Probing Hot-Carrier and Thermal Contributions to Plasmon-Assisted Electrochemistry at Gold Nanorods

Plasmon-assisted electrochemistry has emerged as a powerful strategy to enhance interfacial charge transfer by exploiting localized surface plasmon resonance (LSPR) in metallic nanostructures. Under resonant illumination, gold nanorods (AuNRs) generate energetic hot electron–hole pair and localized heating, both of which may influence electron transfer kinetics. However, decoupling both contributions remains challenging. Here, we present a plasmonic transducer system based on AuNRs anchored to mercaptopropyl triethoxysilane-modified indium tin oxide electrodes (AuNRs/MPTES-ITO) and investigate the photoelectrochemical behavior under low-intensity near-infrared (780 nm) LED illumination. Using chronoamperometry, in situ fiber-optic thermometry to measure the electrode-bulk surrounding temperature, and COMSOL simulations, we show that faradaic current enhancement does not follow the gradual temperature increase but instead reaches a rapid steady state, indicating hot-electron-driven effects. The heterogeneous electron-transfer rate constant determined via scanning electrochemical microscopy (SECM) approach curves reveals a 45 ± 4% (n = 9) increase under illumination for non-capped-AuNRs/MPTES-ITO, while MPTES-ITO shows only a 15 ± 2% (n = 9) enhancement. SECM mapping further visualizes localized faradaic current amplification on AuNR-rich regions. Together, these results suggest that even at low power densities (307.7 mW·cm–2), longitudinal LSPR excitation in AuNRs efficiently generates hot carriers capable of enhancing electrochemical reactions with a nondominant thermal contribution. This study provides a spatially resolved approach to investigate hot-carrier and photothermal pathways in plasmon-assisted electrochemistry.