrees (GDs) and different counterions as a function of λ. The plot of the ratio of the anion diffusion coefficient in AEMs to its diffusivity in the dilute solution (D/D0) with λ shows a superimposed master curve. This result strongly evidences that these AEMs have similar morphology relating to the anion transport, regardless of GDs and anion species. The findings in this study provide a guideline for future AEM design to enhance the ion transport efficiency.