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.