Charge Separation by Imidazole and Sulfonic Acid-Functionalized Covalent Organic Frameworks for Enhanced Proton Conductivity

Abstract

The ion aggregation induced by a strong Coulomb force leads to hard charge separation and poor proton conductivity. Herein, covalent organic frameworks (COFs) linking both positive charged imidazole and negative charged sulfonic acid were produced and were finally incorporated with NH4Br molecules. As a result, the charge separation ability of NH4Br molecules is profoundly enhanced by charged groups on COFs, which is proved by X-ray photoelectron spectroscopy measurement. The proton conductivity of charged COFs is higher than that of neutral COFs, which can be as high as 3.7 × 10–3 S cm–1 at 90 °C and 100% relative humidity. The activation energy is also lower in charged COFs, demonstrating strengthened charge separation ability and easier moving proton carriers as well.