Underpotential Deposition of Silver on Gold for Surface Catalysis of Plasmon-Enhanced Reduction of 4-Nitrothiophenol

Underpotential deposition (UPD) in electrochemistry can be used to form heterometal deposits on substrates at a monolayer level, altering the surface characteristics. In this work, we demonstrated the application of UPD metals in catalyzing photoreactions of adsorbed molecules under the excitation of surface plasmons. For a monolayer of 4-nitrothiophenol (4-NTP) on a roughened Au substrate, the reduction and dimerization to 4,4'-dimercaptoazobenzene (DMAB) were monitored under conditions of Ag UPD using electrochemical surface-enhanced Raman spectroscopy (EC-SERS). Formation of DMAB was enhanced on the Ag surface deposited via UPD between the Au substrate and the 4-NTP layer. The structures of the 4-NTP layer and the plasmonic surface remained intact during Ag UPD. Therefore, we suggest that the surface of UPD Ag played a catalytic role in reduction of the nitro group. Overall, surface modification via UPD offers a potential strategy for controllably tuning the surface and interface chemistry.