Marco F. Suárez-Herrera

Electrochemical properties of thin films of polythiophene polymerized on Basal plane platinum electrodes in nonaqueous media.

In this paper the electrochemical properties of polythiophene thin films synthesized on single-crystal platinum electrodes are studied. It was found that the electrochemical properties, ion transport kinetics, and morphology of the polythiophene films depend on the surface orientation of the single-crystal platinum electrode used for their electropolymerization. Different oxidation levels, regarded as neutral, polaron, bipolaron, and metallic states, are usually found in conjugated heterocyclic polymers. However, the transitions between the different oxidation levels were never clearly observed in cyclic voltammetry. Instead the voltammograms usually show broad oxidation and reduction peaks with some shoulders. With the use of single-crystal platinum electrodes, it was found that polythiophene has a well-defined redox process at low potential, not observed before, possibly related to the conversion from the neutral state to polarons. On the other hand, two well-defined consecutive steps were found during the ion exchange reaction of thin films of polymer, both characterized by nucleation kinetics. This is the first report of two consecutive nucleation processes during the ion exchange process of a conducting polymer. The results presented here could further illuminate the mechanism in which the electron is transported in organic semiconductor materials.

Voltammetry of Basal Plane Platinum Electrodes in Acetonitrile Electrolytes: Effect of the Presence of Water

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.

Electrochemical properties of poly(3,4-ethylenedioxythiophene) grown on Pt(111) in imidazolium ionic liquids

Poly(3,4-ethylenedioxythiophene) (PEDOT) was galvanostatically synthesized and studied on a Pt(111) electrode in the following ionic liquids: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf2]), 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([Emmim][NTf2]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][OTf]) and 1-butyl-2,3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmmim][NTf2]) by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The thin films prepared with this method and cycled in these ionic liquids show high n-doping currents and high rates of ion exchange during redox switching compared to those obtained in molecular solvents.

IR and electrochemical synthesis and characterization of thin films of PEDOT grown on platinum single crystal electrodes in [EMMIM]Tf2N ionic liquid.

Summary Thin films of PEDOT synthesized on platinum single electrodes in contact with the ionic liquid 1-ethyl-2,3-dimethylimidazolium triflimide ([EMMIM]Tf2N) were studied by cyclic voltammetry, chronoamperometry, infrared spectroscopy and atomic force microscopy. It was found that the polymer grows faster on Pt(111) than on Pt(110) or Pt(100) and that the redox reactions associated with the PEDOT p-doping process are much more reversible in [EMMIM]Tf2N than in acetonitrile. Finally, the ion exchange and charge carriers’ formation during the p-doping reaction of PEDOT were studied using in situ FTIR spectroscopy.

Effect of carbon tetrachloride on the luminol sonochemiluminescence reaction kinetics during multibubble cavitation

The sonochemiluminescence (SCL) of luminol reaction was studied in alkaline medium using a dissolution of luminol, sodium carbonate, hydrogen peroxide and carbon tetrachloride. The presence of carbon tetrachloride enhances the SCL reaction up to allow the study of the reaction in real time using a cell phone video camera. This experimental setup allows the study of the cavitation dynamics in real time and through all the reactor, including homogeneous and heterogeneous cavitation zones. Finally, it was tested the effect of ethanol, the ionic strength and pH on the SCL.