Skeleton Regulation of Covalent-Organic Frameworks From 2D to 3D Networks for High Anhydrous Proton Conduction

Developing new materials for anhydrous proton conduction under high-temperature conditions is very challenging but significant for proton exchange membrane fuel cells. Herein, a series of highly crystalline and robust covalent-organic frameworks (COFs) with different skeletons (2D and 3D) is designed and synthesized using steric hindrance engineering of the monomer. Moreover, a [4 + 2] construction approach is used to construct 3D COFs with entangled networks, which can be further post-modified with phosphite acid groups to improve intrinsic proton conduction. After loading with imidazole, COFs can realize a proton conductivity of 1.06 × 10^-2 S cm^-1 under anhydrous conditions, among the best proton-conducting COF materials loading imidazole. These materials show high stability at loading and testing conditions and maintain high proton conductivity over a wide temperature range (100-160 °C). This work provides a skeleton regulation approach to design materials for anhydrous proton conduction, showing great potential as high-temperature proton exchange membranes.