Impedance spectroscopy and modelling of zinc deposition in chloride electrolyte containing a commercial additive

The kinetics of zinc deposition from a concentrated chloride electrolyte containing a commercial additive are investigated by impedance spectroscopy. A reaction model formerly validated for zinc deposition in acidic sulphate medium has been adapted to the present electrolyte and closely related to the elementary steps involved in the crystal growth process. Simulation of the electrode kinetics shows that the additive modifies the deposit morphology by changing some specific rates of the surface steps: slowing down the charge transfer reactions, poisoning the active kink sites and increasing the deposition overpotential. Thus zinc deposition takes place on a surface where the intermediate adions Zn-ad(+) and the active kink sites are more numerous and where the nucleation rate is increased, leading to refined grain size.