Electrochemical CO 2 reduction catalyzed by atomically precise alkynyl-protected Au 7 Ag 8 , Ag 9 Cu 6 , and Au 2 Ag 8 Cu 5 nanoclusters: probing the effect of multi-metal core on selectivity.

Doping metal nanoclusters (NCs) with another metal usually leads to superior catalytic performance toward CO 2 reduction reaction (CO 2 RR), yet elucidating the metal core effect is still challenging. Herein, we report the systematic study of atomically precise alkynyl-protected Au 7 Ag 8 , Ag 9 Cu 6 , and Au 2 Ag 8 Cu 5 NCs toward CO 2 RR. Au 2 Ag 8 Cu 5 prepared by a site-specific metal exchange approach from Ag 9 Cu 6 is the first case of trimetallic superatom with full-alkynyl protection. The three M 15 clusters exhibited drastically different CO 2 RR performance. Specifically, Au 7 Ag 8 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 Ag 9 Cu 6 and Au 2 Ag 8 Cu 5 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 CO 2 RR.