Theory-Guided Modulation of Optimal Silver Nanoclusters toward Efficient CO₂ Electroreduction

Electrochemical CO2 reduction reaction (CO2RR), when powered with intermittent but renewable energies, holds an attractive potential to close the anthropogenic carbon cycle through efficiently converting the exorbitantly discharged CO2 to value-added fuels and/or chemicals and consequently reduce the greenhouse gas emission. Through systematically integrating the density functional theory calculations, the modeling statistics of various proportions of CO2RR-preferred electroactive sites, and the theoretical work function results, it is found that the crystallographically unambiguous Ag nanoclusters (NCs) hold a high possibility to enable an outstanding CO2RR performance, particularly at an optimal size of around 2 nm. Motivated by this, homogeneously well-distributed ultrasmall Ag NCs with an average size of ∼2 nm (2 nm Ag NCs) were thus synthesized to electrochemically promote CO2RR, and the results demonstrate that the 2 nm Ag NCs are able to achieve a significantly larger CO partial current density [j(CO)], an impressively higher CO Faraday efficiency of over 93.8%, and a lower onset overpotential (η) of 146 mV as well as a remarkably higher energy efficiency of 62.8% and a superior stability of 45 h as compared to Ag nanoparticles (Ag NPs) and bulk Ag. Both theoretical computations and experimental results clearly and persuasively demonstrate an impressive promotion effect of the crystallographically explicit atomic structure for electrochemically reducing CO2 to CO, which exemplifies a novel design approach to more benchmark metal-based platforms for advancing the practically large-scale CO2RR application.