Electrodeposition of copper on glassy carbon electrodes in the presence of picolinic acid

The electrodeposition of copper on glassy carbon electrodes in the presence of picolinic acid (PA) was investigated by means of voltammetric, chronoamperometric and electrochemical impedance spectroscopy measurements complemented by UV-vis spectroscopy and SEM imaging. Voltammetry shows the appearance of two cathodic current peaks that are assigned to the electroreduction of copper ions and [Cu(PA)2]2+ soluble complex species. The anodic stripping of the metallic layer shows two electrochemical processes related to the formation of cupric ions that are produced from the electro-oxidation of both the deposited copper layer and the cuprous species that result from the chemical reaction between the metallic layer and cupric ions at the interface. This second contribution appears to be influenced by the initial conditions of the electrode surface and the presence of PA in solution. Voltammetry and potentiostatic current transients show that copper deposition occurs though a nucleation and growth process. From the analysis of the transients an instantaneous nucleation with 3D growth process under diffusion control is concluded, although a deviation in the curves from the model is observed. This deviation from the model, usually found in other systems, is explained in terms of the morphological characteristics of the particles depositing on the electrode surface. SEM images show the formation of nuclei on the glassy carbon surface and a change in the morphological characteristics of the deposit when the reaction occurs in the presence of PA. The Nyquist plots show a single capacitive constant at high frequencies, related to the charge transfer of copper ions, and a Warburg-type contribution at low frequencies, related to the diffusion of copper ions from the solution to the electrode surface. Values of the charge transfer resistance result lower in the presence of PA. The corresponding Bode plots show a good agreement between experimental and fitted data.