Redox-responsive ionic covalent organic framework films for hydroxide ion transport and tunable mechanical properties

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Hydroxide ion conduction is critical for developing advanced energy conversion and storage systems.
• Existing materials often lack the required flexibility, mechanical robustness, or stability for demanding electrochemical applications.

Purpose of the Study:

• To synthesize and characterize a novel flexible, mechanically robust viologen-based two-dimensional ionic covalent organic framework (iCOF) film.
• To evaluate the hydroxide ion conductivity, alkaline stability, and mechanical properties of the synthesized iCOF film.
• To explore the potential of redox-active units within the iCOF for multifunctional applications.

Main Methods:

• Green, catalyst-free sol-gel synthesis under ambient conditions.
• Characterization of the iCOF film's structure, mechanical properties (Young's modulus), and alkaline stability.
• Measurement of hydroxide ion conductivity at elevated temperatures.

Main Results:

• Successful synthesis of a flexible and mechanically robust viologen-based iCOF film (TG-V²⁺).
• Achieved a hydroxide ion conductivity of 9 × 10^-3 S cm^-1 at 100 °C with strong alkaline stability.
• Demonstrated a four-fold enhancement in mechanical stiffness (Young's modulus = 4.5 GPa) due to redox-active viologen units, enabling electrochromic switching.

Conclusions:

• The TG-V²⁺ iCOF film presents a promising platform for multifunctional ionic membranes.
• The combined ion-conducting and redox-responsive properties open avenues for advanced electrochemical applications.
• This work provides a proof-of-concept for designing novel iCOFs for energy storage and conversion technologies.