Cobalt Phthalocyanine-Based Covalent Organic Framework with Bimetallic Synergistic Effect for Efficient Photocatalytic CO2 Reduction

Abstract

Covalent organic frameworks (COFs) have emerged as promising photocatalysts for the CO₂ reduction reaction (CO₂RR). Among various building components, metal phthalocyanines have gained significant attention owing to their excellent photochemical properties and well-defined M–N₄ sites. Herein, tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine cobalt(II) (CoTAPc) are used as connection points to couple with bipyridine (bpy) for constructing an imine linked CoPc-bpy COF and then coordinated with Re(CO)₃Cl to create a novel CoPc-Rebpy COF. It is found that there exists an intramolecular charge transfer from the CoPc to Rebpy units and then to Re center for CO₂RR via Z-scheme molecular heterojunction mechanism. Under visible light illumination, the CoPc-bpy and CoPc-Rebpy COFs deliver CO yields of 3068 and 6680 μmol g^–1 h^–1, respectively. The significantly increased activity of CoPc-Rebpy COF can be ascribed to the synergistic effect of Re catalytic sites and the electron capture center provided by the CoPc unit. These findings present an effective strategy for COF-based photocatalysts for CO₂RR.