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

The investigation of proton conduction processes within artificial nanopores using phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄) not only sheds light on the mechanisms of proton conduction for these strong acids in confined environments, while also provides critical insights into the proper understanding of biological transmembrane proton transport. However, the synthesis of stable and acid-resistant host frameworks is yet a major challenges. By following that, the present study is conducted with the aim of improving the chemical stability of an imine-based COF (CPOF-10) by converting it into an amide-linked COF (CPOF-11) via a post-oxidative approach. In which, the integration of an appropriate amount of imidazole groups into the framework facilitates the efficient impregnation of liquid proton-conducting acids. The obtained results indicate the ten times greater proton conductivity of H₃PO₄@CPOF-11 than that of H₃PO₄@CPOF-10, thereby, successfully achieving 8.63 × 10^-2 S cm^-1 at 160 °C, under nitrogen (N₂) atmosphere. Moreover, the highly stable CPOF-11 tolerated H₂SO₄ doping, delivering a high proton conductivity of up to 1.70 × 10^-1 S cm^-1 at 140 °C, with a significantly low activation energy of 0.05 eV. To the best of the knowledge, this activation energy (0.05 eV) of H₂SO₄@CPOF-11 is found to be one of the lowest value among all the reported proton-conducting materials. Thus, this study will provide new understanding for the fabrication of advanced porous organic materials in fuel cells application.