Transition-metal-mediated electrocatalytic CO2 reduction: from nanoparticles to single-atom catalysts

With the rapid development of the global economy, energy crisis and environment issues have become increasingly prominent. Carbon dioxide (CO2) is a primary greenhouse gas (CHG), while it could also be a valuable carbon source. In recent years, electrochemical CO2 reduction reaction (ECR) has received considerable attention among various CO2 conversion technologies. Nevertheless, physicochemical properties of the CO2 molecule make electrochemical conversion of CO2 challenging. Despite that great progress has been made to exploit electrocatalysts for ECR, the process is still impeded by the sluggish kinetics, poor product selectivity, catalyst deactivation, and high overpotential. Therefore, it is highly desirable to develop electrocatalysts with high activity and selectivity for ECR. Loading metal nanoparticles (NPs) on two-dimensional (2D) materials as electrocatalysts for ECR has been reported extensively in literature. Herein, we studied silver loaded boron-doped g-C3N4 nanocomposite (Ag-B-g-C3N4) for efficient ECR to CO by combined experimental work and first-principles study. Theoretical simulation demonstrated that introduction of Ag NPs and the B atom could greatly decrease the adsorption free energy for the *COOH intermediate generation. B-g-C3N4 could not exhibit the obvious enhancement of ECR performance, while the Ag-B-g-C3N4 catalyst exhibited a total current density of 2.08 mA cm–2 and a CO Faradaic efficiency of 93.2% under the potential of −0.8 V vs the reversible hydrogen electrode (RHE). It has been well established that the catalytic activity can be further improved by reducing the size of catalysts. Specifically, single atoms catalysts (SACs) with single atom as active center have aroused huge interest due to maximum atom utilization and excellent performance in various catalytic reactions. Therefore, we investigated the single transition metal atoms (V, Cr, Mn, Fe, Co, Ni) embedded O group terminated Nb2N monolayer (Nb2NO2) as ECR catalysts by first-principles calculation. It is found that ...