Step‐Edge Functionalization by N‐Heterocyclic Carbenes Enhances Catalytic Activity in Electrochemical CO ₂ Reduction

Atomic step‐edges on metallic surfaces are highly active catalytic sites due to their reduced coordination and modified electronic structure. Yet, approaches to organic ligand functionalization on the single‐molecule level have largely targeted flat terrace geometries, whereas site‐specific step‐edge functionalization remains unaddressed. This study shows that decorating the atomically defined step‐edges of Au(788) with N‐heterocyclic carbenes (NHCs) enhances their catalytic activity toward reduction compared to undecorated metallic step‐edges. Using high‐resolution scanning probe microscopy, an upright‐tilted adsorption geometry and a unified binding mode of three different NHCs at step‐edges are revealed. The exceptional stability of these well‐defined nanostructures allows the use of the single‐crystalline samples as working electrodes in electrochemical experiments. Photoelectron spectroscopy and theoretical simulations correlate charge transfer and conformational details with their catalytic performance. By combining macroscopic electrochemical experiments with single‐molecule microscopy, this study highlights NHC step‐edge functionalization as an effective approach to design highly selective and efficient catalysts.