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

Area of Science:

• Materials Science
• Chemistry
• Chemical Engineering

Background:

• Covalent organic frameworks (COFs) are promising for proton conduction.
• Imine-bond-based COFs suffer from hydrolytic instability in humid environments.
• Long-term performance of COFs is limited by degradation in moist conditions.

Purpose of the Study:

• To develop a post-synthetic strategy to improve hydrolytic stability and hydrophilicity of pyridine-imine-based COFs.
• To enhance proton conductivity of COFs for applications in humid environments.
• To maintain crystallinity and porosity of COFs during modification.

Main Methods:

• Constructed a primary COF (COF-LIFM7) using a bifunctional monomer with amino and acetal groups.
• Applied post-synthetic modifications: amide formation and pyridine N-oxidation.
• Characterized the modified COFs (COF-LIFM7-Amide and COF-LIFM7-Amide-N⁺O⁻) for stability, porosity, and proton conductivity.

Main Results:

• Stepwise modifications increased pore polarity and hydrogen-binding sites, enhancing water affinity.
• Achieved a three-order-of-magnitude enhancement in proton conductivity for COF-LIFM7-Amide-N⁺O⁻.
• Proton conductivity reached 1.9 × 10⁻³ S cm⁻¹ at 95% relative humidity and 70 °C.

Conclusions:

• The developed post-synthetic approach significantly improves hydrolytic stability and proton conductivity of COFs.
• Modified COFs demonstrate high performance in proton conduction under humid conditions.
• This strategy offers a generalizable method for tuning COF properties for energy applications.