Underpotential Deposition of Silver on Au(111) from an Air- and Water-Stable Ionic Liquid Visualized by In-Situ STM

There is a steadily increasing interest in room-temperature ionic liquids (ILs) as media for metal electrodeposition. However, the fundamental understanding of the underlying surface processes at the electrode/IL interface and of the initial stages of electrodeposition is still at a very preliminary stage. In this article, we investigate the underpotential deposition (upd) of Ag on a well-defined Au(111) single crystal surface from an air- and water-stable IL, 1-butyl-1-methylpyrrolidinium dicyanamide [BMP] [DCA]. By employing in-situ scanning tunneling microscopy (STM), we could visualize individual stages of the Ag upd process as a function of the applied electrode potential and correlate voltammetric responses to the obtained STM data. The initial Ag upd process results in the formation of an Ag-(4 x 4) lattice, which is further transformed into a pseudomorphic Ag-(1 x 1) monolayer at the underpotential of similar to 40 mV. The structural stability of the Au(111) surface in [BMP][DCA] is also examined in the absence of Ag+ ions in both the negative and positive potential regions.