Electrochemical characterization of glassy carbon electrodes modified with hybrid inorganic-organic single-layer of α-Keggin type polyoxotungstates

It has been demonstrated, for the first time, that an adsorbed single-layer of the hybrid salts (TBA)₄H₃PW₁₁O₃₉, (TBA)₄PW₁₁Fe(H₂O)O₃₉, (TBA)₄PW₁₁Mn(H₂O)O₃₉ and (TBA)₄HPW₁₁Co(H₂O)O₃₉ can be fabricated on the surface of a glassy carbon electrode by the droplet evaporation methodology. These chemically modified electrodes were stable and their preparation was reproducible and easy to perform. The electrochemical features of the immobilized polyanions were different from those of the corresponding soluble species, namely in what concerns the peak potential values. The effect of the scan rate and of pH on the voltammetric features led to the conclusion that the first W reduction process for all immobilized polyanions was diffusion-controlled. For TBA-PW₁₁, TBA-PW₁₁Fe and TBA-PW₁₁Co the two-electron reductions at the first W waves are accompanied by the uptake of protons (2 H⁺ for the PW₁₁ anion and 4 H⁺ for the Fe-substituted and Co-substituted species). For the PW₁₁Mn-modified electrode, the reduction at the first W wave was a 1 e/2 H⁺ process. Additionally, the results obtained in the presence of Na₂SO₄ in the solution highlighted the role of the ions in the supporting electrolyte in the redox features of the immobilized hybrid phosphotungstates.