ИСТИНА

Owing to their unique properties, air- and water-stable room-temperature ionic liquids (ILs) are an excellent alternative medium for electrodeposition of metals, alloys, and semiconductor materials [1]. Most ILs are characterized by good intrinsic ionic conductivity, nonvolatility, high thermal stability, and wide electrochemical window. They afford ample opportunities for elaboration of electrodeposition processes that are inefficient or difficult to realize in aqueous solutions or solutions based on organic solvents. Furthermore, physico-chemical properties of ILs can be tuned by combining various cations and anions. This led to intensive studies of electrodeposition in ILs [2]. However, the fundamental understanding of electrodeposition processes in ILs is still to be developed [3]. Here, we focus on the study of initial stages of metallic silver electrodeposition on Pt and Au single crystal surfaces in ILs with dicyanamide anion. These ILs manifest rather low viscosity and provide good solubility of Ag salts. In this study, we employed conventional electrochemical techniques in combination with in situ and ex situ scanning probe microscopy (in situ STM and ex situ AFM). The possibility of epitaxial and 2D deposition of silver onto single crystal surfaces from ILs is investigated by in situ STM. Furthermore, we also examine stability of gold and platinum single crystal surfaces in chosen dicyanamide–containing ILs in the absence of a silver salt. It is shown that there is a fundamental difference in the behavior of Pt and Au electrodes. The voltammogram (CV) of Ag deposition manifests a nucleation loop in case of Pt(111) and no such loop and indeed no intersection of the anodic and cathodic CV scans in the case of Au(111) and Au(100), both in 1-butyl-3-methylimidazolium dicyanamide ([BMIm][DCA]) and in 1-butyl-3-methylpyrrolidinium dicyanamide ([BMPy][DCA]). Ex situ AFM and in situ STM data show that the deposit on Pt(111) consists of separate crystallites, while on Au(111) and Au(100) the deposit represents 2D Ag islands and then quasi-2D structure of 10–20 nm nanoparticles and the further increase in overpotential results in appearance of 3D Ag crystallites on the 2D layer surface. Another interesting phenomenon observed in these systems is Ag UPD. Almost no Ag UPD is observed on Pt(111) (only 0.06 ML in [BMIm][DCA]), while the UPD coverage on gold single crystals is significant and reaches at least 1/2 ML on Au(100) in [BMIm][DCA]. One can assume that the presence of a sufficiently large amount of Agad adatoms on the Au surface can result in activation of Ag phase deposition. In case of Pt(111), Ag adatoms are absent or their amount is negligible, so formation of the Ag phase deposit requires higher overpotentials.