Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO₂

Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic-level identification of active sites using atomically well-defined gold nanoclusters (Au NCs) Au₂₅, Au₃₈, and Au₁₄₄ as model catalysts in the electrochemical CO₂ reduction reaction (CO₂RR). The studied Au NCs exhibited remarkably high CO₂RR activity, which increased with increasing NC size. Electrochemical and X-ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO₂RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d-states for dethiolated Au sites. The structure–activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO₂RR activity was determined by the number of active sites on the cluster surface.