Electrochemical kinetic study about cobalt electrodeposition onto GCE and HOPG substrates from sulfate sodium solutions

In the present work, we analyze the electrodeposition of cobalt by electrochemical techniques onto GCE (system I) and HOPG (system II) electrodes from sulfate solutions. Cyclic voltammetry and current transient measurements were used to obtain the nucleation and growth mechanism. The results clearly showed that electrodeposition of cobalt is a diffusion-controlled process with a typical 3D nucleation mechanism in both substrates. The average ?G calculated for the stable nucleus formation was 1.97×10?20J nuclei?1 and 3.58×10?20J nuclei?1 for system I and system II, respectively. The scanning electron microscope (SEM) images indicated similar nucleation and growth processes on GCE and HOPG substrates at same overpotential with a homogeneous disperse cobalt clusters. X-ray energy-dispersive spectroscopy (EDS) was performed in order to ensure that the clusters formed are cobalt. The nucleis size obtained was dependent of the overpotential applied; at lower overpotentials, the growth rate of the cobalt clusters diminishes when their number increases due to the strongly reduced concentration of cobalt ions because of their consumption by a larger number of growing particles. A theoretical quantum study employing PM6 method suggests that Na+ adsorbed deactivate the local surface occasionating the formation of disperse cobalt clusters on carbon electrodes.