Simple Transformation of Covalent Organic Frameworks to Highly Proton-Conductive Electrolytes

We report the rational design and implementation of a new class of gel guest-assisted, ionic covalent organic framework (COF) membranes that exhibit superior H⁺ conduction. The as-synthesized COFs are postmodified via a lithiation (or sodiation) treatment. The hydrophilic Li or Na ions in the COFs form a dense and extensive hydrogen-bonding network of H₂O molecules with mobile H⁺ at the periphery, thereby transforming COFs into H⁺ conductors. Then, the ionic COFs are assembled into a flexible H⁺ conductor membrane via a gelation process, where the organic gel provides both mechanical strength and additional H⁺ carriers for fast H⁺ conduction. The final COF-based membrane exhibits an excellent H⁺ conductivity of 1.3 × 10^-1 S cm^-1 at 313 K and 98% relative humidity, which are the highest values of the COF-based H⁺ conductors reported until now and are even comparable with those of the typical commercial Nafion membrane. We anticipate that the two-in-one strategy would open up a porous COF-driven new molecular framework and membrane architectural design/opportunity for development of next-generation ionic conductors.