How Carbene Ligands Transform AuAg Alloy Nanoclusters for Electrocatalytic Urea Synthesis

Abstract

Metal nanoclusters stabilized by N-heterocyclic carbene (NHC) ligands have attracted increasing interest for their special structures and diverse applications. However, developing synthetic strategies and extending the database of NHC-protected nanoclusters are still challenging tasks. In this work, a novel and rapid synthetic method is developed to prepare AuAg alloy nanocluster ligated by carbene based on the reactivity of nanoclusters. The rod-like carbene-capped bimetal nanocluster, [Au₁₃Ag₁₂(PPh₃)₈(BMIm)₂I₈]SbF₆ (Au₁₃Ag₁₂ : BMIm), was achieved and characterized by a series of techniques. The alloy nanocluster consists of two vertex-sharing icosahedrons and carbene ligands, phosphine ligands, and I atoms. Interestingly, the introduced carbene ligands show strong coordination capabilities with Au, enhancing the interaction between metal core and ligands. To the best of our knowledge, the carbene-capped Au₁₃Ag₁₂ : BMIm nanocluster is the first of its kind to show higher thermostability and higher sensitivity to light compared with the homogeneously capped analogue nanocluster ([Au₁₃Ag₁₂(PPh₃)₁₀I₈]SbF₆). Density functional theory calculations attribute these properties to a unique delocalization of electrons within the frontier orbitals. Finally, the Au₁₃Ag₁₂ : BMIm anchored on NiFe-LDH exhibits remarkable electrocatalytic activity in the electrosynthesis of urea from NO₃⁻ and CO₂, achieving a urea production rate of 29.5 mmol g_cat⁻¹ h⁻¹ with a Faradaic efficiency of 34 % at −0.5 V (vs. RHE).