Electrodeposition Behavior of Zinc in Alkaline Zincate Electrolyte

Abstract

The cathodic reduction process of Zn in alkaline zincate electrolyte was studied by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS), while the electrochemical nucleation behavior of Zn was also characterized by using chronoam- perometry (CA) and scanning electron microscope (SEM) techniques. The results indicated that Zn existed in the electrolyte in the form of Zn(OH)4 2- , through a preceding reaction which then trans- formed into Zn(OH)2 during electrodepositing. As the species directly discharged on the cathode surface, the discharge of Zn(OH)2 is a two step-process, by the first step Zn(OH)ad was produced and adsorbed on the surface of cathode, and then was reduced to Zn by the second step. The two steps of reduction of Zn(OH)2 were all nonreversible reaction. It is beneficial to the electrodeposi- tion of Zn when the applied potential reduces. The first discharge reaction of Zn(OH)2 occurred when the applied potential was at -1.40~-1.50 V. The two discharge reactions of Zn(OH)2 were both occurred in the alkaline zincate system when applied potential reduced to -1.60 V but in this case, Zn atoms only adsorbed on the cathode surface and the electrodeposition process was in a non-steady state. The adsorbed Zn could finally electrocrystallized to form a uniform Zn coating on- ly when the applied potential reduces to -1.70~-1.80 V. The electrocrystallization of Zn from alka- line zincate electrolyte may follow a three-dimensional progressive nucleation mechanism.