E. Fatas

Electroactive polymer films for stainless steel corrosion protection

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.

Determination of the flat band potential for In2S3/electrolyte interfaces

Abstract Flat band potentials ( V fb ) of In 2 S 3 polycrystalline thin films obtained by chalcogenization of electroplated metallic indium films on Ti substrates with a flowing stream of H 2 S gas have been obtained. The variation of this potential with different redox couples, solution concentration and pH values has been studied. Photoelectrochemical characterization of the electrodes was accomplished in aqueous polysulphide solutions and the application of the Gartner—Butler model to the semiconductor/electrolyte interface makes it possible to obtain the semiconductor energy gap. The value obtained is 2.06 eV, corresponding to a direct allowed transition.

Voltammetric study of the electrodeposition of CdS films from propylene carbonate solutions

Abstract The mechanism of electrodeposition of CdS on Pt and Au electrodes has been studied in proplyene carbonate solutions by performing cyclic voltammetry at stationary electrodes in solutions containing both Cd(II) ions and elemental sulphur. The formation of an initial layer of CdS by underpotential deposits of Cd reacting with chemisorbed sulphur is suggested. The growth of the films takes place afterward by reduction of sulphur to sulphide, which forms the deposit with Cd(II) from the solution.

Electrochemical study of hydrogen absorption in polycrystalline palladium

Abstract The hydrogen reactions on polycrystalline Pd in 0.1 M NaOH at 25°C have been studied by using transients at constant potential, and by impedance spectroscopy and X-ray diffraction techniques. At potentials, Es, more positive than the reversible potential, Er, for the H2 evolution reaction, the current-time response and the impedance data indicate H atom diffusion into the bulk Pd. The X-ray diffraction pattern of electrodes cathodized during 20 min at these potentials are similar to those obtained for Pd. At Es

On the influence of adsorption of electroactive species on the polarographic determination of stability constants

Abstract The influence of specific adsorption of electroactive species on the polarographic determination of stability constants is studied quantitatively. An expression for the term that permits correction of the effect of the adsorption and the “true” value of the constants to be obtained from the “apparent” value is deduced. The sense of the correction shows that the “apparent” constants are always higher than the “true” ones, which is in agreement with some experimental observations. Analysis of the dependence of the correction term on the adsorption parameters shows that even moderate adsorption exerts a significant influence on the values of the stability constants.

Study of the anion-induced adsorption of In(III) from iodide solutions at the dme by ac measurements

Abstract The reduction of In(III) in solutions containing 0.5, 0.75 and 1 M of NaI and with an ionic strength of 1.00 maintained with sodium perchlorate, has been studied by measuring the interfacial admittance spectra at different dc potentials of the dropping mercury electrode ( dme ). The frequency dependence of the admittance corresponds to that of a reversible electrode reaction with reactant adsorption. The adsorption parameters have been determined and the strange behaviour of u′ , which increases with cathodic potential must be pointed out. This seems to indicate that the adsorption occurs beyond the potential at which begin the reduction of indium. It is shown that the potential dependence of the adsorption parameters can be mathematically described by a Langmuir isotherm with the adsorption free energy being at least a quadratic function of potential. Strong adsorption effects have not been found.

Degradation of DMFC using a New Long-Term Stability Cycle

The understanding of the degradation mechanisms involved in the performance of direct methanol fuel cells (DMFCs), constitute important matter for the future implementation of this technology. In this context, it is necessary to develop new and reliable analysis tools to simulate realistic operating conditions. To reflect these, the present study used a “start-run-stop-run’” (SRSR’) test in three different characteristic voltages (at open-circuit potential (OCP), 0.3, and 0.1 V). The electrical loss performance at different operating times (0, 22, 40, and 60 h) working under SRSR’ test was followed by analysis of polarization curves and electrochemical impedance spectroscopy (EIS). The results reveal a decrease of 65% in the maximum density power, 30 mW/cm2, with a degradation rate of 1.2 mV/h at 50 mA/cm2. In addition, the contribution to the overall loss of fuel-cell performance was observed to follow the order: anode reaction > cathode reaction > IR resistance. Ex situ characterizations confirm this reduced activity due to catalyst agglomeration and the dissolution of the anode cocatalyst (Ru). Finally, X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed 20.8% and 24.2% losses of specific surface area for the anode and cathode, respectively. The performance losses of the fuel cell by the new SRSR’ cycle and constant voltage (CV) were compared. The results show that the CV test is significantly more aggressive than the SRSR’, following the order cathode reaction > anode reaction > IR resistance to the overall performance losses.

New supramolecular interactions for electrochemical sensors development: different cucurbit[8]uril sensing platform designs

Three different strategies for cucurbit[8]uril immobilization on a glassy carbon electrode have been assayed. The electrochemical properties of the resulting modified electrodes in solutions containing neutral, positively and negatively charged potential cucurbit[8]uril guests were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The comparison of the electrochemical behaviour exhibited by the unmodified electrodes against various probes, with respect to that of each modified electrode, resulted in an appropriate method to choose among different strategies for the development of electrochemical sensors. These sensors are based on the incorporation of the cucurbit[8]uril molecular selection properties that depend on the chemical characteristics of the potential analytes. Furthermore, atomic force microscopy was employed for the characterization of the different surfaces developed.

Application of digital simulation to the study of non-linearity in electrode processes

Abstract The digital simulation method has been used to analyse the linearity of a simple electrode process. To accomplish this, some of the parameters which characterize these types of process were modified in different cases. The results obtained have been represented graphically and show clearly the perturbations which the introduced in the linearity of the system.

On the nature of the adsorbed species and mechanism of adsorption of In(III) from iodide solutions at the dme

Abstract The reduction of In(III) in solutions containing 0.05, 0.1 and 0.25 M of NaI and with an ionic strength of 1.00 maintained with sodium perchlorate, has been studied by means of interfacial admittance measurements at different frequencies and dc potentials of the dropping mercury electrode. Our results demonstrate that the process takes place with specific adsorption of electroactive species. The adsorption parameters and their dependence with potential have been determined. From the analysis of our results, together with those obtained in a previous study at higher concentrations of I − , it can be deduced than InI + 2 is the species preferentially adsorbed, this adsorption taking place via a bridge-like mechanism, through I − ions previously adsorbed.