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)(4)H3PW11O39, (TBA)(4)PW11Fe(H2O)O-39, (TBA)(4)PW11Mn(H2O)O-39 and (TBA)(4)HPW11Co(H2O)O-39 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.