DISCHARGE AND CRYSTALLIZATION STEPS IN STEADY-STATE SILVER ELECTRODEPOSITION FROM THIOCYANATE SOLUTIONS

Steady-state silver electrodeposition was studied under galvanostatic and potentiostatic electrolysis conditions in thiocyanate solutions. T he special features of the discharge and crystallization steps in the two electrolysis modes were determined by separation of the overpotent ial distributions associated with charge transfer, crystallization, an d diffusion. At identical deposit growth rates, the crystallization ov erpotential was about 30-40% higher under galvanostatic than under pot entiostatic conditions. To the contrary, at the deposit surface grown potentiostatically, which is morphologically closer to equilibrium, th e exchange current density of the discharge step was several times low er than on the surface grown galvanostatically. The main contribution to the electrocrystallization rate is due to direct discharge at the g rowth sites. Arguments were cited for a control of silver electrodepos ition by two-dimensional nucleation.