Stepwise Post-Modification of Pyridine-Imine COFs for Enhanced Hydrolytic Stability and Proton Conductivity

Emerging as a type of promising material for proton conduction, covalent organic frameworks (COFs) assembled from dynamic imine bonds face a challenge of surmounting hydrolytic instability to achieve long-term performance in humid environments. In this work, we report a post-synthetic strategy to simultaneously enhance the hydrolytic stability and hydrophilicity of a pyridine-imine-based COF, COF-LIFM7, without compromising its crystallinity and porosity. A bifunctional monomer containing amino and acetal groups was employed to construct the primary framework, which was subsequently modified via amide formation and pyridine N-oxidation to yield COF-LIFM7-Amide and COF-LIFM7-Amide-N⁺O^-. These stepwise modifications increased the polarity and hydrogen-binding sites within COF pores to improve water affinity, leading to a three-order-of-magnitude enhancement in the proton conductivity for COF-LIFM7-Amide-N⁺O^-, reaching 1.9 × 10^-3 S cm^-1 at 95% relative humidity and 70 °C. This study highlights a generalizable post-synthetic approach for tuning the pore chemistry of COFs to achieve high performance in proton-conducting applications under humid conditions.