Properties of 1-n-butyl-3-methylimidazolium bromide-copper (II) bromide ionic liquid as electrolyte for electrochemical deposition of copper

Physicochemical properties of 1-n-butyl-3-methylimidazolium bromide-copper (II) bromide ionic liquid (BMImBr-CuBr2) were studied with conductometric, densimetric, and viscometric methods. It was shown that the conductivity decreased from 0.386 to 0.275 S cm− 1 with CuBr2 concentration increasing from 0 to 2.0 mol kg− 1 at 333 K. With increasing of CuBr2 content the density rose gradually but a minimum was observed on viscosity concentration dependence. The interaction of BMImBr and CuBr2, resulting in the formation of a complex anion, was confirmed by the dependence of both the conductivity temperature coefficient and the effective activation energy of conductivity on the salt concentration. It was found that in BMImBr-CuBr2 mixture Cu(II) reduced to Cu(0) on tantalum and titanium electrodes by two one-electron stages. Moreover it was established that high quality copper coatings on tantalum and titanium electrodes could be formed only within the potential range Ec = −(1.8-2.0) V (vs. Pt), which corresponded to the rising branch of the second current peak on the cathodic polarization curve. High adhesion of copper coating on tantalum and titanium substrates could be achieved only after vacuum annealing at 473 K. The annealing was not required in the presence of F− anion.