Theoretical and Experimental Cyclic Voltammetry Studies of the Initial Stages of Electrocrystallization

The problem of the cyclic voltammetry investigation of the initial stages of electrochemical phase formation is considered. Analytical expressions are derived for the cyclic voltammograms and the sizes of the independent new-phase nuclei having formed on an indifferent electrode under linear potential sweep conditions for the cases of instantaneous and progressive nucleation followed by diffusion-controlled growth. The current as a function of the overpotential is found to have different dependences on the scan rate for the given limiting cases of nucleation. The results of a numerical simulation are presented. The logarithmic dependences of the maximum and minimum currents on the scan rate are shown to have a slope of –1/2 if nuclei appear in a narrow time interval long before the reverse, their number does not change when the scan rate changes, and their growth is controlled by diffusion. The slope of the dependences is –3/2 when nuclei form before and after the reverse and their number decreases with increasing scan rate. The possibility of using the proposed criteria for the interpretation of the experimental cyclic voltammograms is analyzed and confirmed for the model system (KNO3–NaNO3–AgNO3 melt/iridium substrate/silver) at low concentrations of depositing ions, which provide diffusion control of the process. Both instantaneous nucleation and progressive nucleation are shown to occur in this system, depending on other experimental conditions.