Search

Experimental results are presented on the electrochemical behavior of BPA at a gold | 0.1 M sodium perchlorate electrode. During the cycling of the electrode potential an adherent thin polymer layer was formed on the electrode. The film buildup process was followed in situ with an electrochemical quartz crystal microbalance (EQCM) and ex situ by electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) was used for the study of the structure/morphology of the deposited polymer coating. The results imply that polymerization and degradation of the BPA monomer may occur simultaneously during its electrochemical oxidation.

This work studies the electrochemical properties of cathodic materials for lithium–ion batteries based on mixed lithium–iron–manganese phosphate LiFe0.4Mn0.6PO4 (LFMP) obtained using a conducting binder containing poly-3,4-ethylenedioxythiophene : polystyrenesulfonate (PEDOT:PSS) and carboxymethyl cellulose (CMC). The results are compared with those for the material based on LiFe0.4Mn0.6PO4 manufactured with the conventional polyvinylidene fluoride (PVDF) binder. The electrode material with the PEDOT:PSS/CMC binder manifests enhanced functional characteristics as compared to electrodes with the conventional binder. It is found that replacement of the conventional binder by the combined conducting PEDOT:PSS/CMC binder in the LFMP-based cathodic material results in an increase in the specific capacity of the cathodic material. Particularly noticeable advantages of the material with respect to specific capacity are observed at high currents (up to 10 C), which can be explained by the increasing rate of the processes of material recharge due to a significant decrease in the charge transfer resistance and an increase in the apparent diffusion coefficient of the lithium ions.

Structurally different bis(imino)copper(i) complexes were prepared in a highly modular manner and utilized as copper-based photocatalysts in the ATRA reactions of styrenes and alkyl halides. The new photocatalysts showed good catalytic activity and ensured efficient chemical transformations.

The properties of poly(3,4-ethylenedioxythiophene) (PEDOT) films were studied electrochemically at high positive potentials (from–0.3 to 1.5 V relative to the Ag/AgCl electrode). A cyclic voltammetry (CV) study revealed the range of potentials (up to 1.3–1.5 V) where the cycling leads to significant changes in the electrochemical, structural, and morphological properties of the polymer film due to overoxidation. When the upper cycling potential Eup exceeded 1.4 V, the anodic current significantly increased during the first cycle and then decreased, which suggests a loss of the electroactivity of the polymer and degradation of its properties. In the high-frequency region of the impedance spectra of the PEDOT films, a semicircle appears after overoxidation, which indicates a notable increase of the charge transfer resistance in the system, in contrast to the films subjected to potentiodymanic processing in a limited range of potentials from–0.3 to 1.3 V. The effect of overoxidation on the polymer morphology was studied by scanning electron microscopy. The chemical state of elements in the structure of the polymer film was determined by X-ray photoelectron spectroscopy. The obtained data indicate that–S=O groups formed at the thiophene sulfur in the polymer.

Electrochemical behavior of poly-3,4-ethylenedioxythiophene composites with manganese dioxide (PEDOT/MnO2) has been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance at various component ratios and in different electrolyte solutions. The electrochemical formation of PEDOT film on the electrode surface and PEDOT/MnO2 composite film during the electrochemical deposition of manganese dioxide into the polymer matrix was gravimetrically monitored. The mass of manganese dioxide deposited into PEDOT at different time of electrodeposition and apparent molar mass values of species involved into mass transfer during redox cycling of PEDOT/MnO2 composites were evaluated. It was found that during the redox cycling of PEDOT/MnO2 composite films with various MnO2 content, the oppositely directed fluxes of counterions (anions and cations) occur, resulting in a change of the slope of linear parts of the Δf–E plots with changing the mass fraction of MnO2 in the composite film. Rectangular shape of cyclic voltammograms of PEDOT/MnO2 composites with different loadings of manganese dioxide was observed, which is characteristic of the pseudocapacitive behavior of the composite material. Specific capacity values of PEDOT/MnO2 composites obtained from cyclic voltammograms were about 169 F g−1. The specific capacity, related to the contribution of manganese dioxide component, was about 240 F g−1.

The removal of mono- and dichlorobenzenes from model solutions containing four chlorobenzene compounds separately or all four mixed, as well as mixed but with the addition of groundwater matrix was studied applying ferrate and thermally activated persulfate treatments. The concentration of target molecules were determined by gas chromatographmass spectrometer system following the enrichment of analytes by solid phase micro-extraction. At optimized experimental conditions and with the same concentration of oxidative agents, the removal efficiency values were the highest for the 1.2-dichlorobenzene (1.2-DCB) and monochlorobenzene (MCB) in case of ferrate and persulfate treatment, respectively. At nearly the same molar ratios, the persulfate treatments in comparison to the ferrate technology resulted in a higher average removal efficiency for the four target molecules in the model solutions (39 vs. 19%). However, in the presence of groundwater matrix with a given bicarbonate and chloride ion content, the average removal efficiency values reached only 14% for both treatment procedures. This means that the persulfate treatment is more sensitive to the presence of interfering ions existing in groundwater.

Many electrochemical systems are intrinsically nonstationary and are affected by time-dependent phenomena. The requirement of stationarity in the classical version of impedance spectroscopy appears to be in conflict with the essential properties of the object, therefore a post-experimental mathematical/analytical procedure is necessary for the reconstruction of the “true” impedance values. In this study, it has been shown that the 4-dimensional analysis method, originally proposed by Stoynov, can not only be used for the correction of existing (experimentally measured) impedance data, but it also opens up the possibility of the estimation of impedance spectra outside the time interval of the measurements. As an illustrative example the method has been applied for the determination of the charge transfer resistance ( R ct ) of poly(3,4-ethylenedioxytiophene) (PEDOT) modified electrode as a function of time, including the R ct value corresponding to the time instant just after overoxidation of the polymer film. After the overoxidation the charge transfer resistance decreased continuously with experiment time to a value somewhat higher than the R ct of the pristine electrode. The results imply that a “healing process” may occur at the film/substrate interface. A better understanding of this effect may have an impact on practical applications.

The subject of this paper is electrical cross-talk, an interference between the current/voltage characteristics of the two working electrodes in four-electrode (generator/collector) systems. Cross-talk arises in electrochemical cells of finite resistance due to the superposition of the electrical fields of the working electrodes, and often causes difficulties in the interpretation of measurement results. In this paper, we present an algorithm for modelling simple generation/collection experiments with a rotating ring–disk electrode (RRDE) immersed into a finite resistance solution of a redox couple. We show that based on the analysis of the Kirchhoff (Laplace) matrix of the simulation mesh, the effect of electrical cross-talk may be accounted for in such experiments. The intensity of cross-talk is found to be heavily influenced by the selection of the reference point for potential measurements; in practice, this is the position of the reference electrode or the tip of the Luggin probe. The devised model is validated by means of a simple and demonstrative experiment.

In this study trichloroethylene (TCE) removal from model solutions and groundwater by ferrate treatment was investigated applying different initial TCE concentrations, ferrate dosages and pH values. TCE concentrations were measured both in the vapor and liquid phases of water samples with head space gas chromatograph mass spectrometer (HS/GC–MS) and solid phase micro-extraction gas chromatograph mass spectrometer (SPME/GC–MS) systems, respectively. Analytical data obtained by these methods were in good agreement and the deviations changed only in the range of 1% and 7%. The optimum pH value for the ferrate treatment was pH = 7. Applying ferrate in concentration of 50 mg/L for treatment of model solutions with TCE concentration of 0.1 and 1.0 mg/L (FeO42 −/TCE molar ratios 500 and 50), the removal efficiency values were 97% and 74%, respectively. However, in case of groundwater having the same TCE concentrations with an additional 28 mg/L organic carbon content, the removal efficiency decreased to 42% and 36%. This means that the necessary ferrate dosage considerably depends on the chemical composition of the contaminated groundwater to be treated.

In this work we have investigated the electrochemical deposition of tungsten oxide into different conducting polymer films from the metastable acidic solution of isopolytungstate. Two different in the nature conducting polymer (CP) materials, namely, poly-3,4-ethylenedioxythiophene (PEDOT) and poly-3,4-ethylenedioxypyrrole (PEDOP) were used as electrode substrates for electrodeposition. Electrodeposition of tungsten oxide into freshly prepared conducting polymer films was performed by two electrochemical methods: potentiostatic and potentiodynamic. The electrochemical behavior of CP/WO3 composites, obtained with variation of synthesis conditions, was investigated by cyclic voltammetry in 0.5 M sulfuric acid. The comparison of electrochemical properties of composites allows to conclude on the mechanism of WO3 deposition. It was shown that precipitates of WO3 in CPs, electrodeposited by potentiodynamic method, display very symmetrical and sharp peaks of the redox transformation of WO3, which are rarely reported for tungsten oxides. The effect of electrochemical deposition method on the growth of WO3 precipitates on conducting polymer film electrodes and the electrochemical properties of composites was also investigated by combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The role of polyoxotungstate anion species trapping in CPs during p-doping process and facile formation of tungsten oxide nanostructures in CPs matrix is considered. A mechanism for the electrodeposition of tungsten oxide into PEDOT and PEDOP polymers was proposed.

The use of rotating ring–disk electrodes as generator-collector systems has so far been limited to the detection of Faradaic currents at the ring. As opposed to other generator-collector configurations, non-Faradaic detection has not yet been carried out with rotating ring–disk electrodes. In this study, a.c. perturbation based detection for measurement of the ring impedance is introduced. By using a conducting polymer-modified disk electrode in combination with a bare gold ring as a model, it is shown that the measured ring capacitance correlates with the polarization of the polymer film, most probably due to counter-ion exchange. A method of calculating the ring capacitance based on a small-signal sinusoid perturbation is described and the most important instrumental limitations are identified.

Inherently conducting polymers have been of great interest to scientists since the initial discovery of polymers with metal-type conductivities, and this is currently one of the most active areas of research in polymer science and engineering. Conducting polymers are attractive materials for use in a variety of applications that require materials which are both electrically conducting and mechanically compliant. It is known that poly(3,4-ethylenedioxythiophene), often abbreviated as PEDOT, is relatively stable compared to other conducting polymers. The electropolymerization of 3,4-ethylenedioxythiophene is usually carried out in organic solvents due to the low solubility of the monomer in water. However, since organic solvents are often harmful to health and uneconomical compared to water, there is a growing interest in the preparation of PEDOT films in aqueous media. In the present study, the most important electrodeposition methods for the preparation of PEDOT films in surfactant-free aqueous media are summarized. It is obvious that the stability of polymer films is of great importance for their practical application. For this reason, results of recent studies on the electrochemical stability and degradation properties of PEDOT films electrodeposited from aqueous solutions are summarized, with particular emphasis on the structural changes induced by overoxidation and oxidative (electrochemical) degradation. Experimental techniques suitable for monitoring the degradation process have been discussed, and the morphological changes in PEDOT films during overoxidation have been analyzed. Overoxidation mechanisms proposed in the literature have been surveyed.

Electrochemical and morphological properties of thin poly(3,4-ethylenedioxy-thiophene) (PEDOT) films de- posited on gold were investigated in aqueous sulfuric acid solutions. X-ray diffraction and electron microscopy were used for monitoring the morphological changes and structure evolution caused by overoxidation. The diffraction peaks of PEDOT became sharper and more intensive during the sub- sequent oxidation cycles. This indicates that besides the deg- radation of the PEDOT film, its crystallinity was gradually improved with increasing the number of oxidation cycles. These changes may result in the appearance of novel proper- ties that may be advantageous for specific applications.

The simultaneous perturbation of the disk and ring electrode potentials of an RRDE with time-varying controlling waveforms seems to be an effective way of carrying out high-sensitivity collection experiments. The method of dual cyclic voltammetry (i.e. applying dynamic potential programs to the disk and the ring electrodes of an RRDE simultaneously) has proven to be an especially promising method for studying the mechanisms of electrochemical processes. The new 3D representation of the data can be effectively used in order to reveal the formation of electroactive species in the disk electrode process. However, some issues concerning the application of this method may also arise. The “dual dynamic” perturbation of the electrodes can cause transients to appear in the current–potential characteristics of the two electrodes, which often results in electrical cross-talk effects. In this paper it is shown that the afore-mentioned cross-talk (experienced mainly when perturbations of a high rate are applied) is caused by the common resistance shared by the current paths of the two working electrodes. Numerical simulations as well as experiments with a simple model system have been carried out in order to study the cross-talk effects, and a method is suggested for their elimination.

Based on the cutting-edge technology provided by National Instruments' data acquisition cards and on the LabVIEW graphical programming language, a new electrochemical measuring system has been designed, developed, and presented in this paper. The main objective of the development was to design a workstation which is capable of conducting advanced rotating ring-disk electrode experiments that are based on the simultaneous dynamic potential control of both the disk and the ring electrodes. Our system provides great flexibility in defining the perturbing waveforms and visualizing the measured data. By the use of this system, several new experimental methods have been developed; for example, the construction of three dimensional maps of electrode reaction products has become possible.

This study is intended to give a brief overview of some of the mathematical concepts and techniques relevant to the study of thermodynamics, including the theory of homogeneous functions and partly homogeneous functions, Euler’s theorem, and Legendre transformation. The basic thermodynamic functions of an ideal monatomic gas (fundamental relations and thermodynamic potential functions) have been selected as illustrative examples.

Electrochemical, mechanical and morphological properties of thin poly(3,4-ethylenedioxy-thiophene) (PEDOT) films deposited on gold were investigated in aqueous sulfuric acid and sodium sulphate solutions. At sufficiently positive electrode potentials overoxidation of the polymer took place and resulted in morphological changes and structure evolution. These effects were monitored by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray diffraction. Significant changes in the film stress caused by overoxidation were detected by using the electrochemical bending beam method. Results of the EIS measurements proved that the charge transfer process at the metal/film interface is more hindered in case of the degraded film. According to SEM images the overoxidation/degradation of PEDOT films can result in random-like but quite well-ordered arrays of islands and trench-like structures. The diffraction peaks of PEDOT became sharper and more intensive during the subsequent oxidation cycles indicating an increase in the degree of crystallinity of the polymer.

Electrochemical and mechanical properties of thin poly(3,4-ethylenedioxythiophene) (PEDOT) films deposited on gold and platinum have been investigated in aqueous sulfuric acid solutions. At sufficiently positive electrode potentials overoxidation of the polymer takes place on both metals. Structural changes of the polymer layer caused by overoxidation (degradation) could be detected by using the electrochemical bending beam method. The impedance spectra recorded after overoxidation differed considerably from the impedance spectra of freshly made electrodes. The most interesting feature was the appearance of an arc (or a “depressed semicircle”) at high frequencies in the complex plane impedance plot, which indicates that the charge transfer process at the metal/film interface is hindered by the degradation process. Changes of the effective mass of the film were studied by electrochemical quartz crystal microbalance (EQCM). The morphological changes of the PEDOT film during overoxidation were analyzed by scanning electron microscopy (SEM).

The dual cyclic voltammetry technique and the electrochemical measuring system with rotating gold disk-gold ring electrodes have been tested in air-saturated and deaerated aqueous sulfuric acid solutions (selected as model systems). The oxygen reduction process has been chosen as model reaction. A new 3D representation of the data has been proposed which can be used to reveal the formation of electroactive species (intermediates or products) at the disk. Keywords: Dual cyclic voltammetry, Rotating ring-disk electrode, Oxygen reduction, 3D map

Electrochemical and mechanical properties of thin poly(3,4-ethylenedioxythiophene) films deposited on gold have been investigated in aqueous sulfuric acid and sodium-sulfate solutions. It has been shown that at sufficiently positive electrode potentials, overoxidation of the polymer takes place. In some cases, only small changes could be observed in the shape of cyclic voltammograms taken in the “stability region” before and after overoxidation. In contrast to this, the impedance spectra recorded after overoxidation differed considerably from the impedance spectra of a freshly made electrode. Morphological changes of the polymer caused by overoxidation (degradation) could be detected by using the bending beam method.

Several γ-valerolactone (GVL) based solvents including methyl 4-methoxyvalerate (1a), ethyl 4-ethoxyvalerate (1b), tetramethylammonium 4-hydroxyvalerate (2a), tetrabutylammonium 4-hydroxyvalerate (2b), and cholinium 4-hydroxyvalerate (2c) were prepared and characterized.

The reduction of ClO4− ions in acid media was studied at smooth polycrystalline rhodium electrodes by voltammetry, chronoamperometry and impedance spectroscopy. On the basis of the experimental results, a new mechanism for the electrocatalytic reduction of ClO4− ions has been proposed. According to this reaction scheme, the reduction process is starting with the adsorption of perchlorate ions at free active sites on the metal surface. It is also assumed that the whole process starting from perchlorate ion occurs on the surface and the role of desorption of intermediates can be neglected. On the basis of the kinetic model an expression has been derived for the impedance of the electrode, which fits the experimental data quite well.

Impedance analysis of electrochemically prepared WO3 films has been carried out in order to investigate the applicability of the diffusion-trapping model to the analysis of impedance spectra related to electrochemical hydrogen insertion. The impedance spectra measured under different conditions have been analyzed by using CNLS fitting. It has been shown, that the expressions derived for the diffusion-trapping model adequately describe the impedance response of the system. Despite of the great number of adjustable parameters many of them could be determined with a good statistics, and reasonable estimated mean values have been obtained for the others. The reliability of the estimated parameters was checked by comparing the results with existing experimental data. Keywords: Electrochemical impedance, Diffusion-trapping model, CNLS fitting, WO3 films

This study is intended to give the reader a brief overview of the mathematical background to the thermodynamic theory of surfaces and interfaces. Some general aspects of the thermodynamics of systems with interfaces are discussed, and a concise treatment of interfaces within the framework of classical thermodynamics is provided. First, to introduce the reader to the topic, a reasonably simple thermodynamic treatment of interfaces, together with a brief description of the models widely used in the literature, is presented, the characteristics of the Gibbs “dividing plane” model and the Guggenheim “interphase” model are outlined, and a derivation of the Gibbs adsorption equation is given. In the subsequent sections, several important mathematical concepts (e.g., theory of homogeneous functions and partly homogeneous functions, Euler’s theorem and the Gibbs–Duhem equation, Legendre transformation) and various functional relationships of the thermodynamics of surfaces and interfaces are summarized, with particular attention to some alternative formulations. Some of the mathematical principles and methods are explained using illustrative examples.

In the "brush model" of polymer modified electrodes it is assumed that the polymer film consists of short and long polymer chains forming bundles in such a way that only a small part of the metal substrate surface is covered by the polymeric material. The results of electrochemical impedance spectroscopy, cyclic voltammetry and surface stress measurements confirm that a brush-like ordering of the polymer chains on the metal surface is a realistic description of the surface film structure. Physicochemical parameters obtained from electrochemical impedance spectra for poly(o-phenylenediamine) films on platinum in contact with I M HClO 4 or 0.5 M H 2 SO 4 solution were analyzed on the basis of the brush model. The characteristic parameters derived from the impedance spectra of different electrodes were compared.

Experimental methods based on light beam deflection for the determination of surface stress change of electrodes are critically revisited. Expressions for the evaluation of data from electrochemical bending beam experiments with non-normal light incidence are derived. Consequences of neglecting the refraction at the optical window or at the air/solution boundary are discussed. It is shown that the data analysis in previous work needs revision, since neglecting the refraction may introduce severe errors in the calculations, and this can lead to inconsistencies in the interpretation of the experimental results.

Dissolution mechanisms suggested for Zn have been discussed. It has been shown that the anions adsorbed on the metal or metal hydroxide surfaces play an important role in the dissolution process, therefore involvement of anions in the charge and mass balance cannot be neglected. An attempt has been made to demonstrate that without taking into account the real meaning of charge transfer processes, the application of the suggested mechanism and the relevant kinetic equations may lead to serious problems in the interpretation of the experimental results.

The problem of the stability of perchlorate ions in the presence of iron group metals is discussed in the light of new experimental results obtained at various temperatures, perchlorate concentrations and pH values. Results obtained with Fe, Co and Ni were compared. It was found that the behavior of nickel in perchlorate solution significantly differs from that of Fe and Co, which have very similar and significant reactivity in the reaction with perchlorate ions. Although the reaction rate with nickel is slow, its role cannot be neglected. The reduction of ClO 4 - ions in contact with iron group metals, first of all with Fe and Co, is so pronounced that it seems inevitable to revise many statements in text-books and monographs dealing with systems containing iron group metal and perchlorates. It is suggested that electrochemists should consider the reduction process as important evidence that should be taken into account. This also involves that all experimental results and their mechanistic interpretation concerning this field should be revisited.

Simultaneous oscillations of electrode potential, surface mass and specific surface energy have been detected in the course of galvanostatic oxidation of formic acid on platinum by using a Koesters laser interferometer combined with an electrochemical quartz crystal microbalance. Changes of surface energy data measured with the electrochemical Koesters laser interferometer and with the electrochemical bending beam technique are shown to be equivalent. Problems related to the interpretation of the measured data are discussed.

Electrochemical and mechanical properties of ruthenium films electrodeposited on gold have been investigated in aqueous perchloric acid solutions. Cyclic voltammograms recorded at slow sweep rates in rotating disk experiments were highly asymmetric with respect to the electrode potential axis, and a negative current could be observed even during the positive sweep. Changes of the interfacial stress were measured by the bending beam method as functions of the electrode potential and of the concentration of chloride ions. The results are consistent with the earlier observation that perchlorate ions can be electrochemically reduced to Cl− on ruthenium. The resulting chloride ions decrease the interfacial stress and exert an inhibiting effect on the reduction process indicating the role of competitive adsorption. The desorption rate of Cl− is significantly influenced by the hydrodynamic conditions, probably through desorption/diffusion coupling. Keywords: Interfacial stress, Perchlorate reduction, Chloride adsorption, Cantilever, Bending beam method

The occurrence of the reduction of ClO4− ions in the course of the dissolution (corrosion) of Co was indicated through the study of the adsorption of radio labelled (36Cl) Cl− ions. A detailed analytical study determining the Co2+ and Cl− content of the solution phase furnished firm evidences that under suitable chosen experimental conditions the 4Co+ClO4−+8H+=4Co2++Cl−+4H2O reaction could be as important as the Co+2H+=Co2++H2 reaction considered in the literature as the only reaction path. Keywords: Cobalt, Corrosion, Perchloric acid, Reduction, Radiotracer method

The problem of the application of perchloric acid and/or perchlorate supporting electrolyte in electrochemical and corrosion studies is discussed. It is demonstrated that in contrast to the general view in the literature the reduction of perchlorate ions could be an important step in the overall process occurring in the course of spontaneous dissolution of some metals in acid perchlorate medium. It is shown that especially in the case of the dissolution of iron the reduction of ClO4− leading to the formation of Cl− plays a substantial role. Consequently, all interpretations concerning the dissolution of iron in the presence of ClO4− ions should be revisited taking into consideration the possibility of the reduction process.

Combined EQCM and voltammetric studies in conjunction with radiotracer adsorption investigations were carried out in order to obtain direct information on the interfacial behavior of the Cu 2+ –Cu system under equilibrium and dynamic conditions with the aim of clarifying the role and participation of Cu + ions formed by the interaction of cupric ions and copper metal. The appearance and accumulation of Cu + ions in the solution phase is clearly demonstrated through radiotracer experiments using labeled Cl − ions. The formation of bulk CuCl phase is preceded by the formation of a CuCl surface layer. Data obtained from combined voltammetric and EQCM studies allow us to separate the potential regimes where the electrosorption, the formation of Cu + or Cu 2+ ions, and dissolution of CuCl are the predominant processes.

The reduction of perchlorate ions at ruthenium electrodes was investigated by voltammetry, chronoamperometry, impedance spectroscopy, and by measuring changes of interfacial stress changes using the cantilever bending method as functions of electrode potential, and concentrations of perchloric acid and HCl. The cyclic voltammograms recorded at a rotating (Ru) disc electrode were highly asymmetric with respect to the electrode potential axis, and a negative current could be observed even during the positive sweep. Chloride ions decrease the interfacial stress and exert an inhibiting effect on the reduction process indicating the role of competitive adsorption. The desorption rate of Cl(-) depends strongly on the hydrodynamic conditions, probably through desorption/diffusion coupling. These results serve as a warning that in perchlorate-containing solutions in contact with Ru the adsorption of chloride ions may also influence the rate of other electrochemical processes.

Using the LabVIEW™ graphical programming language designed by National Instruments®, a digital simulation model has been developed in order to describe electrochemical processes occurring at rotating ring-disk electrodes. The model allows for taking into consideration independent potential control of the two working electrodes, homogeneous electrode reactions, as well as spatial inhomogeneities of the working electrode surfaces. The main programming concepts, as well as the operation of the simulation software is presented. Several test simulations have been carried out in order to evaluate the accuracy of the calculations.

Contradictions between views on the nature of adsorbed species in HSO 4 − SO 4 2− systems are once again discussed. It is demonstrated that adsorbed HSO 4 − and SO 4 2− species cannot be distinguished on the basis of a method proposed earlier.

Electrochemical impedance spectra are presented for Au|poly(o-phenylenediamine) electrodes in contact with 1 mol dm−3 perchloric acid solution. The roughness of the gold substrate and the film thickness, respectively, were systematically varied. The results obtained affirm that the dispersion of the low-frequency capacitance is connected with the inhomogeneity of the surface film, and the role of the surface roughness of the gold substrate is minor, if any, in the development of the CPE behaviour, which is in contrast to some hypotheses presented recently. Keywords: Electrochemical impedance spectroscopy, Polymer film electrodes, Constant phase element (CPE), Inhomogeneity, Roughness

The points raised in the paper entitled “Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates”’ have been discussed. It has been shown that, in contrast to the statements in the “Comments”, most of the papers concerning the reaction schemes suggested for the interpretation of the dissolution or deposition of metals, which were considered as a support for the opinion of the Authors of the “Comments”, support the views expressed in our original paper [J. Electroanal. Chem. 583 (2005) 148]. On the other hand, it has been stressed again that the criticism expressed in the original paper refers to dubious conclusions drawn on the basis of transient measurements.

Some problems in connection with the simulation of Cl electrosorption on Ag(1 0 0) reported in Electrochimica Acta 50 (2005) 5518 are discussed. It is concluded, that although the electrostatic model could be correct, the results of the simulation can be hardly reconciled with the experimental data owing to the contradictions discussed in the present paper.

The electrochemical reduction of the surface layer of gold oxide in sulfuric acid solutions has been investigated. Our interest in the problem arose in connection with the development and testing of an electrochemical measuring system with rotating gold disk-gold ring electrodes. With the help of the new system independent and dynamic potential programs can be applied simultaneously to the disk and the ring electrodes.By applying the “phase-shifted double cyclic voltammetry” method it could be shown that the reduction of the surface oxide layer of the polycrystalline gold disk immersed into sulfuric acid solutions is accompanied by the formation of soluble, electroreducible gold species which can be detected on the ring electrode. Keywords: Gold, Ring-disk electrode, Cyclic voltammetry