Hydroxide Anion Transport in Covalent Organic Frameworks

Abstract

Hydroxide anion transport is essential for alkaline fuel cells, but hydroxide anion has an inherently low conductivity owing to its small diffusion coefficient and high mass. Ordered open channels found in covalent organic frameworks are promising as pathways to enable hydroxide anion transport, but this remains to be explored. Here we report designed synthesis of anionic covalent organic frameworks that promote hydroxide anion transport across the one-dimensional channels. Engineering cationic chains with imidazolium termini onto the pore walls self-assembles a supramolecular interface of single-file hydroxide anion chains in the channels. The frameworks facilitate hydroxide anion transport to achieve an exceptional conductivity of 1.53 × 10–2 S cm–1 at 80 °C, which is 2–6 orders of magnitude higher than those of linear polymers and other porous frameworks. Impedance spectroscopy at different temperatures and studies on deuterated samples reveal that hydroxide anions transport via a proton-exchange hopping mechanism. These results open a way to design framework materials for energy conversions via engineering an anionic interface.