Alkynyl-protected Cu₆₇ nanocluster superatom: Structure anatomy and electrochemical CO₂ 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; Ph and OAc refer to phenyl group and acetate, respectively) superatomic nanocluster, which possesses a hierarchical metal core structure of Cu₅@Cu₂₆@Cu₃₆. Cu₆₇ was synthesized by a one-pot reduction strategy in which phenylacetylene drives 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), deeply 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. reversible hydrogen electrode (RHE), among which the FE of ethylene ( ${\text{FE}}_{{\mathrm{C}}_2{\mathrm{H}}_4}$) is 39.01%. The excellent catalytic performance from Cu₆₇ is superior to 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 members of alkynyl-protected high-nuclearity superatomic Cu nanoclusters, but also provides atom-level mechanistic insights on employing Cu nanoclusters for eCO₂RR to produce highly valuable products.