Molecular modulating of cobalt phthalocyanines on amino-functionalized carbon nanotubes for enhanced electrocatalytic CO₂ conversion

Metal porphyrins and metal phthalocyanines (Pc) constitute a promising class of metal molecular catalysts (MMCs) for efficient CO₂-to-CO electrocatalytic conversion due to their well-defined molecular structures. How to adjust the local coordination and electronic environment of the metal center and enhance the molecular-level dispersion of the active components remains as great challenges for further improving the performance. Herein, a cobalt(II) Pc (CoPc)-COOH/carbon nanotube (CNT)-NH₂ hybrid catalyst was rationally designed by clicking the CoPc-COOH molecules onto the surface of CNT-NH₂ through amidation reaction. This novel hybrid catalyst exhibited the enhanced current density of 22.4 mA/cm² and CO selectivity of 91% at −0.88 V vs. reversible hydrogen electrode (RHE) in the CO₂ electroreduction, as compared with CoPc-COOH/CNT and CoPc/CNT samples. The superior activity was ascribed to the charge transfer induced by introduction of –COOH and –NH₂ functional groups to CoPc and CNT, respectively, facilitating the active centers of Co^I being generated at lower potentials, and leading to the highest turnover frequency (TOF) being obtained over the CoPc-COOH/CNT-NH₂ hybrid catalyst. The inherent directivity and saturability of covalent bonds formed via the amidation reaction ensure not only a higher density of Co active centers, but also an improved stability for CO₂ reduction reaction (CO₂RR). The present study represents an effective strategy for improving MMCs performance by molecular modulating of metal phthalocyanines on functionalized carbon substrates directed by click confinement chemistry.