RESUMEN
The first part of this communication studies the electrochemical properties of thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) grown on the three basal plane platinum electrodes via cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy and in situ FTIR spectroelectrochemistry. In the second part of this work the redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at these platinum modified electrodes is investigated via cyclic voltammetry and electrochemical impedance spectroscopy in order to elucidate the effect of some polymer properties on its electrocatalytic behavior, such as the ionic resistance, nature of the doping ion and the structure. First of all, it was found that the ionic resistance of the PEDOT films electrochemically synthesized on platinum electrodes increases in the order Pt(100) < Pt(110) < Pt(111) and the advantages of using single crystal platinum electrodes coated with PEDOT for the IR study of individual mobile species flux and the evolution of charge carriers during the reduction process of p-doped PEDOT were proven. On the other hand, it was found that compact, rigid and low resistance PEDOT films show higher standard charge transfer rates for the DMcT redox reaction than those that have a more porous structure and higher ionic resistance. Finally, PEDOT films doped with alkaline ions are more electrocatalytic for the oxidation process of the protonated form of DMcT.
RESUMEN
The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.