The electrocrystallization of cobalt-copper alloy on the glass carbon electrode from Co rich sulfate solutions was studied by utilizing electrochemical techniques of cyclic voltammetry (CV) and chronoamperometry (CA), coupled with the scanning electronic microscopy (SEM) and the energy dispersive X-ray (EDX) analysis. EDX results indicated that the nuclei formed were Co-rich Co-Cu alloy. Analysis of the current-time transients by the chronoamperometry and SEM images indicated that the nucleation mechanism of Co-Cu alloy from the sulfate solution occurred by the instantaneous nucleation with the three-dimensional growth under the diffusion control. Furthermore, with the increase of the copper ion concentration in the bath, the nucleation and growth rate improved. (c) 2007 Elsevier Ltd. All rights reserved.