Electrodeposition of Copper from Cupric Pyrophosphate Solutions

Abstract

Cathodic current-potential curves were obtained for copper in cupric pyrophosphate solutions by using a rotating disk type electrode, where the effect of concentration polarizations was completely eliminated. For all solutions tested (Table 2), Tafel relations having a slope b of about -0.5V were observed in the potential region of -0.75~-IV vs. SCE (Figs. 6 and 7). The exchange current densities i0 for the copper deposition reaction were obtained by extrapolating the Tafel lines to the rest potentials which are considered to be the equilibrium potentials for the reaction (Table 3). It was found that i0 increases with increasing concentration of Cu(P2O7)26- ion but decreases with the increase of P2074- ion concentration for small concentrations of this ion (Figs. 10 and 11). From the results of experiments, the following mechanism was proposed in which CuP2O72-, produced by the dissociation of Cu(P2O7)26-, is directly taking part in the electrode reaction. Semibright deposits were always obtained when the potential is more positive than -0.75 V vs. SCE and the current is larger than about i1 of 5 mA/cm (Fig. 8). The value of the current i2 corresponding to the critical potential of -0.75 V increases with increasing concentration of P2O74-. In the range of i1~i2, electrode surface is considered to be weakly adsorbed with pyrophosphate ions which allow random or smooth deposition of metal atoms. © 1974, The Chemical Society of Japan. All rights reserved.