DFT Study on the Electrocatalytic Reduction of CO2 to CO by a Molecular Chromium Complex

A variety of molecular transition metal-based electrocatalysts for the reduction of carbon dioxide (CO2) have been developed to explore the viability of utilization strategies for addressing its rising atmospheric concentrations and the corresponding effects of global warming. Concomitantly, this approach could also meet steadily increasing global energy demands for value-added carbon-based chemical feedstocks as nonrenewable petrochemical resources are consumed. Reports on the molecular electrocatalytic reduction of CO2 mediated by chromium (Cr) complexes are scarce relative to other earth-abundant transition metals. Recently, our group reported a Cr complex that can efficiently catalyze the reduction of CO2 to carbon monoxide (CO) at low overpotentials. Here, we present new mechanistic insight through a computational (density functional theory) study, exploring the origin of kinetic selectivity, relative energetic positioning of the intermediates, speciation with respect to solvent coordination and spin state, as well as the role of the redox-active bipyridine moiety. Importantly, these studies suggest that under certain reducing conditions, the formation of bicarbonate could become a competitive reaction pathway, informing new areas of interest for future experimental studies.