Electrochemical behavior of vanadium-substituted Keggin-type polyoxometalates in aqueous solution

Cyclic voltammetry was carried out on selected vanadium-substituted Keggin polyoxometalates in aqueous solution with a focus on K₃H₂[α-SiVW₁₁O₄₀] · 6H₂O (SiVW₁₁O₄₀) and K₄H₂[γ(1, 2)-SiV₂W₁₀O₄₀] · 4H₂O (SiV₂W₁₀O₄₀). The redox waves of the V-O and W-O framework for both polyanions are pH- and scan rate-dependent. The first vanadium-centered wave (V-wave) for SiVW₁₁O₄₀ shows a classical potential shift as a function of acidity at pH < 3.5, and then becomes pH-independent above this value. Above pH 3.5, the W-centers in SiVW₁₁O₄₀ and SiV₂W₁₀O₄₀ exhibit efficient electrocatalytic activity towards the reduction of nitrite and hydrogen peroxide while the V-waves also exhibit an electrocatalytic response in nitrite-containing solutions.