Electrochemical CO2 reduction catalyzed by atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 nanoclusters: probing the effect of multi-metal core on selectivity†
Doping metal nanoclusters (NCs) with another metal usually leads to superior catalytic performance toward CO2 reduction reaction (CO2RR), yet elucidating the metal core effect is still challenging. Herein, we report the systematic study of atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 NCs toward CO2RR. Au2Ag8Cu5 prepared by a site-specific metal exchange approach from Ag9Cu6 is the first case of trimetallic superatom with full-alkynyl protection. The three M15 clusters exhibited drastically different CO2RR performance. Specifically, Au7Ag8 demonstrated high selectivity for CO formation in a wide voltage range (98.1% faradaic efficiency, FE, at −0.49 V and 89.0% FE at −1.20 V vs. RHE), while formation of formate becomes significant for Ag9Cu6 and Au2Ag8Cu5 at more negative potentials. DFT calculations demonstrated that the exposed, undercoordinated metal atoms are the active sites and the hydride transfer as well as HCOO* stabilization on the Cu–Ag site plays a critical role in the formate formation. Our work shows that, tuning the metal centers of the ultrasmall metal NCs via metal exchange is very useful to probe the structure–selectivity relationships for CO2RR.