Cobalt Quaterpyridine Complexes for Highly Efficient Heterogeneous CO_2 Reduction in Aqueous Media

摘要

Ligands play a critical role in the electrocatalytic CO_2 reduction reaction(CO_2RR) based on heterogeneous molecular catalysts. Previous research onheterogeneous molecular electrocatalysis has mainly dealt with N4 ligands withpyrrole as subunits (porphyrin, phthalocyanine, etc.), while ligands constructedfrom pyridine subunits remain uncommon. The examples for comparing activeconfigurations are few and far between. Herein, the development of new N4cobalt complexes based on pyridine subunits is explored. After anchoring ontocarbon nanotubes, they can exhibit CO_2RR activity at a low overpotential of140 mV, and high activity from -0.30 to -0.60 V versus reference hydrogenelectrode with a selectivity of above 98. Excellent performance at large currentdensities can also be observed in a flow cell. In situ attenuated total reflectance-Fourier transform infrared spectroscopy proves that such electrocatalystsexhibit CO production at lower overpotential and moderate CO adsorptionability over a wide potential range. From density functional theory calculations,it is shown that a pyridine-based cobalt complex on a carbon substrate canreduce the Gibbs free energy for reactions further than its counterpart pyrrolebasedones. Further analysis proves that the semimetal behavior of optimizedd-orbitals may facilitate charge transfer and increase the activity. This providesa new insight for understanding catalytically active moieties in heterogeneousmolecular catalysts with ligands constructed from pyridine subunits.