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

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 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.