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 Cu _<i>x</i> S layers on AuNRs, formed <i>via</i> 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 Cu _<i>x</i> Ois deposited, introducing a new Cu-related LSPR peak. <i>In situ</i> LSPR tracking reveals insights into the electrochemical kinetics of Cu²⁺ species and its effect on AuNR optoelectronic properties. Subsequent sulfur deposition forms a rough Cu _<i>x</i> S 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 Cu _<i>x</i> S layer further boosts catalytic performance <i>via</i> 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.