Electrochemical nucleation and growth of cobalt onto glassy carbon electrode (GCE) from methanesulfonic acid (MSA) electrolyte was investigated, the influence of pH and cobalt concentration on the electrocrystallization mechanism was also examined. Cyclic voltammetry experiments indicate a pH and cobalt concentration dependence of the onset potential and a deposit phase change with decreasing pH was also noted. From analysis of current transients, the diffusion coefficient of cobalt ion was estimated as 1.89 x 10(-5) cm(2)s(-1). The electrocrystallization mechanism for 0.6 mol/L Co2+ follows the instantaneous nucleation with kinetic controlled growth and is independent of the bath pH while the mechanism for 0.2 mol/L Co2+ follows the progressive nucleation with diffusion controlled growth at pH = 2.0 and then goes to instantaneous nucleation with kinetic controlled growth at pH = 1.5 and exhibits a process of progressive nucleation with kinetic controlled growth with lower pH of 1.0. (C) 2018 The Electrochemical Society.