Electrochemical impedance spectroscopy and electron spin resonance characterization of the conductive state of parasexiphenylene electrochemically intercalated with sodium.

The electrochemical intercalation of sodium ions into parasexiphenylene (PSP) was studied by electron spin resonance (ESR) and electrochemical impedance spectroscopy (EIS). These complementary techniques give informations about the conduction state of the host material as a function of the doping rate both in the intercalation and deintercalation processes. These data were compared to the previous works concerning the intercalation of alkaline ions into polyparaphenylene (PPP).

Raman spectroelectrochemical study of sodium intercalation into poly(p-phenylene).

The structural defects formed along the polymer chain during the electrochemical intercalation of sodium into polyparaphenylene (PPP) were investigated by in situ FT Raman measurements with an excitation wavelength of 1064 nm. Our Raman data are compared with those obtained for PPP and its oligomers intercalated with Na(+) ions by chemical ways. The coexistence of polarons and bipolarons is observed in the early stages of the intercalation process. When the doping level increases polarons are transformed to bipolarons, then in the highly intercalated sample (corresponding to a composition close to Na(0.5)(C(6)H(4))), bipolarons are the main structural defects. This evolution, which is reversible, is in accordance with the electron spin resonance (ESR) data of PPP intercalated with sodium ions in the same experimental conditions.

Electrochemical properties and Fourier transform-infrared spectroscopic investigations of the redox behaviour of poly(indole-5-carboxylic acid) in LiClO4-acetonitrile solutions.

Electropolymerisation of indole-5-carboxylic-acid leads to the formation of electroactive polymer films. Potentiostatic deposition of the related polymer, poly(indole-5-carboxylic-acid), was carried out at a constant potential at 1.35 V versus SCE. The cyclic voltammogram of the resulting polymer in LiClO4 (0.15 mol dm(-3))/acetonitrile solution is characterized by two poorly resolved anodic and cathodic set peaks. FTIR spectroscopy was used to characterize both reduced and oxidized forms of poly(indole-5-carboxylic-acid). Assignments of the vibrational modes were proposed by comparison of the vibrational spectra of polyindole and polycyanoindole. The polymerization sites correspond to the 2 and 3 carbon positions of the pyrrole cycle. In the oxidized form of the polymer, the NH group is deprotonated while the quinoid form is present between the pyrrole rings.

In-situ spectroscopic investigations of the redox behavior of poly(indole-5-carboxylic-acid) modified electrodes in acidic aqueous solutions.

The oxidation of electrochemically grown poly(indole-5-carboxylic-acid) (P5CO2H) and its spectroscopic properties have been studied by in-situ spectroelectrochemical techniques. The purpose of this paper is to characterize the different modifications on the P5CO2H backbone, induced by the electrochemical oxidation in aqueous acidic solution. We have identified, on the basis of Raman spectra, the vibrational modes associated with neutral and oxidized segments of polymer. It was shown that at least three chemically and optically different species (perhaps other products too) are produced in different potential regimes upon oxidation of this polymer. The results obtained also indicate that the molecular properties of this conducting polymer are better revealed by in-situ resonant spectra than by ex-situ infrared and Raman studies.

UV-vis and Raman spectroelectrochemical investigation of the redox behavior of poly(5-cyanoindole) in acidic aqueous solutions.

Spectroelectrochemical properties of conducting poly(5-cyanoindole) films deposited on indium tin oxide (ITO) and platinum electrodes are investigated using UV-vis and resonant Raman spectroscopies. The transitions from undoped to semi-conducting state of P5CN require the partial oxidation of the polymer to create radical-cations by insertion of charge-neutralizing anions into the polymer. In order to obtain detailed structural information from the vibrational spectra, it is necessary to know the vibrational modes of oxidation-sensitive bands. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The drastic changes in optical absorption and Raman spectra observed at various stage of oxidation were explained by the conversions between at least three different structures. On the basis of the Raman spectra, we have identified the vibrational modes associated with neutral and polaronic segments. The perturbation associated with the coexistence of these polaronic segments has been described as a quinoid structure growing on the expense of the benzoid one. The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in-situ Raman spectra than by ex-situ studies.

Identification by TEM and EELS of the products formed at the surface of a carbon electrode during its reduction in MClO4-EC and MBF4-EC electrolytes (M = Li, Na)

The electrochemical intercalation of lithium and sodium into graphite was carried out using a liquid electrolyte containing ethylene carbonate (EC) as solvent and MClO4 or MBF4 (M = Li, Na) as salts. The first intercalation of alkali metals into graphite is accompanied with irreversible reactions attributed to the reduction of the electrolyte. These reactions contribute to the development of a passivating layer, formed on graphite surface prior to intercalation. This layer is impervious to solvent molecules but allows alkali ions to diffuse through its bulk. The surface chemistry of the electrodes was characterized using transmission electron microscopy (image, selected area electron diffraction) as well as EELS. The effect of the nature of the alkali salts on the properties of the passivating layer is studied.