Comparative study of nucleation and growth mechanism of cobalt electrodeposited on ITO substrate in nitrate and chloride electrolytes

A comparative study of the electrochemical deposition of cobalt on tin-doped indium oxide (ITO) substrate was carried out using electrochemical techniques in nitrate and chloride electrolytes. The bath used for the study in a nitrate medium contains 0.01 M of cobalt nitrate hexahydrate (Co(NO3)(2). 6H(2)O) with 0.1 M of potassium nitrate (KNO3). For the chloride medium study, the electrolyte consists of a mixture of 0.01 M CoCl2 with 0.1 M potassium chloride (KCl). The cyclic voltammetry (CV) and the chronoamperometry (CA) have been used to study the kinetics, nucleation, and growth mechanism. The (CV) and (CA) measurements revealed that the electrodeposition of cobalt (Co) at a negative potential around -0.95 V versus SCE (saturated calomel electrode) is a quasi-reversible reaction controlled by the diffusion process in the two electrolytes. The measured current transient curves were compared to those calculated from Scharifker-Hills and Heerman-Tarallo models. It was found that a progressive three-dimensional (3D) nucleation mechanism governed the nucleation and the growth of Co on the ITO substrate in chloride solution, while in nitrate solution, the nucleation mechanism followed the instantaneous 3D model. The characterization of samples by X-ray diffraction had shown that the cobalt electrodeposited on ITO substrate has a hexagonal crystal structure whatever the electrolyte composition.