Fig. 1a shows the first voltammogra

Fig. 1a shows the first voltammogram recorded on a freshly polished stationary vitreous carbon electrode in three sulfate solutions, respectively containing only Cu2+ ions, only Rh3+ ions, or both Cu2+ and Rh3+ ions.The Cu2+ reduction peak was located at −0.10 V, and the Cu stripping peak at 0.20 V, close to the formal potential of the Cu2+/Cu couple. The potential of the Rh3+ reduction peak was −0.48 V, about 1 V more negative than the formal potential of the Rh3+/Rh couple,possibly due to complex kinetics (see [13] and references therein).