Linear potential sweep voltammetry was applied for the investigation of cathodic processes proceeding in 0.01 M Cu(II) and 0.04 M malic acid (LH2) solutions at pH ranging from 2.2 to 4.5. The analysis of material balance in the system shows that two species containing Cu(II) are predominant in the acidic medium: CuLH⁺ at pH < 4 and CuL₂^2– at pH > 4. Fractions of other species, such as Cu²⁺, CuLH₂²⁺ and CuL, are significantly smaller. Two characteristic current peaks observed on cathodic voltammograms result from Cu(II) reduction and hydrogen evolution, respectively. It is supposed that the protonated ligands generating H⁺ ions take part in the latter process. Peak currents and potentials can be described quantitatively using equations accounting for irreversible character of both processes that are characterized by cathodic charge transfer coefficients equal to 0.4 and 0.55, respectively.

Keywords: copper, malic acid, complexes, electroreduction, potential sweep voltammetry