Structural Regulation of Coupled Phthalocyanine-Porphyrin Covalent Organic Frameworks to Highly Active and Selective Electrocatalytic CO Reduction.

Covalent organic frameworks (COFs) have been applied as potential electrocatalysts for CO reduction reaction (CO 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-2H Por) or Type 1:1 (CoPc-H Por) COFs. Electrocatalytic CO 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-2H Por) delivers lower overpotential, higher current density, and CO selectivity than Type 1:1 COF (CoPc-H Por) and CoPc monomer. Theoretical and experimental results reveal that the better CO RR activity of CoPc-2H Por than CoPc-H Por can be attributed to its larger pore size and conjugate structure, which then cause more efficient electron transfer, adsorption/activation of CO , faster mass transfer, and reaction kinetics. This work provides a new idea in the structural design of COF-based electrocatalyst for efficient CO RR.