Body-Centered-Cubic-Kernelled Ag 15 Cu 6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO 2 Electroreduction.

While atomically monodisperse nanostructured materials are highly desirable to unravel the size- and structure-catalysis relationships, their controlled synthesis and the atomic-level structure determination pose challenges. Particularly, copper-containing atomically precise alloy nanoclusters are potential catalyst candidates for the electrochemical CO 2 reduction reaction (eCO 2 RR) due to high abundance and tunable catalytic activity of copper. Herein, we report the synthesis and total structure of an alkynyl-protected 21-atom AgCu alloy nanocluster [Ag 15 Cu 6 (C≡CR) 18 (DPPE) 2 ] - , denoted as Ag 15 Cu 6 (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene; DPPE: 1,2-bis(diphenylphosphino)ethane). The single-crystal X-ray diffraction reveals that Ag 15 Cu 6 consists of an Ag 11 Cu 4 metal core exhibiting a body-centered cubic (bcc) structure, which is capped by 2 Cu atoms, 2 Ag 2 DPPE motifs, and 18 alkynyl ligands. Interestingly, the Ag 15 Cu 6 cluster exhibits excellent catalytic activity for eCO 2 RR with a CO faradaic efficiency (FE CO ) of 91.3% at -0.81 V (vs the reversible hydrogen electrode, RHE), which is much higher than that (FE CO : 48.5% at -0.89 V vs RHE) of Ag 9 Cu 6 with bcc structure. Furthermore, Ag 15 Cu 6 shows superior stability with no significant decay in the current density and FE CO during a long-term operation of 145 h. Density functional theory calculations reveal that the de-ligated Ag 15 Cu 6 cluster can expose more space at the pair of AgCu dual metals as the efficient active sites for CO formation.