Search

This article studies the synthesis and properties of copolymers of aniline and both 2-amino (2ABSA) and 3-aminobenzenesulfonic acids (3ABSA)with a molar degree of sulfonation from 3 to 33% for 3ABSA and 10 to 43% for 2ABSA. The small segments of the sulfonic species in the polymer chain (molar fraction = 0.03) confer solubility in alkaline medium (around 0.012 g L−1) and good electrochemical response at pH 7.2 improving those for the unmodified polyaniline (PANI). Taking advantage of the electroactivity at physiological pH, the electrochemical response of redox couples (ferrocyanide(II)/ferricyanide(III) and ferrocene/ferrocenium) has been analysed. The electrochemical response of Cytochrome c (Cyt c)solutions has been also studied at pH 7.2 in presence and absence of ferrocene/ferrocenium species. Ministerio de Ciencia y Tecnología (MAT2004-1479)y programa Juan de la Cierva.

In this paper we present the study of the electrochemical properties of the following conducting polymers: poly(o-anisidine), polyaniline and copolymers of aniline and o-anisidine obtained by a new synthetic method. The polymers are synthesized in free-of-acid conditions, using an activated montmorillonitic clay catalyst, known as Maghnite-H+ (Mag-H) as proton source. The electrochemical behaviour of poly(o-anisidine) created using Mag-H (PoANI-MagH) and their copolymers with aniline is quite diVerent of those polymers created in HCl solution. In situ Raman data suggest that the structure of PoANI-MagH is a mixture of conducting (polyaniline-type) and redox (phenoxazine or phenazine-type) segments. Ministerio de Ciencia y Tecnlogía (MAT2004-1479); Generalitat Valenciana (GRUPOS04/75); Programa Juan de la Cierva.

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(111) and Pt(100) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C–N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(111)–CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C–N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media. Ministerio de Ciencia y Tecnología (MAT2004-1479); Generalitat Valenciana (GRUPOS04/75 y GV5/136) Programa Juan de la Cierva.

A large number of porous carbon materials with different properties in terms of porosity, surface chemistry and electrical conductivity, were prepared and systematically studied as electric double layer capacitors in aqueous medium with H2SO4 as electrolyte. The precursors used are an anthracite, general purpose carbon fibres and high performance carbon fibres, which were activated by KOH, NaOH, CO2 and steam at different conditions. Among all of them, an activated anthracite with a BET surface area close to 1500 m2/g, presents the best performance, reaching a value of 320 F/g, using a three-electrode system. The results obtained for all the samples, agree with the well-known relationship between capacitance and porosity, and show that the CO-type oxygen groups have a positive contribution to the capacitance. A very good correlation between the specific capacitance and this type of oxygen groups has been found. The authors thank MEC for financial support (Project PPQ2003-03884).

The electrochemical reactivity of dissolved SO2 on glassy carbon (GC) electrodes was studied in sulfuric and perchloric acid solutions. The surface changes accompanying voltammetric scans were analysed with the aid of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of the GC pretreatment (polished versus electrochemically activated) on the oxidation of SO2 was examined. It was found that GC samples electrochemically treated so to develop a reduced graphite oxide film on the surface were more active for SO2 oxidation. The reduction of SO2 was observed to take place at potentials below 0.0V to yield soluble sulfide species. This species was reoxidized on positive scans to form a sulfur deposit, consisting of an underlying layer of chemisorbed sulfur (161.9–162.3 eV)and an on-top layer of bulk elemental sulfur with S8-like structure (163.6–163.8 eV). Surface sulfur did not impart electrocatalytic activity for the oxidation of SO2. Spanish Ministerio de Ciencia y Tecnología (Projects MAT2001-1007 and MAT2004-01479)

The electrochemical oxidation of 2,3- 2,4- and 2,5-diaminophenol, on platinum electrode, in acid medium was studied using cyclic voltammetry, in situ UV–vis and in situ FTIR spectroscopies. The spectroscopic data indicates that 2,4-diaminophenol suffers hydrolysis giving the formation of 2-amino-hydroquinone/2-amino-p-benzoquinone in solution. The oxidation mechanism of 2,5-diaminophenol is similar to the p-phenylenediamine giving 2-hydroxy-p-benzoquinoneimine and its hydrolysis product, 2-hydroxy-p-benzoquinone. The electrochemical results suggest that 2,3-diaminophenol generates a non-electroactive polymeric material on the electrode surface. Ministerio de Educación y Ciencia (MAT2004-1479); CONICET, FONCYT, Agencia Córdoba Ciencia y SECyT-UNRC.

A novel kind of composites is synthesized due to the outstanding properties of carbon materials. Metallic platinum is deposited on porous carbon discs by means of Potential Step Deposition (PSD) under potentiostatic conditions. Afterwards, the Pt-coated discs were covered completely with colloidal zeolite (silicalite-1) crystals by means of the novel ElectroPhoretic Deposition (EPD) methodology. After standard hydrothermal treatment, the seed crystal coating becomes continuous, crack-free and wellintergrown, giving rise to a layer of silicalite-1 crystals of different sizes. It must be noted that Pt combined with the secondary growth methodology has a extremely important effect on the orientation of the growing zeolite crystals. These novel materials have a wide range of potential applications as membrane reactors and/or catalyst membranes after activation (i.e. template removal by calcination) of the zeolite crystals. Ministerio de Ciencia y Tecnología (PPQ-2003-03884)

The electrocatalytic behaviour of poly(aniline-co-4adpa), Pan-4adpa, films against some redox couples and ascorbic acid was tested in aqueous buffering solutions of pH = 5. The film catalysed the redox process of all the couples investigated although it has been observed that positively charged species such as dopamine/dopaminequinone display more irreversible voltammetric behaviour than negative (ferro/ferricyanide) or neutral (hydroquinone/quinone) ones. The voltammetric results point that the catalytic sites of the Pan-4adpa are probably located at the surface of the film. The oxidation peak of ascorbic acid on Pan-4adpa films is shifted 170mV to more cathodic potentials with respect to the Pt with no generation of adsorbed residues. Ministerio de Ciencia y Tecnlogía (MAT2001-1007)(REN2001-2304-C02-02/TECNO)

Two methods have been used for the deposition of Pt particles on synthetic boron-doped diamond (BDD) surfaces: chemical deposition and electrodeposition under potentiostatic conditions. However, electrodeposition leads much higher platinum dispersion than chemical deposition. The mechanism of nucleation and growing of the electrodeposited platinum was investigated by means of chronoamperometric studies in acid medium. The electrodeposition on diamond surfaces shows a mechanism of progressive nucleation as deduced from the chronoamperometric studies in acid medium. The stability of the deposited platinum is very low and the platinum particle are dissolved/detached by cycling. The modified BDD electrodes by deposition of platinum have been tested for the oxidation of methanol, showing that multi-step deposition results in higher values of surface and mass activities for methanol oxidation than one-step deposition process. Ministerio de Ciencia y Tecnología (MAT2001-1007)

The electrochemical oxidation of aniline and p-aminodiphenylamine (ADPA) was carried out in a phosphate buffer solution at pH 5. Cyclic voltammetry and ‘‘in situ’’ FTIR spectroscopy were combined to study the redox behavior of the oxidation products. When ADPA is oxidized in the presence of aniline, two redox processes are observed. One of these redox processes is related to a soluble species, while the other pertains to a species attached to the electrode surface. Only those films synthesized from ADPA oxidation in the presence of aniline are electroactive in this buffered medium. No evidence pointing to the occurrence of autocatalytic polymerization exists under the experimental conditions employed. Ministerio de Ciencia y Tecnología (MAT2001-1007)(REN2001-2304-C02-02/TECNO); Generalitat Valenciana (GV01-313).

Carbon–ceramic composites have been prepared and characterised by different techniques (electron microscopy, X-ray microanalysis, X-ray diffraction and cyclic voltammetry). The effect on the conductivity of the thermal treatment temperature of the composites and the structure of the starting ceramic has been analysed. The results demonstrate that the layered structure of the clay determines their conductivity. The composites prepared are conductors and the conductivity goes through a maximum with increasing thermal treatment. Platinum has been successfully deposited on the carbon–ceramic composite by chemical and electrochemical methods. A better distribution of platinum and smaller particle sizes are obtained by the electrochemical method. The direct electrooxidation of methanol in acid medium has been studied on platinum-modified carbon–ceramic electrodes. Dirección General de Investigación en Ciencia y Tecnología (AMB1999-1595-CE); Ministerio de Ciencia y Tecnología (MAT2000-0621).