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 Au-25 nanoclusters (both protected by thiolates) that share an identical core structure. Experimental results show that single Pd-substitution drastically inhibits H-2 evolution at large currents; thus, Pd1Au24 can convert CO2 to CO with similar to 100% faradaic efficiency ranging from -0.6 (onset) to -1.2 V (vs RHE), while Au-25 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 Au-13 core as the electron reservoir) for selective CO2 reduction, whereas undercoordinated Au atom active sites are predicted to favor H-2 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 Au-25, 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.