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.