Electrodeposition of transition metals from highly concentrated solutions of ionic liquids

Five different ionic liquids (ILs), obtained by dissolving bistriflimide salts of Ag, Cu, Co, Ni and zinc in 1-butyl-3-methylimidazolium bistriflimide ([bmim][Tf2N]) were synthesized and electrochemically characterized by means of cyclic voltammetry and chronoamperometry. Silver-bearing IL represents the simplest electrochemical system since silver is present as uncoordinated or weakly coordinated Ag+ ions. Homogeneous and crack-free silver coatings were potentiostatically obtained from this ionic liquid and the nucleation and growth mechanism were determined. In contrast, copper-cobalt- and zinc-bearing systems were highly moisture sensitive. The presence of large amounts of water changes the nature of the coordination species present in the solution, facilitating the electroreduction of the metal complexes. However, in hydrated solutions we observe simultaneous hydrogen evolution, which impairs the electrochemical investigation of the metal nucleation and growth mechanism. Nevertheless, metallic deposits were obtained and their morphologies investigated as a function of the deposition potential and water content. Conversely, within the investigated electrochemical window, the Ni-bearing IL does not form electroactive species.