Cathodic processes in solutions containing Cu(II) tartrate complexes

Cathodic processes occurring in the solutions containing Cu(II) tartaric complexes have been investigated. The equations accounting for the material balance have been constructed and used for the estimation of distribution of complexes and ligands in the bulk of solution. It was established that dominating particles in acidic media (pH < 3) are: Cu2+ and tartaric complex CuL, tartaric acid LH2 and its anion LH-. Potentials of non-polarized copper electrodes were found to be reversible and to follow Nernst equation. According to the analysis performed, surface oxide Cu2O is not able to form in acidic (pH < 3) media. Cathodic voltammograms obtained for the solutions of different acidity exhibit two characteristic current peaks arising from Cu(II) reduction and hydrogen evaluation. An analysis of voltammetric extrema shows that both processes are irreversible. Based on the regularities of the mass transport of chemically interacting substances, surface distribution of components has been simulated. These date were used for the transformation of experimental voltammograms into normalized Tafel plots. According to their analysis, the rate-controlling step of Cu(II) reduction is the transfer of the first electron onto Cu2+ aqua-complex. The values of kinetic parameters were found to be as follows: the cathodic charge transfer coefficient is equal to 0.33 and the exchange current density is equal to 50 mA cm-2. An analysis of the second current peak leads to the conclusion according to which the H3O+ reduction is coupled with chemical reactions involving protonated forms of ligand that additionally generate these ions.Švietimo akademijaVytauto Didžiojo universiteta