Non-pyrolysis prepared naphthalene diimide-based bimetallic phthalocyanine covalent organic polymers@carbon nanotube nanocomposites for oxygen reduction

Abstract

Covalent organic polymers (COPs) are considered promising non-precious metal catalysts for ORRs. However, as bulk COP powder generally suffers from poor electrical conductivity, heat treatment is frequently performed after the reaction, which inevitably destroys their originally designed regular structure, making their active sites complex and uncontrollable. Herein, we successfully prepared a novel naphthalene diimide-based bimetallic phthalocyanine covalent organic polymers@carbon nanotube nanocomposite electrocatalyst (CoFe/NDI-COP@CNT) via a simple solvothermal method. The non-pyrolytic preparation method greatly preserves the ordered structure of the COP framework and the well-defined active sites (CoN₄ and FeN₄). Moreover, incorporating an electron-poor NDI component into the target grid skeletons can increase the hybrid catalyst's ability to accept electrons from oxygen and further increase the density of active sites. Under the alkaline condition of 0.1 M KOH, CoFe/NDI-COP@CNTs exhibit efficient ORR catalytic activity and stability, with a half-wave potential of 0.902 V and a limiting current density of 5.362 mA cm⁻², which is superior to that of 20% Pt/C. In addition, CoFe/NDI-COP@CNTs show exceptional methanol resistance and electrochemical stability. This work provides new insights for the non-pyrolysis preparation of metal-doped carbon electrocatalysts with well-defined active sites from COPs.