Portugaliae
Electrochimica Acta

To evaluate the response of pyrite and arsenopyrite to oxidizing conditions, an electrochemical approach was employed, to set boundaries for the influence of the arsenopyrite content. The effects of galvanic interactions and local pH on the oxidation reaction of pyrite were also studied. With this purpose, artificial two-mineral electrodes were constructed ranging in concentration from 20-80 % arsenopyrite. The resulting cyclic voltammograms were analyzed and relative quantities of oxidation products were evaluated.

The aim of this paper is to evaluate the use of molibdate solutions for pre-treatments of zirconiun surfaces. Zirconium electrodes were held immersed in molibdate solutions for predetermined time intervals. With the subsequent determination of the pitting nucleation potential and the analysis of the surface morphology, it was possible to evaluate the effect of the molibdate concentration and of the solution pH on the pitting corrosion processes. Among the most important results, two are worthy of attention: (i) for all pH values, the immersion of zirconium electrodes in molibdate solutions hinders the pitting corrosion process of the metal, shifting the pitting nucleation potential to more positive values, (ii) the more pronounced shifts of the pitting nucleation potential were observed in alkaline solutions with high molibdate concentration and in acid solutions with low molibdate concentration; this effect was attributed to the adsorption of different species formed at different pH values.

The influence of potential-scan number on the Schiff base self-assembled monolayer was probed by the Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) techniques for the first time. The results showed that the charge transferring resistance (Rct) could be reduced with the potential-scan, suggesting that the structure of the self-assembled monolayer was altered. Also, the relationship between the content of C=N group, represented approximately by the reduction electric charge (Qr), and the monolayer’s packing degree which was represented by the value of Rct, was described. Providing a new way to change the interface characterization is the main contribution of this paper.

Hybrid films of poly(o-aminophenol) and nickel sulfonated phtalocyanine are produced by electrochemical polymerization of o-aminophenol in the presence of the metal complex. The irreversible incorporation of the metal complex into the hybrid films is tested using reflectance infrared spectroscopy. Electrodes modified with poly(o-aminophenol) alone and the hybrid film show a higher electrocatalytic activity, for NO oxidation, than the base substrate electrode (glassy carbon). The hybrid films show higher currents and lower oxidation overpotential. The oxidation peak current is linear with concentration up to 200 sm M of NO.

Copolymers of aniline and 2-aminobenzoic acid are prepared by chemical copolymerization. The copolymers are soluble in basic media and thin films are prepared, onto glassy carbon electrodes, by evaporation of the solutions. The modified electrodes show a voltammetric response, with two peaks, similar to polyaniline with two peaks. The dependence of both peak potentials on pH is similar to that of PANI, suggesting that proton expulsion is the mechanism of charge compensation on oxidation. The mechanism is confirmed by Probe Beam Deflection, which shows proton expulsion on oxidation. However, while polyaniline films exchange mainly anions at pH>0, poly(aniline-co-(2-aminobenzoic acid)) (p2ABA) film exchange protons up to pH 4 .

The complete theory corresponding to a CE mechanism when applying cyclic chronopotentiometry to a spherical electrode of any size is developed. The influence of several variables on the transition time ratios, such as the electrode radius, rate constants of the homogeneous chemical reaction and current density, is discussed. A simple and practical criterion based on the variation of current density applied to the electrode is proposed for the detection of a CE mechanism.

Polyelectrolyte thin films constructed using the method proposed by Decher and co-workers are studied using several electrochemical techniques, such as cyclic voltammetry and linear sweep voltammetry with rotative disc electrode. The main goal of this work is to evaluate the influence of the number of layers and the charge of the external layer in thin film permeability. These films seem to have electrochemical properties strongly influenced by deposition conditions. It’s shown that the increased number of layers lowers film permeability.