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

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Abstract
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 Coɪ 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.

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