Single‐particle spectroelectrochemistry: Electrochemically engineered Cu adlayers boost plasmon‐driven electrocatalysis in gold nanorods

Understanding plasmon‐mediated electrocatalytic activity enhancement in single gold nanorods (AuNRs) is still limited. Herein, we present the formation of copper (Cu) layers on individual AuNRs immobilized on an ITO substrate as a function of potential and their effect on the localized surface plasmon resonance (LSPR) property of individual AuNRs by in situ monitoring of LSPR spectral changes in AuNRs via dark‐field scattering microscopy and spectroscopy. The Cu adlayer formation on AuNR within the under potential deposition range increases the free electron density of Cu@AuNR, which affects the LSPR spectrum, leading to increased peak intensity and a blueshift. The overpotential deposition resulted in the formation of bulky Cu deposits and an increase in the size of individual AuNRs, leading to an additional Cu LSPR peak at higher energy levels, in addition to the peak for Au. The high electron density donated by Cu to Au facilitated the generation of energetic hot electrons at the tip of Cu@AuNR particles, thereby enhancing electrocatalytic activity, as confirmed through the electrocatalytic reduction of 4‐nitrophenol to 4‐aminophenol in the single‐particle system.