Polyethyleneimine functionalized covalent organic frameworks for efficient proton conduction†

Abstract

Covalent organic frameworks (COFs) have gained significant research attention as promising proton conducting materials due to their prominent properties such as remarkable specific surface area, regular structure and minimal density. Herein, a series of polyethyleneimine (PEI) functionalized COFs (TpPa–SO₃H@PEI-wt%) with high amino density were designed and synthesized to promote the proton hopping in COF hexagonal nanopores, where flexible polyethyleneimine (PEI) has strong proton capture and release capabilities, which can improve the continuity of the hydrogen-bonding networks and provide a low energy barrier pathway for proton hopping in the system, and thus improving proton transfer efficiency. Importantly, the proton conductivity can be well modulated by varying the molecular weight and grafted amount of PEI, among which, TpPa–SO₃H@PEI₆₀₀-40% exhibited a remarkable proton conductivity as high as 5.9 × 10⁻³ S cm⁻¹ along with a low activation energy of 0.14 eV at 98% RH and 80 °C, thanks to the Grotthuss mechanism for proton conduction. In addition, TpPa–SO₃H@PEI₆₀₀-40% showed excellent stability in the water vapor environment and no obvious conductivity decrease was observed even after 72 hours of continuous conductivity measurements. This demonstrates its good potential for the development and application of high proton conductive materials.