It is challenging while critical to develop efficient catalysts that can achieve both high current density and high energy efficiency for electrocatalytic CO2 reduction (CO2R). Herein, we report a strategy of tailoring the surface electronic structure of an Ag catalyst via thiol ligand modification to improve its intrinsic activity, selectivity, and further energy efficiency toward CO2R. Specifically, interconnected Ag nanoparticles with residual thiol ligands on the surface were prepared through electrochemical activation of a thiol-ligand-based Ag complex. When it was used as a catalyst for CO2R, the thiol-ligand modified Ag exhibited high CO selectivity (>90%) throughout a wide electrode-potential range; furthermore, high cathodic energy efficiencies of >90% and >70% were obtained for CO formation at high current densities of 150 and 750 mA cm-2, respectively, outperforming the state-of-the-art Ag-based electrocatalysts for CO2 to CO conversion. The first-principle calculations on the reaction energetics suggest that the binding energies of the key intermediate -*COOH on Ag are optimized by the adsorbed thiol ligand, thus favoring CO formation while suppressing the competing H2 evolution. Our findings provide a rational design strategy for CO2 reduction electrocatalyst by electronic modulation through surface-adsorbed ligands.
Keywords: CO2 reduction; carbon monoxide; electrocatalysis; energy efficiency; silver; thiol ligand effect.