Kinetics of cathodic processes in Cu(II) gluconate solutions containing an excess of sulfate
By Survila, A. & Kanapeckaiti, S.
Published in Electrochimica Acta
2012
Abstract
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 (Ï„) are in the range from 4.4 X 10-6 to 3.7 X 10-6 cm2 s-1 and decrease with the molar fraction of CuL+. No adsorbed electrochemically active complexes (EAC) were detected. Additional Ï„' 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 (α = 0.43 ± 0.03), determined by different methods, correlate well. A role of adsorption processes has also been discussed.