Hydroxide Ion Conduction through Viologen-Based Covalent Organic Frameworks (vCOFs): An Approach toward the...

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Alkaline fuel cells require efficient hydroxide anion (OH-) transport, which is hindered by their low diffusion rates and high mass.
• Ordered channels within covalent organic frameworks (COFs) present a potential solution for enhanced OH- conduction.

Purpose of the Study:

• To synthesize and characterize a cationic COF for efficient hydroxide ion conduction.
• To investigate the mechanism of OH- transport within the COF structure.
• To evaluate the performance of the COF in alkaline fuel cell applications.

Main Methods:

• Solvothermal-assisted Zincke reaction for vTAPA synthesis.
• Anion exchange using tertiary ammonium hydroxides to introduce OH- ions.
• Density Functional Theory (DFT) for studying anion exchange mechanisms.
• Electrochemical measurements to determine OH- ion conductivity.

Main Results:

• Synthesized vTAPA, a cationic COF with excellent stability in strong basic solutions.
• Demonstrated efficient OH- conduction via anion exchange within the COF's 1D channels.
• DFT studies confirmed favorable OH- interaction sites within the vTAPA framework.
• Butyl@vTAPA achieved a high OH- conductivity of 1.05 × 10^-4 S cm^-1 at 90 °C and 98% RH.

Conclusions:

• Cationic COFs can serve as effective platforms for directed hydroxide ion transport.
• This work presents the first direct use of COFs for hydroxide ion conduction without post-synthetic modification.
• The developed vTAPA framework offers a promising pathway for advancing alkaline fuel cell technology.