Single-Particle Spectroelectrochemistry: Plasmon-Mediated Catalytic Activity Enhancement by Electrochemical Surface Engineering in Individual Gold Nanorods

Understanding the enhancement of plasmon-mediated electrocatalytic activity in individual gold nanorods (AuNRs) remains limited. Herein, we report a single-particle spectroelectrochemical study on the electrochemical growth and catalytic role of Cu and CuxS layers on AuNRs, formed via controlled deposition potentials. Underpotential deposition (UPD) of Cu on AuNRs induces a blueshift and intensity enhancement in the localized surface plasmon resonance (LSPR) spectrum, attributed to increased electron density from Cu. At more cathodic potentials, bulk Cu─primarily as lumpy CuxO─is deposited, introducing a new Cu-related LSPR peak. In situ LSPR tracking reveals insights into the electrochemical kinetics of Cu2+ species and its effect on AuNR optoelectronic properties. Subsequent sulfur deposition forms a rough CuxS semiconductor layer, causing LSPR damping, which is reversible upon sulfur removal. The intrinsic plasmonic activity of AuNRs is enhanced by Cu deposition through elevated electron density, while the CuxS layer further boosts catalytic performance via interfacial charge separation. Therefore, our single-particle spectroelectrochemical study provides new insights into the mechanisms of plasmon-mediated catalysis and catalytic enhancement enabled by electrochemically formed metallic layers on individual AuNRs for the detection of nitroaromatics in chemical industries. This study also presents a strategy for tuning the optoelectronic and catalytic properties of individual AuNRs through electrochemical surface engineering.