Investigation of Enhanced Water Oxidation under Plasmon–Nanocavity Strong Coupling Using In Situ Electrochemical Surface-Enhanced Raman Spectroscopy

Strong coupling between a localized surface plasmon resonance (LSPR) at the surface of metal nanoparticles (NPs) and a Fabry–Pérot (FP) nanocavity can facilitate photochemical reactions. It is very interesting and critical to study the enhancement mechanism of plasmon-induced chemical reactions under plasmon–nanocavity strong coupling to further improve the photochemical reaction efficiency. In this study, we fabricated a LSPR–FP nanocavity strong coupling photoelectrode composed of Au–Ag alloy NPs, titanium dioxide (TiO2), and a Au film as a working electrode to investigate the mechanism of water oxidation enhancement under plasmon–nanocavity strong coupling conditions. In situ electrochemical surface-enhanced Raman spectroscopy measurements were performed to detect the intermediate species of water oxidation under a series of electrochemical potentials. The Au–O and Au–OH stretching vibrations related to the intermediates of water oxidation were investigated. Compared with the Au–Ag alloy NPs/TiO2 structure without strong coupling, the surface-enhanced Raman spectroscopy signal of the Au–O stretching vibration on the strong coupling electrode exhibited a more negative onset potential, indicating that more efficient water oxidation occurred on it. This efficient water oxidation in the strong coupling photoelectrode was considered a result of the quantum coherence between the Au–Ag alloy NPs through the nanocavity.