Full conjugated poly(1,4-phenyldiazo porphyrin cobalt) covalent organic framework with D-π-A structure enhancing bifunctional oxygen catalytic performance

Abstract

Fully conjugated covalent organic frameworks (COFs) are widely used in electrocatalysis. The COF with –ph–NH₂ edge poly(1,4-phenyldiazo porphyrin cobalt) (A-PpazoPorCo) is synthesized by adjusting the molar ratio of the reaction material, and exhibits high delocalization energy to significantly enhance thermal stability. The nitrogen in the azo bond improves the adsorption capacity for ORR and OER catalytic intermediates, while the –ph–NH₂ group further increases the electron cloud density at the Co–N₄ center in A-PpazoPorCo. Density functional theory (DFT) calculations reveal that the strong electron-donating –ph–NH₂ groups and the electron-donating azo bonds form an electron donor-π-electron acceptor (D-π-A) structure, which further enhances the electron cloud density. The strong π-π interaction between A-PpazoPorCo and three-dimensional graphene (3D-G) significantly boosts the oxygen catalytic performance of the A-PpazoPorCo/3D-G. The catalytic ORR half-wave potential (E_1/2) of A-PpazoPorCo/3D-G can reach 0.880 V vs. RHE. The total overpotential (△E = E_j=10-E_1/2) is 0.617 V, demonstrating excellent bifunctional oxygen catalytic performance. The efficient oxygen catalytic performance indicates that A-PpazoPorCo/3D-G has the potential for application in fuel cells cathodes and overall water splitting anodes.