The effect of different electrolytes (ClO4-, NO3-, and SO42- at 1 M) at pH 3 on the kinetics, growth type, and morphology of copper electrodeposition on glassy carbon was studied. The concentration was 0.1 M Cu2+ in all of the solutions employed. In cyclic voltammetry, a larger reduction peak was obtained in the nitrate electrolyte, in comparison with the other two media. This higher current has been associated with the catalytic reduction of nitrate ions on recently deposited metallic copper. This effect was confirmed in the potential-step analysis. Despite the fact that Cu+ is not thermodynamically stable in these three solutions, the reduction step Cu2+/Cu+ has been considered as an electron-transfer reaction. The anion type has a direct effect on this electron-transfer reaction and consequently, on the electrocrystallization process; sulfates provoke the most important current decrease associated with the Cu2+/Cu+ step and also strongly influence the nuclei formation, while the nitrate ions accelerate the Cu2+/Cu+ step. The scanning electron microscopy images obtained for copper deposits after different deposition times corroborate the type of copper nucleation predicted by the electrochemical techniques. (c) 2007 The Electrochemical Society.