Cationic Covalent Organic Frameworks: A Simple Platform of Anionic Exchange for Porosity Tuning and Proton Conduction

Mimicking proton conduction mechanism of Nafion to construct novel proton-conducting materials with low cost and high proton conductivity is of wide interest. Herein, we have designed and synthesized a cationic covalent organic framework with high thermal and chemical stability by combining a cationic monomer, ethidium bromide (EB) (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide), with 1,3,5-triformylphloroglucinol (TFP) in Schiff base reactions. This is the first time that the stable cationic crystalline frameworks allowed for the fabrication of a series of charged COFs (EB-COF:X, X = F, Cl, Br, I) through ion exchange processes. Exchange of the extra framework ions can finely modulate the COFs’ porosity and pore sizes at nanoscale. More importantly, by introducing PW12O40 3– into this porous cationic framework, we can greatly enhance the proton conductivity of ionic COF-based material. To the best of our knowledge, EB-COF:PW 12 shows the best proton conductivity at room temperature among ever reported porous organic materials.