Alkynyl-protected Cu ₆₇ nanocluster superatom: Structure anatomy and electrochemical CO ₂ reduction study

Atomically precise high-nuclearity Cu nanoclusters (Cu atom number > 50) with both Cu(I) and Cu(0) species have been rarely reported due to the inherent instability of Cu(0) species. Herein, we report a C3 symmetric alkynyl-protected [Cu67(C≡CPh)24(OAc)18]- (Cu67) superatomic nanocluster, which possesses a hierarchical metal core structure of Cu5@Cu26@Cu36. Cu67 is synthesized by a one-pot reduction strategy in which phenylacetylene drive the assembly of a nested architecture stabilized by synergistic μ-coordinated alkynyl ligands (μ4/μ5 modes) and κ2-bridged acetates. Remarkably, when Cu67 is used for electrochemical CO2 reduction reaction (eCO2RR), deep reduced hydrocarbon chemicals especially the C2+ products with high selectivity are acquired. Specifically, Cu67 achieves a Faradaic efficiency (FE) of 56.32% for the total C2+ products at -0.9 V vs. RHE, among which the FE of ethylene (FEC2H4) is 39.01%. The excellent catalytic performance from Cu67 is superior than most of the recently reported Cu-nanocluster-based catalysts. In-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) study reveals the reaction pathway and identifies the key intermediate *COCHO for yielding C2+ products. Density functional theory (DFT) calculations systematically elucidate the reaction mechanism of eCO2RR on Cu67 to generate CO and C2H4, where the transformation from *CO to *CHO is the rate-determining step for generating the C2+ products. This work not only enriches the family member of alkynyl-protected high-nuclearity superatomic Cu nanoclusters, but also provides atomical-level mechanistic insights on employing Cu nanoclusters for eCO2RR to produce highly valuable products.