Atomically precise alkynyl-protected Ag₂₀Cu₁₂ nanocluster: Structure analysis and electrocatalytic performance toward nitrate reduction for NH₃ synthesis

Electrochemical nitrate reduction reaction (NtrRR) has been emerging as an appealing route for both water treatment and NH₃ synthesis. Herein, we report the structure analysis and electrocatalytic performance of a novel homoleptic alkynyl-protected Ag₂₀Cu₁₂ nanocluster (Ag₂₀Cu₁₂ in short) with atomic precision, which has eight free electrons and displays characteristic absorbance feature. Single crystal X-ray diffraction (SC-XRD) discloses that, it adopts a Ag₁₄ kernel capped by three Ag₂Cu₄(C≡CAr^F)₈ metal–ligand binding motifs in the outer shell. Ag₂₀Cu₁₂ exhibited excellent catalytic performance toward NtrRR, as manifested by the superior NH₃ Faradaic efficiency (FE, 84.6%) and yield rate (0.138 mmol·h⁻¹·mg⁻¹) than the homoleptic alkynyl-protected Ag₃₂ nanoclusters. Additionally, it demonstrates good catalytic recycling capability. Density functional theory (DFT) calculations revealed that, the de-ligated Ag₂₀Cu₁₂ cluster can expose the available AgCu bimetallic sites as the efficient active sites for NH₃ formation. In particular, the participation of Cu sites greatly facilitates the initial capture of NO₃⁻ and simultaneously promotes the selectivity of the final product. This study discovers a novel homoleptic alkynyl-protected AgCu superatom, and offers a great example to elucidate the structure–performance relationship of bimetallic catalyst for NtrRR and other multiple protons/electrons coupled electrocatalytic reactions.