Covalent grafting of cobalt aminoporphyrin-based electrocatalyst onto carbon nanotubes for excellent activity in CO2 reduction

Abstract

Electrochemical reduction of carbon dioxide (CO2ERR) provides a promising method for managing global carbon balance by transforming CO2 into green chemicals. However, the development of efficient electrocatalysts for the fast and selective CO2 reduction is still a big challenge. Herein we report a study on CO2ERR electrocatalytic activity of amino-substituted Co porphyrin (CoTAP) as a function of its immobilization mode. It is demonstrated that the covalently grafted complex CoTAP-cov exhibits a turnover frequency to CO formation (TOFco) of 6.0 s−1 and the Faradic efficiency to CO (FEco) of ~100% at the overpotential of 550 mV making it one of the best catalysts to date. In contrast, noncovalently immobilized counterpart CoTAP-noncov shows a more moderate TOFco of 2.3 s−1 and lower FEco of 85%. Our results demonstrate that the presence of the donating -NH2 groups within the lateral aromatic moiety is required to maximize the activity of the complex in CO2ERR. In turn, covalent grafting both mitigates the aggregation of the porphyrin catalyst and enhances the interfacial electron delivery rate. The combination of these factors furnishes a catalyst with an excellent intrinsic TOFco as high as 36.6 s−1.