High Proton Conductivity of Acid Impregnated COFs Stabilized by Post-Oxidation

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Proton conduction in nanopores is crucial for understanding biological transport and developing artificial systems.
• Synthesizing stable, acid-resistant frameworks for strong acids like phosphoric acid (H3PO4) and sulfuric acid (H2SO4) remains a challenge.
• Existing imine-based covalent organic frameworks (COFs) may lack the necessary chemical stability for efficient proton conduction applications.

Purpose of the Study:

• To improve the chemical stability of imine-based COFs for enhanced proton conduction.
• To investigate the proton conductivity of phosphoric acid and sulfuric acid within a modified COF structure.
• To explore the potential of these materials in fuel cell applications.

Main Methods:

• Post-oxidative conversion of an imine-based COF (CPOF-10) into an amide-linked COF (CPOF-11).
• Integration of imidazole groups into the CPOF-11 framework to facilitate acid impregnation.
• Measurement of proton conductivity of phosphoric acid and sulfuric acid doped CPOF-11 at various temperatures.

Main Results:

• The amide-linked CPOF-11 exhibited ten times greater proton conductivity with phosphoric acid compared to CPOF-10, reaching 8.63 × 10⁻² S cm⁻¹ at 160 °C.
• CPOF-11 demonstrated excellent stability with sulfuric acid doping, achieving a high proton conductivity of 1.70 × 10⁻¹ S cm⁻¹ at 140 °C.
• The H₂SO₄@CPOF-11 system displayed a remarkably low activation energy of 0.05 eV, among the lowest reported for proton-conducting materials.

Conclusions:

• The post-oxidative synthesis of amide-linked CPOF-11 significantly enhances chemical stability and proton conductivity.
• The imidazole-functionalized CPOF-11 is a promising host for liquid proton conductors, offering superior performance in fuel cell relevant conditions.
• This study provides valuable insights for designing advanced porous organic materials for efficient energy conversion technologies.