Seed-mediated synthesis of NHC-stabilised Cu@Au core–shell nanoparticles from an NHC-Au(i) complex

N-heterocyclic carbenes (NHCs) provide a robust platform for the stabilisation and functionalisation of metal nanoparticles. Extending this ligand class to air-sensitive copper-based nanomaterials is particularly attractive, but remains challenging because copper nanoparticles readily oxidise under ambient conditions. Here, we report the seed-mediated synthesis of 9 nm copper–gold core–shell nanoparticles (CSNPs) with a ∼2 nm gold shell, prepared by reducing a NHC-Au(i) complex on pre-formed copper nanoparticle seeds. The resulting samples, denoted as IC12@CSNP and IC12@CSNPNHC, were characterised by X-ray Photoelectron Spectroscopy (XPS) and Surface-Enhanced Raman Spectroscopy (SERS), confirming surface binding of IC12 ligands. Scanning Transmission Electron Microscopy (STEM) and High-Resolution Transmission Electron Microscopy (HRTEM) verified the distinct gold shell and copper core. The gold shell helps preserve the metallic character of the copper core upon exposure to air. Both IC12@CSNP and IC12@CSNPNHC exhibit electrocatalytic activity for syngas production under CO₂ reduction conditions, with the H₂ : CO ratio tunable from 0.9 : 1 to 2.7 : 1 by varying the applied potential. This work establishes a straightforward synthetic route to air-stable, NHC-functionalised copper–gold core–shell nanoparticles with well-defined structure and tunable catalytic behaviour.