Search

The electrochromic reaction of a tungsten trioxide electrode prepared by electrochemical deposition was studied. Chronopotentiometric experiments associated with transmittance measurements were carried out for several film thicknesses. The dependence of electrochromic efficiency on the coloration/bleaching current density, the wavelength of the light source and the film thickness were analysed. The mass and structural changes due to the electrochromic reaction were followed using a quartz crystal microbalance and stress experiments respectively. Film formation and dissolution processes for WO 3 in acidic media are also discussed.

In recent years many scientists have devoted a great deal of attention to study of the conductive and superconductive properties of alkali-metal-doped C,, [l-31. On exposure to alkali vapor, the conductivity of A$, (A = K, Rb, Cs) first increases and then decreases depending on the degree of doping x [4,51. These studies were done immediately after the synthesis of C, by KrHtschmer et al. [61. The changes in electronic structure of C, induced by doping with alkaline metals have been investigated by several techniques [7-91 and recently optical absorption spectra of these systems have been reported [lo121. A change in color of C,, thin films from yellowbrown (undoped state) to silver-black when doped with alkali metals had already been observed [5]. Electrochromism can be generally defined as the phenomenon of reversible color change brought about by the passage of an electric current. The current causes a chemical change, an oxidation or reduction reaction, which is accompanied by a change in the optical absorption of the material. Among inorganic electrochromic materials, WO, [13-X] and NiO, [15,17], have been widely studied. There are also some organic materials such as conductive polymers [18,191 which present electrochromism when they are oxidized or reduced. All these materials undergo an electrochemical doping process where the injection or ejection of electrons is compensated for by the insertion or deinsertion of ions to maintain electroneutrality. Recently, Chabre et al. have reported interesting results

The electrochemical intercalation of oxygen in La 2 CuO 4 single crystals was studied using electron paramagnetic resonance and magnetic susceptibility measurements. Chronoamperometric experiments showed that, in the intercalation process, the O 2− diffusion in single crystals is extremely slow ( D ≈ 10 16 cm 2 s −1 ). This diffusion coefficient depends strongly on temperature and the enthalpy diffusion was found to be ca . 750 kJ deg −1 mol −1 . Crystals under electro-oxidation for one to two weeks still show the presence of the antiferromagnetic and a superconducting phases. This was supported by the simultaneous observation of line splitting in the EPR spectra and superconducting diamagnetic signal.

The electrochemical behavior of poly(methylene blue) on different electrodes has been investigated by electrochemical quartz crystal microbalance and in situ spectrophotometric measurements coupled to cyclic voltammetry. Polymeric films were obtained potentiodynamically and the charge transport mechanism was analyzed. The electrochemical results show that polymer electroactivity depends not only on pH but also on the substrate. Charge compensation changes with both pH and the size of the anions showing a transition in the pH range of polymer pKa. It was demonstrated by spectroelectrochemical experiments that the electroactivity of the film depends on the radical/radical cation equilibrium. The potentials where the most electroactive species are formed have been determined. Fil: Pfaffen, Maria Valeria del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Ortiz, Patricia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Córdoba de Torresi, Susana I.. Universidade de Sao Paulo; Brasil Fil: Torresi, Roberto M.. Universidade de Sao Paulo; Brasil

The ionic liquids (ILs) 1-ethoxyethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [EtO(CH(2))(2)MMI][Tf(2)N], and N-(ethoxyethyl)-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide, [EtO(CH(2))(2)MMor][Tf(2)N] were synthesized, and relevant properties, such as thermal stability, density, viscosity, electrochemical behavior, ionic conductivity, and self-diffusion coefficients for both ionic species, were measured and compared with those of their alkyl counterparts, 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [BMMI][Tf(2)N], and N-n-butyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide, [BMP][Tf(2)N] and N-n-butyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [BMMor][Tf(2)N]. This comparison was done to evaluate the effects caused by the presence of the ether bond in either the side chain or in the organic cation ring. The salt, LiTf(2)N, was added to the systems to estimate IL behavior with regard to lithium cation transport. Pure [EtO(CH(2))(2)MMI][Tf(2)N] and their LiTf(2)N solutions showed low viscosity and the highest conductivity among the ILs studied. The H(R) (AC conductivity/NMR calculated conductivity ratio) values showed that, after addition of LiTf(2)N, ILs containing the ether bond seemed to have a greater number of charged species. Structural reasons could explain these high observed H(R) values for [EtO(CH(2))(2)MMor][Tf(2)N].

The electrochemical redox mechanism of a dodecyl sulfate-doped polypyrrole was studied in detail by electrogravimetry using a quartz crystal microbalance. In order to distinguish the nature of the inserted/deinserted species, different salts were used as aqueous electrolytes. A quantitative analysis of the results indicated that the surfactant counter anion was trapped in the polymer matrix and that both anions and cations of the electrolyte play an important role in the redox processes. Quantitative calculations showed that the hydration sphere of these ions must be taken into account when dealing with the redox processes of conductive polymers adhered to the surface of electrodes.

The time-variations of the double-layer capacitance and of the oscillation frequency of an electrochemical quartz crystal microbalance are simultaneously recorded to determine the kinetics of adsorption of bovine serum albumin on a gold electrode. Both variations can be fitted by a sum of exponential functions. It is established that for the steps associated with a mass change both methods provide the same values for the time-constants. This result validates the double-layer capacitance measurement method, which is indirect, as a tool for determining, in situ, rhe kinetics of protein adsorption. Finally, it is established that, in the experimental conditions used here, the oscillation of the quartz crystal modifies, with respect to the nonoscillating quartz, the kinetics of adsorption of the macromolecules

The potentiodynamic oxidation of zirconium, zircaloy-2 (Zry-2) and zircaloy-4 (Zry-4) was studied in the 0 V ⩽ V ⩽ 8 V potential range. Side reactions take place during the oxidation of Zry-2 and Zry-4 in phosphate electrolytes. With Zry-2, oxygen evolution occurs at high anodic potentials. The oxidation of the alloys in nitric acid shows dissolution of their minor alloying elements but no oxygen evolution at high potentials. The role played by the alloying elements in connection with the appearance of side reactions is discussed. The oxide film were characterized by impedance measurements, X-ray photoelectron spectroscopy and Auger spectroscopy.

NiO(OH)x films deposited by e−-beam evaporation have been investigated by means of current voltage graphs (CVG), reflectance voltage graphs (RVG), quartz crystal microbalance (QCM) and fast Fourier-transform infrared spectroscopy (FTIR). Based on these results a new model is developed which supports H+ ejection as well as OH− injection during the coloration process and solves a virtual contradiction of other experimental findings on reactively evaporated NiO(OH)x films.

Highly stable and crystalline V(2)O(5) nanoparticles with an average diameter of 15 nm have been easily prepared by thermal treatment of a bariandite-like vanadium oxide, V(10)O(24) x 9 H(2)O. Their characterization was carried out by powder X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopies, and transmission electron microscopy (TEM). The fibrous and nanostructured film obtained by electrophoretic deposition of the V(2)O(5) nanoparticles showed good electroactivity when submitted to cyclic voltammetry in an ionic liquid-based electrolyte. The use of this film for the preparation of a nanostructured electrode led to an improvement of about 50% in discharge capacity values when compared with similar electrodes obtained by casting of a V(2)O(5) xerogel.

Particulas coloidais tem sido empregadas na sintese dirigida por molde de diversos materiais, tais como semicondutores, metais e ligas. Esse metodo permite um controle da espessura do material resultante atraves da escolha adequada da carga aplicada no sistema e e possivel produzir materiais densamente depositados, sem rachaduras. Esses materiais sao fidedignos a estrutura do molde e, devido as amplas areas superficiais obtidas, sao muito interessantes em aplicacoes eletroquimicas. Neste trabalho, a distribuicao de um molde de poliestireno monodisperso foi realizada sobre substratos de ouro, platina e carbono vitreo com o intuito de exemplificar a eletrodeposicao de um oxido, um polimero condutor e um material hibrido orgânico-inorgânico, com aplicacoes em supercapacitores e sensores. Os desempenhos dos eletrodos nanoestruturados foram comparados com os analogos massivos e os resultados obtidos sao descritos. Colloidal particles have been used to template the electrosynthesis of several materials, such as semiconductors, metals and alloys. The method allows good control over the thickness of the resulting material by choosing the appropriate charge applied to the system, and it is able to produce high density deposited materials without shrinkage. These materials are a true model of the template structure and, due to the high surface areas obtained, are very promising for use in electrochemical applications. In the present work, the assembly of monodisperse polystyrene templates was conduced over gold, platinum and glassy carbon substrates in order to show the electrodeposition of an oxide, a conducting polymer and a hybrid inorganic-organic material with applications in the supercapacitor and sensor fields. The performances of the resulting nanostructured films have been compared with the analogue bulk material and the results achieved are depicted in this paper.

The electrochromic reaction of a tungsten trioxide electrode prepared by electrochemical deposition was studied. Chronopotentiometric experiments associated with transmittance measurements were carried out for several film thicknesses. The dependence of electrochromic efficiency on the coloration/bleaching current density, the wavelength of the light source and the film thickness were analysed. The mass and structural changes due to the electrochromic reaction were followed using a quartz crystal microbalance and stress experiments respectively. Film formation and dissolution processes for WO 3 in acidic media are also discussed.

The quartz crystal microbalance seems to be a very usefui tool in electrochemical studies, but, up to now, no attempts have been made to calibrate the microbalance under electrochemical conditions. The aim of this paper is to determine not only the average sensitivity for different active areas but also the differential sensitivity as a function of the radial position of a localized change of mass. In this way, for homogeneous mass perturbation, it is possible to calculate the change of mass (Am) from the frequency shift (AJ) for different active areas by taking into account the average sensitivity value. In the case of localized Am, the differential sensitivity value allows one to calculate hm from hfif the position of the event is known. The calibration procedure was made for an AT-6 MHz quartz crystal. Quartz crystals are important sensing devices in liquid phase. They can be used to monitor changes in electrode mass (1-3) or changes in the liquid properties (4, 5). In an electrochemical process, a shift of the value of the quartz crystal resonance frequency (fo) can be attributed to a change in mass (Am) of the electrode, provided that the true relationship between hf and Am is known. The problem of the sensitivity of the quartz crystal microbalance (QCM) has been already dealt with in the air (6-8). The differential sensitivity of the QCM has been calculated from the local damage produced in a thin polymer film by an ion beam sputtering. In the liquid phase the distribution of the vibration amplitude of the quartz crystal has been investigated by putting a tungsten wire probe in contact with the quartz crystal to provoke a change in frequency (9, 10). The results obtained in both liquid and gas phases are rather similar, in spite of the properties of liquid phase which extend the vibration of the quartz crystal even beyond the active region defined by the metal deposit. These works show the complexity of the system and that the boundary conditions used for the derivation of Sauerbrey's equation (11, 12) are not always fulfilled. The problem of the QCM calibration has been extensively studied in air. on the contrary, despite the wide use of the QCM in electrochemistry, the calibration procedure of this technique in electrochemical conditions is not depicted in the literature. The aim of this work is to calibrate the electrochemical quartz crystal microbalance (EQCM), not only in the case where hm is uniformly spread on the active electrode surface, but also for localized mass changes. The last case is very relevant to all electrochemical phenomena which produce a change of mass on a small area, e.g., in localized corrosion or gaseous bubble evolution. The general case where the mass change is continuously but nonuniformly distributed across the surface is not addressed in the paper.

In the present paper the quartz crystal microbalance is used as a sensitive detector of mass changes taking place during an electrochromic process. Electrochemical and electrochromic characteristics of nickel oxide electrodes strongly depend on the preparation method of the samples. Three different types of materials are studied and their electrogravimetric responses compared: hydroxide film prepared by cathodic deposition from a Ni2+‐containing solution; porous and stoichiometric nickel oxide films formed by anodic oxdation of a nickel electrode in a concentrated solution; and nonstoichiometric films prepared by electron‐beam evaporation. A formula describing the colored film is proposed, taking into account the effect of hydrated alkaline cation (Li+; K+) incorporation.

Numerous electrochemical processes of practical interest involve gas production at an electrode surface. The subsequent bubble evolution leads to a random behaviour of the observed potential when the electrode is current controlled. It has been shown that these potential fluctuations are, at least partially, related to a screening effect of the surface by the gas bubbles [l] which gives rise to an additional electrolyte resistance and hence to ohmic drop fluctuations. At low current densities it was shown that the ohmic drop and the overvoltage increase linearly when the bubbles grow and decrease suddenly when a bubble detaches from the surface [2]. The sizes and times of occurrence of the potential jumps are random and the observed potential is a random signal which was analyzed by spectral analysis [3]. For high values of the electrolysis current the measurement of the power spectral density (p.s.d.) of the potential fluctuations leads to information on the dynamics of the bubble evolution regime, i.e. the mean number of bubbles evolved per time unit, the average bubble detachment radius and the gas evolution efficiency [3]. For low values of the electrolysis current an estimate of the detachment size of the bubbles can be obtained only from the measurement of the power spectral density of the electrolyte resistance fluctuations [4]. However, information concern- ing the physico-chemical details of the bubble detachment is still lacking. Recently, it has been proposed that an electrochemical quartz crystal microbal- ante be used in order to detect electrolytically generated bubbles [5]. The response of the quartz resonance frequency to polarisation current steps has been observed. But probably due to the narrow bandwidth and the low amplification of the electronic equipment the individual transients related to the bubble growth and

The present paper deals with the immobilization of redox mediators and proteins onto protected porous silicon surfaces to obtain their direct electrochemical reactions and to retain their bioactivities. This paper shows that MP-11 and viologens are able to establish chemical bonds with 3-aminopropyltriethoxylsilane-modified porous silicon surface. The functionalization of the surfaces have been fully characterized by energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) to examine the immobilization of these mediators onto the solid surface. Amperometric and open circuit potential measurements have shown the direct electron transfer between glucose oxidase and the electrode in the presence of the viologen mediator covalently linked to the 3-aminopropyltriethoxylsilane (APTES)-modified porous silicon surfaces.

This paper presents the characterization of poly(aniline) (PANI) and poly(methyl methacrylate) (PMMA) coatings obtained by mixing PANI with PMMA aqueous dispersions (latex particles). These dispersions were characterized by using dynamic light scattering for sizing, zeta-potential analysis and thermal analysis. PMMA and PANI/PMMA dispersions show negative charged particles with zeta potential greater than |40| mV, a zeta-average diameter of 64 nm for pure PMMA and a bi-modal particle-size distribution centered at 45 and 120 nm for a mixture with 25% w/w of PANI. Films obtained by casting were characterized by using scanning electron microscopy and they show a conductivity increase upon PANI content reaching a value of 1 mS cm-1 for a film with 25% w/w of PANI. In addition, Raman spectroscopy have shown the presence of the conducting form of PANI in the films and cyclic voltammetry experiments corroborated that they are electroactive in both acid and neutral solutions.

In this work, we present the synthesis and characterization of a hybrid nanocomposite constituted by iron oxide nanoparticles and vanadium oxide/Hexadecylamine (VOx/Hexa) nanotubes. Transmission Electron Microscopy (TEM) images show small particles (around 20 nm) in contact with the external wall of the multiwall tubes, which consist of alternate layers of VOx and Hexa. By Energy Dispersive Spectroscopy (EDS), we detected iron ions within the tube walls and we have also established that the nanoparticles are composed of segregated iron oxide. The samples were studied by Electron Paramagnetic Resonances (EPR) and dc-magnetization as a function of the magnetic field. The analysis of the magnetization and EPR data confirms that a fraction of the V atoms are in the V4+ electronic state and that the nanoparticles exhibit a superparamagnetic behavior. The percentage of V and Fe present in the nanocomposite was determined using Instrumental Neutron Activation Analysis (INAA). Fil: Saleta, Martin Eduardo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Ribeiro Guevara, S.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Sanchez, Rodolfo Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Malta, M.. Universidade Do Estado Da Bahia; Brasil Fil: Torresi, R.M.. Universidade de Sao Paulo; Brasil

The electrochemical polymerization of aniline in a hydrophobic room-temperature ionic liquid and the spectroelectrochemical characterization of the formed film are presented. The polymerization occurs without the presence of acid in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMITFSI), leading to a very stable electroactive material where no degradation was observed even at high applied potentials. Both in situ UV-Vis and Raman spectroscopic studies provided evidence for the stabilization of pernigraniline salt at high oxidation potentials and that this polyaniline state is the conducting form, as was corroborated by in situ resistance measurements. These data are indicative that low conductivity is not an intrinsic property of pernigraniline salt and this point must be reconsidered.

Lithium salt solutions of Li(CF3SO2)2N, LiTFSI, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N(-), bis(trifluoromethanesulfonyl)imide anion, [BMMI][TFSI], were prepared in different concentrations. Thermal properties, density, viscosity, ionic conductivity, and self-diffusion coefficients were determined at different temperatures for pure [BMMI][TFSI] and the lithium solutions. Raman spectroscopy measurements and computer simulations were also carried out in order to understand the microscopic origin of the observed changes in transport coefficients. Slopes of Walden plots for conductivity and fluidity, and the ratio between the actual conductivity and the Nernst-Einstein estimate for conductivity, decrease with increasing LiTFSI content. All of these studies indicated the formation of aggregates of different chemical nature, as it is corroborated by the Raman spectra. In addition, molecular dynamics (MD) simulations showed that the coordination of Li+ by oxygen atoms of TFSI anions changes with Li+ concentration producing a remarkable change of the RTIL structure with a concomitant reduction of diffusion coefficients of all species in the solutions.

The electroformation of silicon oxide was performed in two room temperature ionic liquids (RTIL), l-butyl-3-methyl-imidazolium bis(trifluoromethane sulfonyl) imide (BMITFSI) and N-n-butyl-N-methylpiperidinium bis(trifluoromethane sulfonyl) imide (BMPTFSI). This phenomenon was studied by electrochemical techniques and it was observed that the oxide growth follows a high-field mechanism. X-ray Photoelectron Spectroscopy experiments have shown that a non-stoichiometric oxide film was formed, related to the low water content present in both RTILs (

Le phenomene d'echange d'ions a l'interface de l'electrode (polyaniline) et de l'electrolyte est examine par des mesures d'impedance electrochimique et d'electrogravimetrie

Potentiodynamically grown thin oxide films of zirconium were investigated as a function of the electrode potential, the potential sweep rate and the pH in phosphate electrolytes. The oxides were characterized by coulometric and impedance measurements in the frequency range . The rate of oxide growth changes with the sweep rate according to the high field law. The oxide growth kinetics depends on the pH of the forming electrolyte. The results are interpreted in terms of anion incorporation into the film. The system impedance is characterized by a low‐frequency capacitive behavior associated with the oxide film and by a high‐frequency resistive behavior corresponding to the electrolyte. The oxide capacity was found to be frequency dependent. The oxide impedance can be interpreted in terms of a dielectric relaxation model. A complex dielectric constant was calculated at pH 14.

Repassivation kinetics of metals has been frequently related to the susceptibility to localized types of corrosion such as pitting, crevice corrosion and stress corrosion cracking (SCC). The present paper reviews recent work in our laboratory showing that repassivation kinetic measurements can be successfully used to detect passivity breakdown in metals; a step which followed by localized acidification leads to pitting and crevice corrosion. Similar experiments have confirmed that for SCC a slow repassivation rate is a necessary, but not a sufficient, condition for stress corrosion cracking.

The contact between minor amounts of SO2 and crystalline 1-butyl-3-methyl-imidazolium bromide (BMIBr) causes the almost immediate melting of the ionic liquid (mp 45 degrees C) as well as a dramatic decrease in its viscosity in comparison to the pure molten phase. The same behavior was observed for other halide ionic liquids of higher melting points (70, 135, and 220 degrees C). The Raman spectrum of BMIBr-SO2 clearly indicates a specific charge transfer interaction involving SO2 and the halide. The measurements of ionic conductivity and diffusion coefficients obtained for the neat BMIBr (molten phase) and for the BMIBr-SO2 strongly suggest a higher degree of ionic association in the presence of SO2. Molecular dynamic simulations indicate that although the cation-anion distance is preserved in the short range, there is a variation in the interionic distances in the second shell, leading to a less organized structure in the long range. The modulation of the structural and physical properties of ionic liquids by SO2 and the convenient choice of the ions for gas absorption are suggested.

International audience; Vanadium oxide/polyaniline nanotubes were produced by cationic exchange between hexadecylamine and polyaniline after the synthesis of vanadium oxide nanotubes by sol–gel method followed by hydrothermal treatment. The local structure of this hybrid material was studied by high-resolution transmission electron microscopy, infrared and Raman spectroscopy and small angle X-ray diffraction technique. The results show that polyaniline is intercalated in the interlamellar space of the vanadium oxide nanotube forming a hybrid material with defined morphology. Electrochemical impedance spectroscopy experiments have shown that the apparent diffusion coefficient for nanotubes with template was approximately 1×10−9 cm2 s−1. Nanotubes with polyaniline presented an apparent diffusion coefficient at least one order in magnitude higher than the parent material “with template”, comparable with other vanadium oxide described in the literature, revealing a promising material for utilization as cathode for ion-Li batteries.

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.

Films of non-stoichiometric tungsten oxides have been deposited onto glassy carbon surfaces by electrodeposition from acidic W(VI) solutions and the chemical stability of these oxides was investigated by using the electrochemical quartz crystal microbalance. At these modified surfaces, rotating disc electrode voltammetric experiments indicated that iodate is electrocatalytically reduced in a mass-transport controlled process. The influence of the film thickness on the response to iodate was investigated and the results indicated a linear relationship between catalytic current and film thickness for relatively thin oxide layers. The modified electrode was employed successfully as an amperometric sensor for iodate in a flow injection apparatus. The linear response of the developed method is extended from 5 μmol L −1 to 5 mmol L −1 iodate with a limit of detection (signal-to-noise = 3) of 1.2 μmol L −1 . The repeatability of the method for 41 injections of a 1 mmol L −1 iodate solution was 0.8% and the throughput was determined as 123 h −1 . Interference from other oxidant anions such as nitrate and nitrite was not noticeable, whereas bromate and chlorate interfere at slight levels. The method was used in the determination of the iodate content in table salt samples.

Synthesis and characterisation of new nanocomposites of poly(3-decylpyrrole) (P3DP) and poly(hexadecylpyrrole) (P3HDP) with V 2 O 5 are described. These nanocomposites were characterised using X-ray diffraction (XRD), electrochemical quartz crystal microbalance, electroacoustic impedance (EAI) and cyclic voltammetry. The results were compared with an other nanocomposite, polypyrrole (Ppy)/V 2 O 5 , aiming to verify the influence of the side chains of P3DP and P3HDP on the electrochemical behaviour of V 2 O 5 . These hybrid materials have different structures that modify the electrochemical properties. The side chains of P3DP and P3HDP contributed to greater electrochemical stability than that of Ppy into the V 2 O 5 matrix. This results in a higher specific capacity for the P3DP/V 2 O 5 and P3HDP/V 2 O 5 nanocomposites (115 and 106 Ah kg −1 , respectively) than that of Ppy/V 2 O 5 (50 Ah kg −1 ) after 50 electrochemical cycles.

In recent years many scientists have devoted a great deal of attention to study of the conductive and superconductive properties of alkali-metal-doped C,, [l-31. On exposure to alkali vapor, the conductivity of A$, (A = K, Rb, Cs) first increases and then decreases depending on the degree of doping x [4,51. These studies were done immediately after the synthesis of C, by KrHtschmer et al. [61. The changes in electronic structure of C, induced by doping with alkaline metals have been investigated by several techniques [7-91 and recently optical absorption spectra of these systems have been reported [lo121. A change in color of C,, thin films from yellowbrown (undoped state) to silver-black when doped with alkali metals had already been observed [5]. Electrochromism can be generally defined as the phenomenon of reversible color change brought about by the passage of an electric current. The current causes a chemical change, an oxidation or reduction reaction, which is accompanied by a change in the optical absorption of the material. Among inorganic electrochromic materials, WO, [13-X] and NiO, [15,17], have been widely studied. There are also some organic materials such as conductive polymers [18,191 which present electrochromism when they are oxidized or reduced. All these materials undergo an electrochemical doping process where the injection or ejection of electrons is compensated for by the insertion or deinsertion of ions to maintain electroneutrality. Recently, Chabre et al. have reported interesting results

The concepts of dissipation and feedback are contained in the behavior of many natural dynamical systems. They have been used to predict the evolution of populations leading to the formulation of the quadratic logistic equation (QLE). More recently, the QLE has been used to provide a better understanding of physicochemical systems with promising results. Many physical, chemical and biological dynamic phenomena can be understood on the basis of the QLE and this work describes the main aspects of this equation and some recent applications, with emphasis on electrochemical systems. Also, it is illustrated the concept of potential energy as a convenient way of describing the stability of the fixed points of the QLE.

One of the most important problems associated with use of polyaniline as a cathode material in rechargeable lithium batteries is related to energy density degradation due to the predomination of anion participation in the charge compensation process. This work describes the synthesis of a self-doped polyaniline, poly-(aniline-co-N-propanesulfonic acid-aniline), and evaluates its properties in aqueous acid solutions, with special attention to the increase of proton participation in the electroneutralization mechanism. The characterization was carried out using elemental analysis, FTIR and UV-vis spectroscopies. Electrochemical properties were investigated with the electrochemical quartz crystal microbalance and cyclic voltammetry. The results obtained show that proton participation was increased for the redox process of poly-(aniline-co- N-propanesulfonic-acid-aniline) in relation to polyaniline. Um dos problemas mais importantes associado à utilização da polianilina como material catódico em baterias recarregáveis de lítio está relacionado à degradação na densidade de energia devido à participação massiva de ânions durante o processo de compensação de cargas. Este trabalho descreve a síntese de uma polianilina auto-dopada, poli-(anilina-co-N-ácido propanossulfônico-anilina), e avalia suas propriedades em meio aquoso, considerando o aumento na participação de prótons no mecanismo de eletroneutralização. A caracterização foi feita utilizando análise elementar e espectroscopias no infravermelho e ultravioleta-visível. As propriedades eletroquímicas foram investigadas com a microbalança eletroquímica a cristal de quartzo e voltametria cíclica. Os resultados obtidos mostram que a participação de prótons no processo redox da poli-(anilina-co-N-ácido propanossulfônico-anilina) aumentou, em relação à polianilina.

Supramolecular structures of polyaniline (PANI) and vanadium oxide (V 2 O 5 ) have been assembled via the electrostatic layer-by-layer (LBL) technique. The films were characterized by vibrational analyses which indicated that the interactions between the two components lead to different properties in the films when compared to sol-gel films of the neat compounds. In particular, using surface enhanced Raman scattering we were able to probe LBL film properties that depend on which material comprises the topmost layer.

Vanadium oxide nanotubes constitute promising materials for applications in nanoelectronics as cathode materials, in sensor technology and in catalysis. In this work we present a study on hybrid vanadium oxide/hexadecylamine multiwall nanotubes doped with Co ions using state of the art x-ray diffraction and absorption techniques, to address the issue of the dopant location within the nanotubes' structure. The x-ray absorption near-edge structure analysis shows that the Co ions in the nanotubes are in the 2 + oxidation state, while extended x-ray absorption fine structure spectroscopy reveals the local environment of the Co(2+) ions. Results indicate that Co atoms are exchanged at the interface between the vanadium oxide's layers and the hexadecylamines, reducing the amount of amine chains and therefore the interlayer distance, but preserving the tubular shape. The findings in this work are important for describing Co(2+) interaction with vanadium oxide nanotubes at the molecular level and will help to improve the understanding of their physicochemical behavior, which is desired in view of their promising applications.

Vanadium oxide nanotubes (NTs) were synthesized by the sol-gel method followed by a long-term hydrothermal treatment. The obtained nanotubes have a multiwall structure, and 70% of vanadium ions are in the V4+ state. This percentage was derived by evaluating three components of the magnetic susceptibility; namely, (i) the paramagnetic Curie-Weiss behavior, (ii) antiferromagnetic dimers, and (iii) magnetic trimers. The as-made NTs were annealed in situ in the cavity of the electron paramagnetic resonance (EPR) spectrometer. The line shape changes irreversibly at 390 K, and the EPR susceptibility presents an anomaly at 425 K. These changes are interpreted as a partial oxidation of the V4+ ions and consequently a decrease in the concentration of the magnetic species. The quantification of the V4+ ions of the annealed NTs reveals a diminution to 39% of V4+, a weakening of the Curie-Weiss and antiferromagnetic dimers contributions, and the suppression of magnetic trimers. Vibrational studies confirm the decreas...

not Available.

not Available.

The electrochromic properties of transition metal oxides are a consequence of an ion/electron intercalation process. In nickel oxide electrodes, the electrochemical/electrochromic reaction has been pointed out to be a proton/electron intercalation process. However, recent works showed that the mechanism of the reaction could be much more complex. In this work, we studied the electrochemical reactions of rf sputtered thin nickel oxide films in aqueous electrolytes containing different cations. An electrochemical quartz crystal microbalance has been used in order to follow the mass changes during the experiments. Also, the mechanical stress changes have been measured in situ by an optical technique. The results show that the incorporation of the cations in the film has to be considered; possible reaction mechanisms are discussed in this work.

The electrochromic reaction of cobalt oxide thin films prepared by electrochemical deposition was studied. Chronopotentiometric and potentiodynamic experiments associated with transmittance measurements were carried out. The mass and structure changes due to the electrochromic reaction were followed using a quartz crystal microbalance and stress experiments, respectively. The stoichiometry of the anodically deposited virgin film is discussed.

A corrosion protection coating for AA2024-T3 composed of a blend of camphorsulfonate-doped poly(aniline) (PANI) and poly(methylmethacrylate) (PMMA) is described. The open-circuit potential (OCP) for the bare and coated alloy in H 2 SO 4 solutions is presented vs. time. Raman spectroscopy revealed the oxidation state of the PANI component of the blend, both on undamaged films and as a function of distance away from a scratch on purposefully damaged films. The open-circuit and Raman data show galvanic coupling between the coating and the alloy, causing reduction of the PANI component. Scanning electrochemical microscopy was used to monitor H 2 evolution over a scratch on the surface of either PANI blend or PMMA films coated on AA2024. These experiments show that the scratched surface is highly active toward H 2 evolution when coated with only a PMMA film. In contrast, the blend coating drastically suppresses the amount of H 2 evolution in a scratch. This suppression of H 2 evolution was mimicked by poising the OCP of the PMMA-coated alloy at the same value at which it is poised by the PANI-containing film. It is shown that camphorsulfonate anion has no inhibitory effect on H 2 evolution in scratches on PMMA-coated AA2024.

The local lithium environment in electrochemically lithiated V 2 O 5 xerogel, polyaniline/V 2 O 5 , and sulfonated polyaniline/V 2 O 5 nanocomposites is probed with solid-state 7 Li static and magic angle spinning (MAS) nuclear magnetic resonance (NMR). The line width from the static NMR spectra reveals differences between the lithium environments in the three materials. The MAS NMR spectrum of the V 2 O 5 parent material in its unreduced (as-prepared) state shows the presence of an intrinsic ion-exchange site that can be populated with Li + by simple exposure to LiClO 4 in propylene carbonate (PC). Following electrochemical lithiation, both ion-exchange and intercalated lithium sites are observed. After lithiation, Li + ions at the ion-exchange site can be displaced by exposure to NaClO 4 in PC via a simple ion-exchange process. Both the ion-exchange and intercalated sites are observed for a sulfonated polyaniline/V 2 O 5 nanocomposite while the polyaniline/V 2 O 5 nanocomposite response is dominated by the intercalated lithium site. The results show that charge compensation of the intrinsic negatively charged ion-exchange sites in the V 2 O 5 xerogel by conducting polymers used to form the nanocomposites is important in determining the number and type of Li + sites available.

X-ray absorption near edge spectroscopy ~XANES!, Brunauer-Emmett-Teller surface area, Fourier transform infrared ~FTIR! ,a nd thermogravimetric analysis were used to characterize two xerogels of V2O5 prepared using the vanadate hydrolysis ~i.e. ,t he v-V2O5 material! or the vanadyl tris~isopropoxide! hydrolysis ~i.e., the a-V2O5 material! synthetic routes. XANES spectra were obtained and analyzed for samples at varying degrees of lithiation that were either bathed in 0.5 M LiClO4/propylene carbonate ~PC! supporting electrolyte ~i.e., in situ! or from which the solvent had been removed by treatment under high vacuum ~i.e., ex situ!, as judged by FTIR analysis. The pre-edge, main edge, and edge resonance peak intensities were examined to track the symmetry around the vanadium center. The results for the in situ samples made by both synthetic routes showed that the local symmetry around vanadium did not change significantly forx values ranging from 0 to 0.98, where x represents the degree of reduction in the formulation LixV2O5 . For the ex situ samples, substantial distortion was observed on going from either the hydrated or PC-swollen states to states in which solvent was absent. Further, the XANES spectrum for an unlithiated ex situ a-V2O5 material showed very substantial distortion around vanadium compared to the v-V2O5 material, presumably due to the rapidity of polymerization in the alkoxide synthetic procedure. The galvanostatic intermittent titration technique was used to obtain the apparent Li 1 diffusion coefficient in both materials, revealing Li

The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is extremely consistent, and it becomes a transparent gel from 350 to 850 nm ~visible region!. Moreover, voltammetry and chronoamperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a large variation of transmittance values ~around 60%! when Cu

Composites of V 2 O 5 xerogel with polyaniline (PANI) are prepared from a vanadyl tris(isopropoxide) precursor and aniline monomer by in situ oxidative polymerization of aniline in the sol solution, followed by gelation with the inorganic oxide. The composite is characterized using Fourier transform infrared spectroscopy, X-ray diffraction, electroacoustic impedance, electrochemical quartz crystal microbalance (EQCM), electrochemical impedance, in situ resistance, cyclic voltammetry, UV-visible (UV-vis) spectroscopy, and multiple charge/discharge measurements. Electrochemical impedance data at -0.7 V give a value for the Li diffusion coefficient in the composite of 2 × 10 11 cm 2 s 1 , in contrast to the value of 3 x 10 -12 cm 2 s -1 obtained for V 2 O 5 . EQCM data show that charge compensation in the composite is achieved predominantly by Li + electromigration, as is also the case for V 2 O 5 . In situ resistance measurements reveal that the composite has a very high conductivity over the potential range 0.4 to -0.5 V. In contrast, V 2 O 5 exhibits much lower conductivity over this range and also shows a deep minimum in conductivity near -0.2 V. Both materials become more resistive at potentials more negative than -0.5 V. UV-vis spectroscopy of the materials reveals changes in the optical bandgap that are consistent with these resistance changes Finally, the composite shows excellent stability toward repeated charge/discharge cycling.

Electrochromic nickel oxide films are studied by means of cyclic voltammetry and photometric measurement. A moving intercalation front model is shown to be consistent with the features of the reflectance curves.