Chronopotentiometry and linear potential sweep (LPS) voltammetry were applied to study cathodic processes occurring at the Cu electrode in Cu(II) solutions containing gluconate (L-) and excess of sulfate at 2 < pH <5. The data obtained are indicative of sufficiently high lability of both CuL+ and CuSO4 complexes. The effective diffusion coefficients obtained from transition times (tau) are in the range from 4.4 x 10(-6) to 3.7 x 10(-6) cm(2) s(-1) and decrease with the molar fraction of CuL+. No adsorbed electrochemically active complexes (EAC) were detected. Additional tau' observed at pH 5 results from the reduction of surface Cu2O that is formed at the open-circuit potential. LPS voltammograms contain two current maxima conditioned by Cu(II) and H3O+ reduction, respectively. The first of them contains irregularities that disappear when perchlorate is substituted for sulfate. Cu2+ aqua-ions take part in the consecutive transfer of two electrons whereas CuL+ complexes seem to be electrochemically inert. Cathodic charge transfer coefficients (alpha =0.43 +/- 0.03), determined by different methods, correlate well. A role of adsorption processes has also been discussed. (C) 2012 Elsevier Ltd. All rights reserved.