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 are synthesized using a one-pot reduction strategy by carefully modifying reaction conditions. Intriguingly, the same p-toluenethiol ligand produces two different geometries, while varying ligands with m-aminobenzethiol-yielded clusters with similar geometric architectures. These NCs are evaluated for electrocatalytic CO₂ reduction, uncovering diverse catalytic activities and product selectivity. Experimental and theoretical analyses reveal that the interplay between the core structure confinement and surface ligand environment governs their catalytic behavior. Specifically, the Cu₁₁ NC with p-toluenethiol ligand exhibits selectivity toward HCOOH production (FE_HCOOH∼45% at -1.2 V vs RHE), whereas substituting p-toluenethiol with m-aminobenzethiol shifted the selectivity to the competitive side reaction (FE_H2∼82% at -1.2 V vs RHE). Conversely, altering the geometry of Cu₁₈ NC while retaining the p-toluenethiol ligand decreases such selectivity (FE_HCOOH∼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.