Composite anion-exchange-membranes: Construction of percolated structures and exponential improvement of ionic conductivity

In composite anion exchange membranes (AEMs) of PVDF-co-(PVDF-g-IL) [polyvinylidene fluoride-copolyvinylidene fluoride grafted with ionic liquid], micro -phase separation takes place, producing PVDF and PVDF-g-IL phases. The evolution from isolated to percolated structures of ion-containing phase has been tracked by increasing weight fraction of PVDF-g-IL in copolymer. Relative to the reference (islands of ion-containing phase), the percolated structures exhibit improved connectivity among conducting phases and facilitate the formation of continuous ion transfer channels, contributing to an exponential improvement in ionic conductivity (up to 3-4 orders of magnitude) which has been validated with the help of water uptake, swelling ratio and mechanical performances of resultant AEMs. Our results not only achieve substantial leap of ionic conductivity in the case of low ion exchange capacity (IEC), but also provide direct evidence for the relationship between microphase separated structures and ionic conductivity.