Deciphering Electrocatalytic Activity in Cu Nanoclusters: Interplay between Structural Confinement and Ligands Environment

Ligand-protected copper nanoclusters (Cu NCs) with atomic precision have emerged rapidly due to their fascinating structural architectures and versatile catalytic properties, making them ideal for investigating structure–activity relationships. Despite their potential, challenges such as stability issues and limited structural diversity have restricted deeper exploration. In this study, three distinct Cu NCs were synthesized using a one-pot reduction strategy by carefully modifying reaction conditions. Intriguingly, the same p-toluenethiol ligand produced two different geometries, while varying ligand with m-aminobenzethiol—yielded clusters with similar geometric architectures. These NCs were evaluated for electrocatalytic CO2 reduction, uncovering diverse catalytic activities and product selectivity. Experimental and theoretical analyses revealed that the interplay between the core structure confinement and surface ligand environment governs their catalytic behavior. Specifically, the Cu11 NC with p-toluenethiol ligand exhibited selectivity toward HCOOH production (FEHCOOH~45% at -1.2 V vs. RHE), whereas substituting p-toluenethiol with m-aminobenzethiol shifted the selectivity to the competitive side reaction (FEH2~82% at -1.2 V vs. RHE). Conversely, altering the geometry of Cu18 NC while retaining the p-toluenethiol ligand decreased such selectivity (FEHCOOH~35% at -1.2 V vs. RHE). These findings highlight the tunability of Cu NCs for tailored catalytic applications through precise control of their structure and surface chemistry.