Cathodic Processes in Cu(II) Solutions Containing Glycolic Acid

Voltammetric data for Cu|Cu(II), glycolic acid system, obtained at pH < 4 under potential sweep conditions, is analyzed within a theoretical model describing the mass transport of chemically interacting particles. Accounting for the distribution of the system's components at the electrode surface makes it possible to construct linear Tafel plots normalized to the surface concentration of Cu²⁺ ions, which are treated as electrically active aqua-complexes. The rate of Cu(II) reduction involving two consecutive reactions (Cu²⁺ + e Cu⁺ and Cu⁺ + e Cu) is controlled by the transfer of the first electron with kinetic parameters _c1 = 0.27 ± 0.01 and k _s1 = (1.2 ± 0.2) × 10^–3 cm/s. Another cathodic reaction is observed at higher cathodic polarizations. Well-defined current peaks located at ca. –0.9 V (SHE) increase with both H⁺ and ligand concentration. This process presumably results from the reduction of hydronium ions involving glycolic acid as a labile donor of protons.