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 (FE_C2H4) 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.