The mechanism of cobalt electrocrystallization on fluorine-doped tin oxide (FTO)-coated conducting glass substrate has been studied and compared with results obtained on n-type Si electrodes. The initial stages of metal deposition from a solution of 0.25 M CoSO4, 1 M Na2SO4 and 0.5 M H3BO3 (pH 3.5) were investigated using cyclic voltammetry, and chronoamperometry measurements. Important kinetics parameters were estimated from the analysis of current transients on the basis of the Scharifker-Hills model for electrochemical nucleation and diffusion-controlled growth. From the analysis of the experimental current transients, it was found that the process of cobalt deposition involves a three-dimensional (3D) electrochemical nucleation and diffusion-controlled growth. A strong dependence of the number density of active sites N-0 with applied potential was observed on both FTO and n-type Si electrodes. (C) 2010 Elsevier B.V. All rights reserved.