Solid-state synthesis of intrinsically proton-conducting covalent organic framework membrane

Ionic covalent organic framework (iCOF) membranes are attractive for a myriad of applications. Here, we report a mechanochemistry-based solid-state synthesis method to fabricate iCOF membranes with simplicity, scalability and sustainability. Time-dependent experiments reveal that the iCOF membrane formation process includes the structural transformation from disorder to order and the morphology change to the dense structure formed by the restacking of nanosheet-like crystallites simultaneously. The obtained free-standing iCOF membranes demonstrate high ion exchange capacity, mechanical strength and comparable proton conductivity, benefiting from the rigid crystalline framework structure and one-dimensional channels decorated with abundant proton-conducting sites. This work paves the way for synthesis of iCOF membranes in a simple and environmentally friendly manner.