Atomically precise gold nanoclusters provide opportunities for correlating the structure and electrocatalytic properties at the atomic level. Here, we report the single-atom doping effect on CO2 reduction by comparing monopalladium-doped Pd1Au24 and homogold Au25 nanoclusters (both protected by thiolates) that share an identical core structure. Experimental results show that single Pd-substitution drastically inhibits H2 evolution at large currents; thus, Pd1Au24 can convert CO2 to CO with ∼100% faradaic efficiency ranging from −0.6 (onset) to −1.2 V (vs RHE), while Au25 starts to decline at −0.9 V. Theoretical simulations reveal that the Pd dopant influences the Au nanocluster properties through a unique mechanism different from that in conventional alloy nanoparticles. The surface S atoms of the thiolate ligand are identified as the active sites (with the Au13 core as the electron reservoir) for selective CO2 reduction, whereas undercoordinated Au atom active sites are predicted to favor H2 evolution. Thermodynamic analysis of the ligand removal process predicts that Pd1Au24 should retain a larger population of S atom active sites under cathodic potentials compared with Au25, which extends the potential range for selective CO2 reduction. Our results demonstrate that single-atom substitution can substantially improve the CO2 reduction selectivity of gold nanoclusters at large potentials. The dopant-induced ligand stability may serve as a design strategy to modify the stability of catalytic active sites under harsh conditions.

Thiolate‐protected gold nanoclusters (NCs) are promising catalytic materials for the electrochemical CO2 reduction reaction (CO2RR). 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 CO2RR 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 Au19Cd2 exhibits the highest CO2RR 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 CO2RR pathway. The thermodynamic energy barrier for CO formation is 0.74 eV lower on Au19Cd2 than on Au23. These results reveal that Cd doping can boost the CO2RR 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 CO2RR and bimetallic synergism.

Electrocatalytic hydrogen evolution reaction (HER) holds promise in the renewable clean energy scheme. Crystalline Au and Ag are, however, poor in catalyzing HER, and the ligands on colloidal nanoparticles are generally another disadvantage. Herein, we report a thiolate (SR)-protected Au 36 Ag 2 (SR) 18 nanocluster with low coverage of ligands and a core composed of three icosahedral (I h ) units for catalyzing HER efficiently. This trimeric structure, together with the monomeric I h Au 25 (SR) 18− and dimeric I h Au 38 (SR) 24 , constitutes a unique series, providing an opportunity for revealing the correlation between the catalytic properties and the catalyst's structure. The Au 36 Ag 2 (SR) 18 surprisingly exhibits high catalytic activity at lower overpotentials for HER due to its low ligand-to-metal ratio, low-coordinated Au atoms and unfilled superatomic orbitals. The current density of Au 36 Ag 2 (SR) 18 at −0.3 V vs RHE is 3.8 and 5.1 times that of Au 25 (SR) 18 − and Au 38 (SR) 24 , respectively. Density functional theory (DFT) calculations reveal lower hydrogen binding energy and higher electron affinity of Au 36 Ag 2 (SR) 18 for an energetically feasible HER pathway. Our findings provide a new strategy for constructing highly active catalysts from inert metals by pursuing atomically precise nanoclusters and controlling their geometrical and electronic structures.

S/Se atoms at the metal–ligand interface can play an important role in determining the overall electrocatalytic performance of Au nanoclusters.