Portugaliae
Electrochimica Acta

The use of in situ infrared (IR) vibrational spectroscopy on the elucidation at a molecular level of electrochemically induced phenomena, i.e., in situ IR spectroelectrochemistry, has been rapidly developing in the last two decades, since a pioneer work of Bewick et al., by using modulation and synchronous detection of the signal in external reflectance IR spectroscopy. In situ IR spectroelectrochemistry has been proved to be a powerful tool for investigation of the electrode solution interface, namely by providing information on the structural, bonding and dynamical properties of adsorbate species on electrode surfaces, on the behaviour of supporting electrolyte and solvent molecules at the electrochemical interface and also on reaction mechanisms and kinetics of electrocatalytic reactions. An overview of some theoretical aspects of IR reflectance spectroscopy is presented and experimental details of some in situ techniques are described, namely EMIRS (Electrochemically Modulated Infrared Reflectance Spectroscopy), SNIFTIRS (Subtractively Normalised Interfacial Fourier Transform Infrared Reflectance Spectroscopy) and SPAIRS (Single Potential Alteration Infrared Reflectance Spectroscopy). A few selected applications of these techniques to electrocatalysis are also presented.

The polarographic and voltammetric reduction of dithizone (1, 5-diphenylthiocarbazon, H2Dz, thiol form I) has been studied in Britton-Robinson buffers (pH 2.10-12.00) containing 50% ethanol at room temperature. The reduction of the compound takes place in single 2e- transfer, giving a diffusion controlled reversible wave in the entire pH range of the study corresponding to the reduction of the azo group. A mechanism is proposed for the reduction process of the compound.

Increased interest in highly conducting polymer electrolytes is clearly evident from the open literature, particularly on the specific area of energy-related applications. Poly(ethylene oxide), PEO, although well studied, continues to intrigue us and must still be regarded as playing a central role in polymer electrolyte research and development. Ion containing organic polymers involving essentially PEO as the solvent matrix are reviewed here. The greatest technological driving force for its continued study is still, by far, the desire for thin film rechargeable batteries that meet a multitude of ambitious energy, power density and safety requirements, while not being prohibitively expensive.

Using square- wave voltammetry at a static mercury drop electrode, a fast and simple method has been developed for the assay of the water-soluble vitaniins tliiamiiie hydrochloride, riboflavin, folic acid and nicotinamide. In Britton Robinson buffer (pll 9.5) by cathodic scan thiamine hydrochloride give a peak at -1.33 V, riboflavin give two peaks at -0.61 V and -0.73 V, folic acid gives a peak at -0.91V and nicotinamide give a peak at -1.74 V vs. Ag/AgCl reference electrode at the same buffer solution. These four vitamins can be determined by the same voltammogram. The reduction peak currents are linearly dependent on the concentration of the vitamins. The method is successfully applied to determine these four vitamins contents of multivitamin preparations simultaneously. The values found agreed well with those determined by other methods.

The electrochemical behaviour of the cyanometalate complexes [Fe(CN)e]4" [W(CN)8]4\ [Os(CN)6]4-, [Mo(CN)8]4" and [Ru(CN)6]4" is investigated at high concentrations of the corresponding potassium salts (0.6 M) in alkaline solution (pH = 13) by voltammetric measurements with a platinum microdisk electrode. Under these experimental conditions the electrode reactions are reversible and the half-wave potentials are about 130 mV more positive than the standard redox potentials of these couples. The analytical characteristics of voltammetric determinations at high concentrations of electroactive species are studied using K4[W(CN)g] as a model compound.