Impedance of copper electrode in slightly acid Cu(II)-glycine solutions

Abstract

Electrochemical impedance spectroscopy was used to study the kinetics of reduction of Cu (II) in weakly acidic (pH 4 and 5) solutions of Cu (II) containing glycine (0.04 or 0.1 M) as a complexing agent. A rather slow equilibration was observed at pH 4 and glycine concentration c_L = 0.04 M. With increasing pH or c_L, the total concentration of intermediate Cu(I) decreases. At the same time, impedance increases over the entire range of frequencies applied. An equivalent circuit with two parallel sub-circuits, each containing the charge transfer resistance and Warburg impedance in series, was used to quantify the impedance spectra. The exchange current densities of two consecutive one-electron transfers were estimated. Their average values are ~1 µA cm^–2 and ~0.1 mA cm^–2