Boosting CO2 Electrochemical Reduction with Atomically Precise Surface Modification on Gold Nanoclusters.

Thiolate-protected gold nanoclusters (NCs) are promising catalytic materials for the electrochemical CO2 reduction reaction (CO2 RR). In this work an atomic level modification of a Au23 NC is made by substituting two surface Au atoms with two Cd atoms, and it enhances the CO2 RR selectivity to 90-95 % at the applied potential between -0.5 to -0.9 V, which is doubled compared to that of the undoped Au23 . Additionally, the Cd-doped Au19 Cd2 exhibits the highest CO2 RR activity (2200 mA mg-1 at -1.0 V vs. RHE) among the reported NCs. This synergetic effect between Au and Cd is remarkable. Density-functional theory calculations reveal that the exposure of a sulfur active site upon partial ligand removal provides an energetically feasible CO2 RR pathway. The thermodynamic energy barrier for CO formation is 0.74 eV lower on Au19 Cd2 than on Au23 . These results reveal that Cd doping can boost the CO2 RR performance of Au NCs by modifying the surface geometry and electronic structure, which further changes the intermediate binding energy. This work offers insights into the surface doping mechanism of the CO2 RR and bimetallic synergism.