It is recognized that electrodeposition of lead dioxide from different oxide particle suspensions leads to composite materials that notably differ from pure PbO₂ composition in terms of physico-chemical properties and electrocatalytic activity (1-3).

It appears that the deposition and formation of composite materials is also influenced by the nature of the dispersed phase, the time stability of the resulting suspension and the use of additives in the electrolytes (4, 5). Stirring of the deposition electrolyte has a significant influence as it helps to maintain the particles in suspension and favors their transportation to the electrode surface. It has been shown that increasing the mixing velocity results in an increase of the dispersed phase in the coating. However, the issue of the directed synthesis of these materials is still open since some details concerning the effect of various factors on the composition and physico-chemical properties of the coatings remain to be investigated.

Herein, we report the effect of deposition conditions on the composition, physico-chemical properties of composite PbO₂-TiO₂ materials obtained from methanesulfonate electrolytes containing nanosized TiO₂ particles as the dispersed.

The surface morphology and chemical composition of obtained materials were investigated by SEM, EDAX, phase composition and texture was determined by X-Ray powder diffraction.

Composites comprising TiO₂ nanoparticle in PbO₂ matrices can be formed by electrodeposition. These particles are delivered from the electrolyte bulk to the electrode surface by diffusion and/or migration (as a result of the appearance of partial concentration gradient in a colloidal solution due to the depletion of particles, included in the growing coating, in near-electrode zone). The content of the composite material depends on i) the electrolysis conditions; ii) surface charge of the dispersed phase particles and of the electrode; iii) the PbO₂deposition rate; iv) the concentration of components in the solution. By varying the electrolysis regimes and the composition of the electrolyte, composites containing from 4 to 27 wt.%. TiO₂ can be synthesized. The phase composition and texture of the resulting composites depend on the electrolysis conditions and the composition of the electrolyte. Thus, the presence of TiO₂ particles in the electrolyte leads, as a rule, to decrease of the crystal size and growth of the content of α-phase of lead dioxide in the deposit. The content of the PbO₂ α-phase depends on the TiO₂ concentration in the suspension electrolyte and has a maximum at 1.0 g dm^-3 TiO₂. The texture differs substantially from both deposits obtained from a true solution and from those prepared from electrolytes with a high content of disperse particles. In the latter case, the degree of crystallinity of the coatings increases, as evidenced by the increase of the peaks intensity and sharpness on diffractogramms.

The phase composition and texture of composite coatings as well as their TiO₂ content are markedly affected by raising the concentration of dispersed particles and the current density because this increases the number of nucleation sites by facilitating TiO₂ transport to the electrode surface by diffusion or migration. The data suggest that the presence of nucleation sites on the dispersed phase particles, both on the electrode surface and in the near-electrode area, facilitates the crystallization of PbO₂ α-phase. It should be pointed out that a significant increase in the number of particles leads to the surface shielding; causing polarization and accelerating of the β-phase. This explains the extreme dependence of the phase composition of lead dioxide on the content of the dispersed phase particles in the suspension electrolyte. The lack of TiO₂ peaks on X-ray diffraction patterns is likely due to nanoscale of dispersed phase particles in composite materials based on lead dioxide.

References

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