The electrodeposition of metals is a complex phenomenon influenced by a number of factors that modify the rates of nucleation and growthand determine the properties of the deposits. In this work we study the influence of the zinc chloride (ZnCl2) concentration on the zinc nucleation process on glassy carbon, in a KC1 electrolyte under conditions close to those employed in commercial acid deposition baths for zinc. The electrochemical study was performed using cyclic voltammetry and potentiostatic current-time transients. The charge-transfer coefficient and the formal potential for ZnCl2 reduction were evaluated from cyclic voltammetry experiments. The nucleation process was analyzed by comparing the transients obtained with the known dimensionless (/m)2 VS. t/tm reponse for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl2 concentration. Scanning electron microscopy analysis of the deposits shows that the deposits are homogeneous and compact although a change in the morphology is observed as a function of ZnCl2 concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits. InfroductionElectrodeposition of zinc and its alloys has been widely implemented as a corrosion resistant coating on steel. The coating cathodically protects the steel from the environment. Considerable research has been conducted on the factors affecting the quality of the electrodeposits, e.g., crystallographic orientation, nature of the substrate, additives, composition, etc.3 For the electroplating of zinc on glassy carbon at low overpotentials from solutions containing 3 M ZnC12 or 3 M ZnBr2, McBreen and Gannon4 showed that the nucleation overpotential is smaller for ZnCl2 than for ZnBr2 solution probably due to the lower stability constant of ZnBr2. In both systems nucleation was. observed to proceed instantaneously with subsequent growth being controlled by diffusion. In another study the nucleation rate and number density of active sites for zinc electrodeposition from zinc chloride in a sodium chloride supported electrolyte was found to increase with chloride concentration.5 * Electrochemical Society Active Member.