Impedance of copper electrode in acid Cu(II) solutions containing gluconic acid

Electrochemical impedance spectroscopy was applied to study the processes taking place on the Cu electrode in 0.01 M Cu(II) solutions containing 0.04 M gluconic acid and 0.3 M K(2)SO(4) (pH 3.0). The Nyquist plots obtained under open-circuit and cathodic polarization conditions present the arcs centred below the abscissa axis. The description code of the adequate equivalent circuit is R(Omega) (C(dl)[R(1)W(1)] [R(2)W(2)]) (here, elements in series are written in angle brackets and parallel elements are given in parentheses). The settled exchange current densities obtained for the two-step charge transfer process (i(01) = 4.8 mu A cm(-2) and i(02) = 440 mu A cm(-2)) are in good agreement with the quantities obtained earlier from voltammetric data. The double-layer admittance was found to increase with the cathodic overvoltage approaching the values that are typical of additive-free Cu(II) solutions. Desorption of gluconate is supposed to occur at potentials adjacent to the plateau of the limiting current.