Ion Conduction in Polyelectrolyte Covalent Organic Frameworks

Covalent organic frameworks (COFs) with ordered one-dimensional channels could offer a predesigned pathway for ion motion. However, implanting salts into bare channels of COFs gives rise to a limited ion conductivity. Here, we report the first example of polyelectrolyte COFs by integrating flexible oligo(ethylene oxide) chains onto the pore walls. Upon complexation with lithium ions, the oligo(ethylene oxide) chains form a polyelectrolyte interface in the nanochannels and offer a pathway for lithium ion transport. As a result, the ion conductivity was enhanced by more than 3 orders of magnitude compared to that of ions across the bare nanochannels. The polyelectrolyte COFs promoted ion motion via a vehicle mechanism and exhibited enhanced cycle and thermal stabilities. These results suggest that the strategy for engineering a polyelectrolyte interface in the 1D nanochannels of COFs could open a new way to solid-state ion conductors.