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

The kinetics of zinc deposition from a concentrated chloride electrolyte co ntaining 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 t he elementary steps involved in the crystal growth process. Simulation of t he electrode kinetics shows that the additive modifies the deposit morpholo gy by changing some specific rates of the surface steps: slowing down the c harge transfer reactions, poisoning the active kink sites and increasing th e deposition overpotential. Thus zinc deposition takes place on a surface w here the intermediate adions Zn-ad(+) and the active kink sites are more nu merous and where the nucleation rate is increased, leading to refined grain size.