Effect of polyanion precursors on the rate of electrodeposition of hydrated tungsten oxide

Abstract

A quantitative study of the composition of metastable acidic tungstate-vanadate solutions was carried out. The main polyanions coexisting in the solutions were determined by means of UV spectroscopy. Effect of the initial V: W ratio on the nature and concentration of polyanions was determined. Electrochemical deposition of hydrated tungsten oxide films from mixed solutions was carried out. The addition of 5–30 mol.% of vanadium leads to a significant increase in the deposition rate, and these rates are higher than in analogous solutions with the addition of H₂O₂. It is shown, that the growth of films in mixed solutions is associated with the formation of the Lindquist polyanions [VW₅O₁₉]³⁻ and [V₂W₄O₁₉]⁴⁻ with high redox potentials. These polyanions are irreversibly destroyed upon reduction. The influence of various polyanions on the film growth was demonstrated in test experiments on the deposition from solutions prepared from individual salts of the polyanions. Films deposited from mixed tungstate-vanadate solutions contain a very low amount of vanadium as it was shown by elemental analysis.