Ligand exchange-based synthesis of azide-functionalized Cu nanospheres as a platform for Mn complex immobilization and electrochemical CO2 reduction

Abstract

Cu nanoparticles (NPs) are applied widely as catalysts in different processes, owing to their interesting redox capabilities, relatively high abundance, and low cost. The introduction of stabilizing organic ligands on the surface of NPs allows for the creation of tailored molecule-metal interfaces with unique properties. Furthermore, by decorating the ligand sphere with chemical handles that enable versatile post-synthesis modifications, the reactivity of Cu NPs may be tuned to fit a desired application. An important application of Cu NPs is as a hydrocarbon-generating catalyst in the electrochemical CO₂ reduction reaction, which represents a promising approach for seasonal storage of electrical energy by converting CO₂ into value-added small molecules. The ability of Cu to produce hydrocarbons has been directly linked to a high local concentration of surface-adsorbed CO on Cu, which can be achieved with so-called tandem catalytic systems. In this study, we demonstrate the functionalization of colloidal Cu nanospheres with azide-decorated aliphatic ligands by affinity-driven partial ligand exchange reactions, relying on the strong binding of thiols to the Cu surface. We identify correlations between the extent of modification and dispersion stability and validate the successful ligand exchange through a combination of spectroscopic techniques. Representing a versatile platform for further functionalization, the azide handle is utilized for the immobilization of an organometallic Mn complex, which is shown to produce CO and formate in the CO₂RR. Exploring this assembly as a tandem catalyst in the CO₂RR highlights the importance of potential alignment between the catalytic components in these systems, as the results indicate an insufficient CO production by the Mn complex at potentials where the Cu NPs facilitate the further reduction of this intermediate.