Kinetic Regularities of Lead Dioxide Electrocrystallization
Authors: Shmychkova Olesia , Luk'yanenko Tatiana , Velichenko Alexander 
Published: February 2020

Lead dioxide is a promising anodic material owing to corrosive resistivity, low cost and high electrocatalytic activity. Lead dioxide is extensively employed in electroplating, hydrometallurgy, processes of electrosynthesis of strong oxidative agents, organic and inorganic compounds, in reactions of the electrochemical combustion of various organic pollutants (1–3).
Establishing of kinetic regularities of the crystallization process and control of its parameters is very important, because determines basic properties of the resulting materials. In the present work we examine early stages of electrocrystallization of PbO2 from methanesulfonate/nitrate electrolytes.
Electrodeposition regularities of lead dioxide both in nitrate and methanesulfonate electrolytes were studied on Pt disk electrode by steady-state voltammetry, chronoamperometry. Voltammetry measurements were carried out in a standard temperature-controlled three-electrode cell. All potentials were recorded and reported vs. Ag / AgCl / KCl (sat.).
Current transients for PbO2 deposition on Pt disk electrode were obtained for investigation of initial stages lead dioxide electrodeposition (Fig.). The type of transient is determined by the electrode potential. At low polarizations (E=1550 mV) the biggest induction period with a further stretched maximum of current is observed. Increasing of an anodic polarization leads to a substantial decreasing of the induction period and to increasing of current maximum. Such type of transients indicates difficulties in initial stages of nucleation and confirms that the process is controlled by the kinetic stage.
The electrocrystallization model, proposed by Abyaneh (4), was selected as appropriate for investigation of initial stages of the formation of a new phase of lead dioxide. In the formation of oxide coatings three basic nuclei geometries such as semi-spheroid, cone and cylinder are considered.
Depending on the composition of electrolyte may occur either the predominance of one phase over another or ingesting of growing centres of one phase by another. The formation of one phase is noticeably lagged behind the other. The type of lagging phase depends on the deposition conditions: at low polarizations there is a slight predominance of the growth of α-phase of PbO2; at high polarization α-phase becomes stunted, and there is overlap and ingesting of formed α-phase growth centers by β-phase crystals on the surface of the electrode (5).
In all cases, the type of nucleation is progressive. However, the preferred form of crystals at 2D nucleation in the case of methanesulfonate electrolyte is the cylinder, and in the nitrate electrolyte the crystal formation occurs in the form of cones, that is in accordance with scanning electron microscopy results.
The electrocrystallisation of PbO2 begins with the formation of a monolayer, and only then there is the formation and growth of 3D nuclei, so each consequent layer is formed on the renewed surface (5).
The increase of CH3SO3
- ions in the deposition electrolyte leads to significant reduction in the induction period, that indicates the facilitation of initial stages of phase formation of lead dioxide, and also causes a noticeably increase of the deposition current. This effect of changing of kinetic parameters of 2D nucleation of lead dioxide probably will affect the 3D crystallization of the coating and as a consequence the phase composition of the coating. Thus, in the deposit obtained from the nitrate electrolyte the content of β-phase is much higher, than in the case of a coating, obtained from an electrolyte based on methanesulfonic acid. The character and kinetic parameters of 2D nucleation of lead dioxide crystals allows predicting the phase composition of coatings.
With the angular velocity growth the induction period significantly changes. Increasing of the angular velosity should promote the growth rate of accumulation of PbO2 in the surface layer and thereby lead to a reduction of time required for the nucleation. In comparison with perchlorate and nitrate electrolytes (6) in methanesulfonate deposition electrolyte the effect of current reducing with increasing of angular velocity of the electrode at low potential is less pronounced probably due to a more significant interaction of Pb(III) intermediate product with the electrode surface.

References

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Figure 1