Portugaliae
Electrochimica Acta

The redox reaction of dopamine adsorbed layer on gold is studied. The adsorption takes place at open circuit condition. The adsorbed substance presents a reversible oxidation of the OH groups on the ring, and an irreversible oxidation at higher potentials. The dopamine metal bond is weak and the substance may be removed by a physical procedure. Moreover, multilayers are formed over the first layer. An estimation of the dopamine co-area over gold is reported.

Ti-supported electrodes of nominal composition Ti/Iro.3Ti(o.7-x) Cex02 (0

The formation of conducting polymer films on electrodes by electropolymerisation of activated pyrrolic esters together with their characterisation is presented. Electrochemical evidence for the formation of by-layer polymer films is also reported Modification of the films by reaction on the activated carbonyl esters is described.

This paper reports on the electrochemical characterisation of the oxide film grown on niobium in a borate buffer solution of pH 8.8 at room temperature. The formation of a duplex oxide, probably NbOx(x= 1.2) / Nb205, is suggested by cyclic voltammetry results. Peak currents and scan rates showed a linear dependency when plotted in the log-log plane, exhibiting a unity slope indicating control by a surface process. Electrochemical impedance spectroscopy confirmed the voltammetry results. Impedance spectra were conducted within the potential domains of both anodic peaks after 10 cycles at 200 mVs"1. Bode plot analysis and simulation by the equivalent circuit approach suggested an extra time constant when cycling was extended to include the second peak. The stability of the oxide film was tested in 0.5 M sodium chloride solutions at a low scan rate (0.2 mVs"1) showing no breakdown up to 2500 mV (SCE).

A uniformly rich molybdenum film was deposit on aluminium, without the use of external polarisation, using a buffer and a complexant. Potential - time curves showed that the coating is fully-grown within 60 seconds of immersion. Protective films formed within a narrow range of pH, from 4 to 6. Lower pH values, near those used for Cr treatment, gave rise to hydrous blue Mo(V) compounds with little or no protecting ability whilst higher pH values did not allow the coating to be formed probably due to insufficient thinning of the air formed alumina film. Stability of the produced coatings was assessed by polarising the samples to breakdown in a 0.5 M NaCl solution with added carbonate/bicarbonate. Optimisation of the coating produced a pitting resistance comparable to that of chromate conversion coatings. The mechanism of film formation is briefly discussed.

Tungsten can be successfully implanted on aluminium forming a solid solution. SIMS, XPS and AES analysis showed that almost no tungsten was found in the passive film formed on the alloy in 0.6M NaCl solution. The beneficial effect of tungsten in the increase of the pitting potential of the alloy is due to the ennobling of the pitting process caused by the presence of metallic tungsten. This element modifies the thermodynamics and kinetics of the dissolution and facilitates hydrogen evolution inside the incipient pits, diminishing the ability of the metal to maintain the critical pH associated to stable pitting.

This communication follows a previous work concerning indirect electrochemical reduction of dyes [1] and its application on dyeing control with sulphur dyes. The study concerns the cathodic peak intensity variation with sulphur dye C.I. Leuco Sulphur Black 1 (Black Diresul RDT liq.) concentration, in the presence of a mediator, iron/triethanolamine (FeWTEA), in alkaline media.

The electrochemical reduction of azo dyes in aqueous alkaline solutions is investigated. Cyclic voltammetry, controlled potential electrolyses, chronoamperometry and steady state voltammetry at microelectrodes were used to provide insight into the reduction process. With basis on the data obtained from the experimental techniques mentioned above, a mechanism for the reduction reaction is proposed.

A comparative study of heme proteins horse heart cytochrome c and cytochrome c3 of Desulfovibrio vulgaris (strain Hildenborough) using different electrochemical techniques (linear scan and cyclic voltammetry, differential pulse and square wave voltammetry) with platinum and gold macro and microelectrodes is presented. The electrochemical response was evaluated analysing the reversibility of the electrode process and the formal potentials determined. Diffusion coefficients for both proteins were also calculated from the voltammetric data. The electrochemical behaviour at macro and microelectrodes was analysed and the advantages of microelectrodes pointed out.

The electrochemical behavior of lignin, in alkaline medium, was studied by cyclic voltammetry and compared with that of some lignin model compounds e. g. guaiacol, eugenol, vanillic alcohol and vanillin, in order to elucidate the process involved in electrode reactions. Galvanostatic electrolyses of lignin were carried out using different electrode materials in order to investigate the influence of electrode material on the product distribution.

The influence of experimental parameters on the yields and stereochemistry of Wittig reaction was studied. The synthesis of stilbene initiated by different electrogenerated bases was used as a model reaction. Preparative electrolyses were carried out in different conditions including constant potential or constant current with different electrode materials and using solvents of different polarity. Both the yield and the stereochemistry of the reaction are affected by the electrolysis experimental conditions. Hence, the proper selection of experimental conditions in Wittig reactions allows the choice of the stereosselectivity of the reactions and the optimization of yields.

Sb doped tin dioxide films were prepared by thermal decomposition of SnCI4.5H20 and SbCl3 mixtures applied on pre-treated Ti surfaces. Precursor solutions containing 20 % p/v SnCl4.5H20 and 0.1, 0.2 or 0.3%'p/v SbCl3 were used. The influence of Sb on film morphology and on electrochemical activity were assessed by SEM and cyclic voltammetry in solutions containing ferri-ferrocyanide couple, respectively. In general, the films were quite adherent to the substrate, with mud like cracked appearance when observed by SEM. Their conductivity increased with the SbCl3 content in the mixture. Organic oxidation at the Sn02-Sb205 interface was found to be in the same potential domain to that observed on Pt polycrystalline electrodes suggesting a common mechanism. Electrocatalytic performance was evaluated regarding the electroconversion of 3,4-dimetoxibenzoic and 3,4-dihidroxibenzoic acids, for a specific electrolysis condition.

In this paper, the use of digital simulation as a tool to understand electrochemical data is discussed. The various approaches to digital simulation of electrochemical processes will be reviewed, and some applications of these methods to the interpretation of experimental results are presented.

The Ibero-American Map of Atmospheric Corrosiveness (MICAT) project was set up in 1988 sponsored by the International Ibero-American Programme "Science and Technology for Development (CYTED)". Fourteen countries have been involved in the project: Argentina, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Mexico, Panama, Peru, Portugal, Spain, Uruguay and Venezuela. Research has been conducted both at laboratories and in a network of 72 atmospheric exposure test sites throughout the Ibero-American region, thus considering a broad spectrum of climatological and pollution conditions. This paper presents a summary of some of the results obtained in one-year atmospheric exposure testing of carbon steel, zinc, copper and aluminium: corrosion rate, morphology of attack of the base metal and of the corrosion products formed, their nature and electrochemical properties. The Thematic Network "Anti-Corrosion Protection of Metals in the Atmosphere" (PATINA) was constituted in Lisbon in December 1994, upon the finalization of the MICAT project. The network is participated by the fourteen countries mentioned above plus Bolivia. One of the main tasks of this network is to evaluate the corrosion protection behaviour of a wide range of conventional and advanced coatings in typical atmospheres of the Ibero-American region. This paper presents an overview of the organizational structure of the network and of the coating materials being studied.

The addition of tefra-alkylammonium salts, namely fefra-methylammonium, tefra-ethylammonium, tefra-butylammonium and tefra-hexylammonium salts, to the supporting electrolyte, in the presence of different metal ions, does not change the observed cathodic current for shorter carbon chains. However, an important effect is observed when n > 4 (number of carbon atoms of each chain). This is shown through the polarograms which were recorded for different solutions of cadmium, zinc and manganese ions, in the presence and absence of those ions. The interpretation based on electrocapillary curves has shown that electron transfer through the double-layer becomes more difficult as the length of the carbon chain increases. Polarographic and electrocapillary experiments were followed all over.

A comment from a reader of a paper on the definition of electrolyte and the author's reply is presented.

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.