Electrochemical CO₂ reduction catalyzed by atomically precise alkynyl-protected Au₇Ag₈, Ag₉Cu₆, and Au₂Ag₈Cu₅ nanoclusters: probing the effect of multi-metal core on selectivity

Abstract

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 <i>vs.</i> 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 <i>via</i> metal exchange is very useful to probe the structure-selectivity relationships for CO₂RR.