Polyethyleneimine functionalized covalent organic framework for efficient proton conduction

Covalent organic frameworks (COFs) have gained significant research attention as promising proton conducting materials due to the prominent properties such as remarkable specific surface area, regular structure and minimal density. Herein, a series of polyethyleneimine (PEI) functionalized COF (TpPa-SO3H@PEI-wt%) with high amino density were designed and synthesized to promote the proton hopping in COF hexagonal nanopores, where the flexibile polyethyleneimine (PEI) has a strong proton capture and release capability, 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 of as high as 5.9×10-3 S cm-1 along with low activation energy of 0.14 eV at 98% RH and 80 °C thanks to Grotthuss mechanism for proton conduction. In addition, TpPa-SO3H@PEI600-40% showed excellent stability in water vapor environment and no obvious conductivity decrease was observed even after 72 hours of continuous conductivity measurements. This demonstrates good potential in the development and application of high proton conductive materials.