A new insight into the mechanism of lead electrodeposition: Ohmic-diffusion control of the electrodeposition process

A new insight into the mechanism of lead electrodeposition from nitrate solutions is presented by analysis of the polarization characteristics and by scanning electron microscopic (SEM) analysis of the surface morphology of the lead deposits obtained in the potentiostatic regime of electrolysis. In dependence on the concentration of Pb(II) ions, the electrodeposition process is either mixed ohmic-diffusion or completely ohmic controlled. The ratio of the ohmic control to the total control of the electrodeposition process increased with increasing concentration of Pb(II) ions and at the higher concentrations of Pb(II) ions, the electrodeposition process became completely ohmic controlled. The polarization characteristics were well correlated with the morphologies of the obtained lead deposits. The formation of regular crystals was a characteristic of ohmic control of the electrodeposition process, while needle-like and fern-like dendrites were the predominant morphological forms obtained under diffusion control. The critical overpotentials for both dendritic growth initiation and instantaneous dendritic growth were analyzed and a mechanism of lead electrodeposition based on this analysis is presented. It was shown that the values of these critical overpotentials decreased and approached one another with increasing concentration of Pb(II) ions and finally became the same when full ohmic control was attained. The presented results were in good agreement with the predications of the general theory for the formation of disperse metal electrodeposits.