Nanolaminate Nano-Optoelectrodes Enable Dual-Channel Plasmon-Enhanced Raman Spectroscopy for Electrochemistry

Abstract

In situ monitoring of short-lived transition states (TSs) is crucial for understanding electrochemical reaction mechanisms but remains challenging. Conventional electrochemical surface-enhanced Raman spectroscopy (EC-SERS) primarily provides vibrational information, with limitations in hotspot reproducibility and often overlooking electronic information associated with TSs. This study introduces a dual-channel EC-SERS strategy using nanolaminate nano-optoelectrode (NLNOE) devices, integrating plasmon-enhanced vibrational Raman scattering (PE-VRS) and plasmon-enhanced electronic Raman scattering (PE-ERS) to concurrently probe TS dynamics within electrically connected plasmonic nanocavities. Using the AgCl(s) + e⁻⇌Ag(s) + Cl⁻(aq) redox system, this approach distinct PE-VRS and PE-ERS signatures of the (AgCl)^* TS. Notably, a significant increase in PE-ERS signals concurrent with (AgCl)^* TS emergence, characterized by filled bonding and unoccupied antibonding orbitals with negligible energy gaps. This enhanced PE-ERS signal correlates with increased (AgCl)^* TS polarizability, leading to amplified PE-VRS signals due to enhanced electron cloud distortion. By modulating Cl⁻ ion concentrations via electrolyte composition (1× PBS and 1× PBS-equivalent KH₂PO₄) while maintaining constant total ion concentration, the competition between Ag/AgCl and Ag/AgH₂PO₄ redox reactions within Ag nanolayers is influenced. These results demonstrate the capability of dual-channel EC-SERS to distinguish interfacial redox reactions based on distinct electronic and vibrational signatures associated with covalent and ionic bond characteristics.