Cobalt Quaterpyridine Complexes for Highly Efficient Heterogeneous CO2 Reduction in Aqueous Media

Abstract Ligands play a critical role in the electrocatalytic CO 2 reduction reaction (CO 2 RR) based on heterogeneous molecular catalysts. Previous research on heterogeneous molecular electrocatalysis has mainly dealt with N4 ligands with pyrrole as subunits (porphyrin, phthalocyanine, etc.), while ligands constructed from pyridine subunits remain uncommon. The examples for comparing active configurations are few and far between. Herein, the development of new N4 cobalt complexes based on pyridine subunits is explored. After anchoring onto carbon nanotubes, they can exhibit CO 2 RR activity at a low overpotential of 140 mV, and high activity from ‐0.30 to ‐0.60 V versus reference hydrogen electrode with a selectivity of above 98%. Excellent performance at large current densities can also be observed in a flow cell. In situ attenuated total reflectance‐Fourier transform infrared spectroscopy proves that such electrocatalysts exhibit CO production at lower overpotential and moderate CO adsorption ability over a wide potential range. From density functional theory calculations, it is shown that a pyridine‐based cobalt complex on a carbon substrate can reduce the Gibbs free energy for reactions further than its counterpart pyrrole‐based ones. Further analysis proves that the semimetal behavior of optimized d‐orbitals may facilitate charge transfer and increase the activity. This provides a new insight for understanding catalytically active moieties in heterogeneous molecular catalysts with ligands constructed from pyridine subunits.