Monopalladium Substitution in Gold Nanoclusters Enhances CO₂ Electroreduction Activity and Selectivity

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.