Electrodeposition Of Copper In Cu(BF₄)₂-[bmim]BF₄ And CuSO₄-H₂O-[bmim]BF₄ Systems

In this paper, the 1-butyl-3-methylimidazolium chloride (BMIC) intermediate and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF₄) ionic liquid were prepared. The electrodeposition of copper on different substrates were studied in Cu(BF₄)₂-[bmim]BF₄ system at 100℃and in CuSO₄-H₂O-[bmim]BF₄ system at 60℃, respectively.The determined electrochemical window of [bmim]BF₄ is 2.9V, the anodic limit potential is +1.7V and the cathodic one is -1.2V.Electrical conductivities of [bmim]BF₄ and CuSO₄-H₂O-[bmim]BF₄ systems were measured. The relations of electrical conductivity with solution composition and temperature were obtained. In CuSO₄-H₂O-[bmim]BF₄ system, the electrical conductivity decreased with increasing the content of [bmim]BF₄ in the range of 0～5%(v/v). It was found that the electrical conductivities of [bmim]BF₄ and CuSO₄-H₂O-[bmim]BF₄ systems were increased with increasing temperature, which can be described by Kohlraush empirical formula, whereκis electrical conductivity in S·m^-1,κ₀ refers to electrical conductivity at room temperature in S·m^-1, t is temperature in℃, a andβare temperature coefficients, t₀ is room temperature (25℃).The electrode process of CuSO₄-H₂O-[bmim]BF₄ system was studied by chronopotentiometry, cyclic voltammetry and linear scanning voltammetry. It was shown that the cathode potentials become more and more negative with the increasing of [bmim]BF₄ content. The more negative the cathode potential is, the lager the current density. It was found that the cathodic process of CuSO₄-H₂O-[bmim]BF₄ system was a quasi-reversible process. The cathode reaction was found to be simultaneously controlled by diffusion and electrochemical reaction from the cathodic polarization overpotential and cathodic polarization curves.It is demonstrated that copper can dissolve in [bmim]BF₄ ionic liquid at room temperature and the dissolution rate is enhanced with increasing temperature. The copper dissolved in the [bmim]BF₄ ionic liquid is found to exist in the form of Cu²⁺ since the light blue and brightly needle Cu(BF₄)₂ crystals was obtained, implying that [bmim]BF₄ ionic liquid has oxidation ability. The dissolution of copper in the [bmim]BF₄ ionic liquid offers a new method to provide the target metal ions for electrodeposition in ionic liquids.The morphologies of copper deposits were analyzed by scanning electron microscopy. The typical sheet layer of the surface of cathode copper deposits and the tree crystal on the edge of cathode were observed. It was shown that the copper deposits on the edge of cathode are thicker than those in the interior region and the tree crystal phenomena become more obvious with increasing electrolyzing time. The different thickness of copper deposits on different substrate, such as 55μm on copper substrate in Cu(BF₄)₂-[bmim]BF₄ system while 199μm on stainless steel in CuSO₄-H₂O-[bmim]BF₄ system, was observed. It was found that the morphologies of copper deposits can be changed and the grain can be refined by addition of [bmim]BF₄ for copper electrodeposition in CuSO₄-H₂O system at 60℃. The obvious grain refining was observed at 5%(v/v)of [bmim]BF₄.