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.