Structural Regulation of Coupled Phthalocyanine–Porphyrin Covalent Organic Frameworks to Highly Active and Selective Electrocatalytic CO2 Reduction

Covalent organic frameworks (COFs) have been applied as potential electrocatalysts for CO₂ reduction reaction (CO₂ RR) due to their adjustable architecture and porous feature. Herein, tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine cobalt(II) (CoTAPc) are used as nodes to couple with 5,15-di(4-aminophenyl)-10,20-diphenylporphyrin (DAPor) or 5,15,10,20-tetrayl(4-aminophenyl)porphyrin (TAPor) via imidization reaction to fabricate novel coupled phthalocyanine-porphyrin Type 1:2 (CoPc-2H₂ Por) or Type 1:1 (CoPc-H₂ Por) COFs. Electrocatalytic CO₂ RR experiments show that both Type 1:2 and Type 1:1 COFs exhibit the maximum Faraday efficiency over 90% with high stability, while the Type 1:2 COF (CoPc-2H₂ Por) delivers lower overpotential, higher current density, and CO selectivity than Type 1:1 COF (CoPc-H₂ Por) and CoPc monomer. Theoretical and experimental results reveal that the better CO₂ RR activity of CoPc-2H₂ Por than CoPc-H₂ Por can be attributed to its larger pore size and conjugate structure, which then cause more efficient electron transfer, adsorption/activation of CO₂ , faster mass transfer, and reaction kinetics. This work provides a new idea in the structural design of COF-based electrocatalyst for efficient CO₂ RR.