0000000000009836
AUTHOR
Francisco Vicente
The role of lithium, perchlorate and water during electrochemical processes in poly(3,4-ethylenedioxythiophene) films in LiClO4 aqueous solutions
Abstract Thin films of poly(3,4-ethylendioxythiophene) (PEDOT) were electrochemically deposited on gold electrodes in aqueous media. The role of perchlorate, lithium, and water during the charge/discharge of PEDOT films was investigated by cyclic voltammetry together with EQCM, vis − NIR spectroscopy, and acoustic impedance, also by means of ac-electrogravimetry in a 0.1 M LiCl O 4 aqueous solutions. In this way, it has been possible to correlate the electrical, mass, color and electromechanical properties changes during the electrochemical reactions of this polymer. Both, hydrated lithium cations and perchlorate anions can act as counterions during the electrochemical reactions, however, a…
An approach to the electrochemical activity of poly-(phenothiazines) by complementary electrochemical impedance spectroscopy and Vis–NIR spectroscopy
Abstract The electroactivity of two poly-(phenothiazine), the poly-(Azure A) and the poly-(Methylene Blue), has been compared in this work. The spectroelectrochemical results prove clearly the existence of two electroactive moieties integrated in the polymeric lattice, the phenothiazine ring (detected by changes of absorbance at 590 and 685 nm) and the newly formed covalent links which fixes the monomers in the backbone of the polymer (detected by changes of absorbance at 460 and 875 nm). Differences in the electrochemical response of both polymers are due to differences in this covalent link. However in both polymers, the charge balance during electrochemical reactions takes place by the e…
Determination of time dependence of passive layer on nickel from instantaneous mass/charge function F(dm/dQ) in competitive passivation/dissolution conditions
Nickel metal deposited on gold electrodes was studied in the passivity range of potentials under potentiostatic conditions and in a weakly acid sulphate medium. Mass and current variations during electrochemical experiments were analysed with the help of the instantaneous mass/charge ratio (Fdm/dQ). This analysis allows to obtain the intensity current component associated to the formation of a passive layer of Ni(OH)2, and, in this way, the experimental thickness growth. These experimental findings have been fitted to a theoretical model based on the point defect model theory for obtaining the time dependence of the thickness of the passive layer during the first stages of growth of the pas…
Electrochemical impedance spectroscopy as a tool to estimate thickness in PB films
The analysis of the faradaic impedance of electroactive films provides a characteristic point from which it is possible to estimate the thickness of thin films. Thus, electrochemical impedance spectroscopy was used in this paper as a fast and easy technique to estimate this thickness. The proposed method was checked on PB films. Keywords: Prussian blue, Electrochemical impedance spectroscopy, Thickness
Electronic Perspective on the Electrochemistry of Prussian Blue Films
The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic or…
Effects of anions size on the redox behavior of poly(o-toluidine) in acid solutions. An in situ vis-NIR cyclic spectroelectrogravimetry study
International audience; The combination of different in situ techniques allows a more complete analysis combining several physical and chemical processes of polymer-modified electrodes to be obtained. The hybrid technique -cyclic electrogravimetry coupled with visible-near infrared spectroscopy- was used to study in depth the electrochemistry of poly(o-toluidine) (POT) thin films. In this work, a POT modified electrode was polarized between the pernigraniline and leucoemeraldine forms in 0.5 M HNO3 and 0.5 M HClO4 solutions. The electrochromic properties of View the MathML sourcePOT-CIO4− and View the MathML sourcePOT-NO3− were localized in the experimental potential range associated to the…
Interfacial role of Cesium in Prussian Blue Films
The simultaneous measurement of current, mass, motional resistance and absorbance magnitudes allows the electrochemical cation insertion process to be explained during successive voltammograms around the Prussian Blue ⇄ Everitt's Salt system in CsCl aqueous acid solutions. Two different ways for the entrance of cesium to the porous structure of Prussian Blue have been observed. Firstly, Cs+ is spontaneously absorbed as CsCl into the interstitial cluster of water of the channels formed by the Fe(II)low spinCNFe(III)high spin structural units of the crystal. This chemical absorption involves a spontaneous substitution of inner water molecules of the interstitial water cluster. Finally, Cs+ …
Alternating current electrogravimetry of copper electrodissolution in a sulfuric acid solution
Abstract Copper electrodissolution processes have been studied by means of electrochemical impedance spectroscopy and ac-electrogravimetry (mass impedance). During ac-electrogravimetry acquisition, mass decreases or increases due to the electrodissolution or the electrodeposition of copper, respectively. As a result, this continuous mass drift makes impossible obtaining a true ac-electrogravimetry response unless a numerical correction was applied. It has been compared the electrochemical behavior of copper layers previously treated and other freshly deposited on the gold electrode of the quartz crystal microbalance. The simultaneous analysis of both impedance functions has allowed separati…
Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part I: The Tool
Technical details concerning the simultaneous acquisition of three impedance functions (electrochemical impedance spectroscopy, alternating current electrogravimetry or mass impedance, and alternating current colorimetry or color impedance) are presented. The analysis of each type of impedance function gives interesting information about the species participating during the electrochemical processes. Furthermore, obtaining three impedance functions in situ allows the crossed impedance functions to be calculated. These functions are especially useful in detecting delays between the color, mass, and electrical charge response of the system to the same perturbation, and it allows species parti…
Study of Prussian Blue (PB) films by ac-electrogravimetry: influence of PB morphology on ions movement
The electrochemical response of Prussian Blue films in NaCl solutions was studied. It was proved that the stability with cycling of PB films increased when these films are covered with a Nafion® membrane. This fact allows PB films to be studied in NaCl solutions under steady state conditions by impedance spectroscopy and ac-electrogravimetry. A model, which can explain the differences between the electrochemical behaviour of amorphous PB films and crystalline PB films in NaCl solutions, is proposed. This model is based on the hypothesis of a partial dehydration of the sodium ions before the electrochemical reactions take place, allowing the transport of sodium ions through the zeolitic chan…
Electrochemical behaviour of Nafion®+cupromeronic phthalocyanine films
Abstract The surface of indium tin oxide (ITO) and graphite+polymer composite electrodes can be modified by Nafion ® films containing a little amount of dispersed electroactive substances, such as phthalocyanines. This procedure allows electroanalytical information on the electroactive deposited substance to be obtained. The preparative methods of these type of modified electrodes are discussed from voltammetric results in this work. The proposed equivalent circuit explains the voltammetric differences between these electrodes. The Nafion ® net acts as a permeable membrane to the hydrogen ions. Besides, the presence of methylviologen within the Nafion ® film makes the electron transport thr…
An Electronic Perspective On The Electrochemical Changeover In Prussian Blue-Like Materials
Derivative voltabsometric scans together with previous electrogravimetric results allow to distinguish between the different electrochemical processes due to Fe-sites located into the Prussian Blue crystalline framework and other located next to ferrocyanide vacancies. The potassium, proton and hydrated proton counterions involved in these reactions are correlated to changes in near-UV/VIS/near-IR spectra. Potassium counter-ions show two different sites for insertion: one located into the crystalline framework and the other into ferrocyanide vacancies. From the monitoring of electroactive Fe-sites, it is possible to assume that the reduction of all Fe-sites located next to ferrocyanide vaca…
Quantification of electrochromic kinetics by analysis of RGB digital video images
A new, rapid, and practical procedure to obtain quantitative kinetic information of electrochromic materials is proposed. When the transition between two colors on a colored electrode surface is monitorized by digital video, the analysis of pixel color intensity (I) in sequential RGB digital images allows us to precise the half-life time (t1/2) of the color change since a maximum value of the standard deviation of the pixel intensity (σ(I)) is reached. We simulated and analyzed the evolution of standard deviation during an electrochromic transition in different circumstances (kinetic and diffusion control). As an example of application, electrochromic transitions of a thin film model, the P…
Mass/charge balance as a tool to estimate dimensional change in polypyrrole-based actuators
The deconvolution of the voltammograms of polypyrrole electrochemistry has proved to be possible through the electrochemical quartz crystal microbalance data using the F(dm/dQ) function. This deconvolution allows the evolution of the thickness of the polypyrrole films during their redox processes to be estimated and therefore, the mechanical contraction/decontraction of this polymer as a function of the ionic exchange processes can be evaluated. Keywords: Polypyrrole, EQCM, Thickness change
Kramers–Kronig transformation, dc behaviour and steady state response of the Warburg impedance for a disk electrode inlaid in an insulating surface
Abstract As the frequency approaches zero, the impedance described by the Warburg function tends to infinity. This means that the resistance of the equivalent circuit representing the electrochemical process has an infinite resistor and then the current cannot flow through it. This asymptotic behaviour also prevents the application of the Kramers–Kronig transformations, a set of integrals which should be fulfilled by any linear system. Using a more general expression of the impedance for a disk electrode inlaid in an insulating surface developed by Fleischmann and Pons (J. Electroanal. Chem. 250 (1988) 277), the Warburg impedance can be deduced and the Kramers–Kronig transformation is possi…
Surface structure determination by SEM image processing and electrochemical impedance of graphite+polyethylene composite electrodes
Abstract The electrochemical impedance behaviour of heterogeneous or/and rough electrodes has usually been associated with some geometrical parameters of the surface structure or to a statistical description of the surface properties. An experimental method for sample preparation of graphite + polyethylene composite electrodes based on plasma etching is proposed. After plasma etching, the statistical properties of the electrode, such as the graphite particle size distribution and fractional coverage are measured from scanning electron microscopy pictures using image processing software. The statistical information obtained for the surface is combined with impedance equations of independent …
Usefulness of F(dm/dQ) Function for Elucidating the Ions Role in PB Films
The conversion process of "insoluble" prussian blue (PB) films into the "soluble" structure has been followed by the simultaneous measurement of current and mass changes during voltammetric experiments and focusing on the possibilities of the use of the instantaneous mass/electrical charge ratio at each potential. A similar procedure was used for the analysis of the mechanism of reduction of PB films to the Everitt's salt form and to follow the partial dissolution of iron species during the oxidation to the prussian yellow form. The possibility of covering PB films by Nafion membranes, which make difficult the transport of anions through it, allows us to discern the role of anions in the so…
Identification of electroactive sites in Prussian Yellow films
Abstract Prussian Blue films were electrogenerated on the surface of the transparent ITO electrodes. The electrochemical oxidation to the Prussian Yellow form was investigated by means of in situ voltammetry and vis–NIR spectroscopic techniques. Changes of the whole spectra between 400 and 950 nm were analyzed and three characteristic wavelengths were selected to in situ follow the electrochemical changes of the films. Voltammetric peaks and absorbance derivative curves at these three wavelengths were deconvoluted and were interpreted such as the overlapping of different electrochemical processes. The correlation between these overlapped processes has allowed proposing three different elect…
Correlationship between microscopic observations and electrochemical behaviour of different kind of galvanized steel.
Zinc anodic dissolution has been studied according to the steel galvanized method by means of the electrochemical impedance spectroscopy (EIS) and microscopic observations. Relevant information on the galvanized method is provided by the analysis of experimental data. The galvanized method has no influence on the kinetics parameters of the zinc anodic dissolution process. The galvanized method only changes the surface texture of the working electrode. Thus, the EIS fitting allows to calculate the fractal dimension of the surface of the working electrode.
Ionic and Free Solvent Motion in Poly(azure A) Studied by ac-Electrogravimetry
International audience; This work is focused on the mechanistic aspects of the redox behavior of poly(azure A) taking advantage of the controlled modulation of their oxidation states by ac-electrogravimetry. The originality of this technique is its ability to discriminate between cation and anion involved in the charge compensation process and the accompanying free solvent transfer, directly or indirectly. Two processes were proposed where the faster ionic exchange is considered to be the participation of the anion species acting as counterions whereas the slower one is related to the proton transfer. The proton is implied as reactants for the two electroactive sites identified in the polym…
Correlation between the fractal dimension of the electrode surface and the EIS of the zinc anodic dissolution for different kinds of galvanized steel
The roughness of the working electrode is one of the factors that affects the electrochemical impedance spectroscopy (EIS) data of the zinc anodic dissolution process. The fractal dimension of digital images of shooping plate, hot dip galvanized steel, continuous hot-dipped galvanized steel and electro-galvanized steel are related with their respective EIS data. Keywords: EIS, Fractal dimension, Roughness, Galvanized steel, Corrosion
Kinetics of zinc anodic dissolution from the EIS characteristic points
A possible faradaic impedance function for the complex mechanism of metals electrodissolution across two consecutive electrotransferences has been developed in this work. The analysis of this function provides some characteristics points from which it is possible to calculate kinetic parameters of these processes. The dependence of these parameters on the potential has been studied in the case of Zn. These ones have been interpreted in terms of changes in the controlling stages of the overall rate of reaction. Keywords: EIS simulation, Zinc anodic dissolution, Kinetic constants and electron transfer
Growth of passive layers on nickel during their voltammetric anodic dissolution in a weakly acid medium
Abstract Quartz crystal microbalance in combination with voltammetry has been used for studying the electrochemical oxidation behaviour of a nickel deposit in a weakly acid medium. The instantaneous mass/charge ratio (Fdm/dQ) analysis allows to obtain the fraction of charge consumed in the passivation process, and, that way, the experimental kinetic equation of the passive layer growth. This experimental law has been fitted to the theoretical equation derived from the point defect model theory under voltammetric conditions.
Viscoelastic potential-induced changes in acoustically thin films explored by quartz crystal microbalance with motional resistance monitoring
Abstract Viscoelastic properties of intrinsically conducting polymers depend on different factors, among them polymer structure, ionic and solvent population and film thickness. During a voltammetric cycle, electrochemical reactions involve changes of these factors. Consequently, the viscoelastic properties are expected to be changed. Electrochemical quartz crystal microbalance with motional resistance monitoring were employed to calculate the instantaneous resonant frequency/motional resistance ratio (d f r / d R m ) during the electrochemical processes of acoustically thin films of poly(o-toluidine). d f r / d R m is defined as the energy dissipation factor and shows values around ∼10 Hz …
Voltammetric behavior of berenil.
Abstract Berenil is reduced on mercury drops electrode in buffered aqueous media. The reduction of —N=N— group is controlled by diffusion. Polarographie waves are of analytical usefulness. The hydrogen discharge is favored by the basic centers of the molecule in Co(ll)/ammonia-buffered media.
Electrochemical behaviour and electrical percolation in graphite-epoxy electrodes
The electrochemical properties of mouldable graphite-epoxy composite electrodes have been studied as a function of graphite content. The shape of ferri-ferrocyanide voltammograms relates to the ratio of graphite and an adsorption process. The dielectric constant from spectroelectrochemical impedance measurement of this composite electrode is maximum when the proportion of graphite is ca. 60 wt%. An electrochemical equivalent circuit is proposed. The graphite-epoxy composite acts as a multi-microelectrode near this proportion.
Effect of Anions and Oxygen on the Kinetics of the Anodic Dissolution of Nickel
An electrochemical impedance spectroscopy study on electrochemical dissolution and active/passive transition of polycrystalline nickel in acid media has been performed in sulfate and nitrate aqueous solutions. Oxygen favors the nickel electrodissolution in a nitrate aqueous acid medium, but the dissolution decreases in the sulfate medium due to nickel passivation. The anion and oxygen effect is analyzed from a model where Ni(I) species are stabilized on the Ni metal surface and all anions present in the solution compete in the neutralization of Ni(I) and Ni(II) and in the solubilization of Ni(II).
Effects of anion size on the electrochemical behavior of H2SO4-structured poly(o-toluidine) films. An ac-electrogravimetry study in acid solutions
International audience; ac -Electrogravimetry has allowed an easy separation of kinetic information to be evaluated for all the transferred species in three different H2SO4-structured poly(o-toluidine) or POT films, View the MathML sourcePOT-NO3−, View the MathML sourcePOT-ClO4− and POT-Cl− films when they are polarized between the pernigraniline (oxidized) and leucoemeraldine (reduced) forms. It is clear that larger anions slow down the electrochemical transitions of POT films, but the effects of anion transfer on hydrated protons and free solvent transfers are affected. For the same polymeric structure of a POT film, the kinetics of all specie transfers have been evaluated considering the…
The role of inner counterions within PB films during electrochemical processes
Abstract The shape of voltammograms of Prussian Blue films (ferric ferrocyanide, PB) deposited on ITO (indium–tin oxide) electrodes in aqueous KCl, CsCl and NH 4 Cl solutions has been studied. These results proved a double role of countercations during these electrochemical processes. Countercations can either be only retained within the zeolitic pores of the PB structure forming part of their inner solution, or can also form part of the crystalline structure of PB films by replacing some iron sites. The different electrochemical behaviour of PB films in the three studied solutions (KCl, CsCl and NH 4 Cl) is analysed from this point of view.
Quartz Crystal Microbalance And Electrical Impedance Characterization Of Nickel Dissolution Process.
Abstract. The anodic nickel dissolution in acid media is analysed by means of EQCM and EIS techniques. The experimental impedance spectra have been fitted to the equivalent circuit which corresponds to two consecutive electron transfers followed by a Ni(II) desorption. That way rate constants and surface concentrations of the Ni(0) and Ni(I) species are obtained. EQCM also provides information about the mechanism of deposition and passivation of nickel as well as the hydrogen evolution.
Electrochemistry and electrocatalysis of a Pt@poly(neutral red) hybrid nanocomposite
Abstract Platinum nanoparticles have been deposited on a scaffold of electrosynthetized phenazine-type polymer, the poly(neutral red). This work discusses the role of poly(neutral red) in the electrochemistry and electrocatalysis properties of the hybrid nanocomposite. In situ combination of electrochemical quartz crystal microbalance and visible-near infrared spectroscopy (cyclic Vis-NIR spectroelectrogravimetry) and a combination of electrochemical impedance spectroscopy and mass impedance spectroscopy ( ac -electrogravimetry) were employed. Two electrochemical processes have been identified in our experimental conditions. On the one hand, the radical cations (polarons) localized in the i…
EIS and Ac-electrogravimetry study of PB films in KCl, NaCl, and CsCl aqueous solutions
Prussian Blue films have been studied by means of ac-electrogravimetry, electrochemical impedance spectroscopy, and electrochemical quartz crystal microbalance in different aqueous salt solutions. Impedance data was interpreted in terms of a model based on a potential drop at the electrode/film interface and a potential drop at the film/solution interface. Quantitative results obtained by the fitting of impedance and ac-electrogravimetry allow to conclude that the main contribution to the potential drop at the film/solution interface is due to the dehydration-hydration process of cations on entering or leaving the film.
Voltammetric behaviour of monomeric fac-trioxomolybdenum(VI) complexes with aminocarboxylic ligands in aqueous media
Abstract Cyclic voltammetry, polarography and controlled-potential coulometry experiments have been used to characterize the electrochemical reduction of fac-MoO3L2− complexes (L = aspartic acid or iminodiacetic acid) in aqueous media. These complexes are reduced in two irreversible proton-assisted steps to give an oxo-bridged molybdenum(V) species and then to a molybdenum(III) dimer species. At pH 4.5, the former reduction step for the iminodiacetic acid ligand occurs at Ep = −0.75 V, while the second one appears at −1.12 V vs SCE. The overall electrochemical process can be described in terms of a homogeneous chemical reaction, coupled between two electron transfers (ECE mechanism), that i…
Kinetics of Surface Chemical Reactions from a Digital Video
In the last few years, the color analysis of the studied surface has been regarded as a nonexpensive way to obtain not only the spectrochemical data but also the spatiotemporal information of the entire surface. Mean color intensities and standard deviation calculated from the red, green, and blue color histograms of digital images of surfaces have been considered particularly useful for the chemical understanding of surface kinetics. The shape of curves, the maximum of peaks, or the half-peak widths depend on the kinetic constants and on the kinetic order of the surface chemical process. Some strategies used for obtaining the kinetics from RGB color intensities and their standard deviation…
Identification of Processes Associated with Different Iron Sites in the Prussian Blue Structure by in Situ Electrochemical, Gravimetric, and Spectroscopic Techniques in the dc and ac Regimes
The physicochemical properties of Prussian blue films are strongly dependent on the ratio Fe3+/Fe2+ in the structure. This ratio can be modulated by electrochemical techniques such as cyclic voltammetry, and some information about physicochemical properties can be extracted from in situ auxiliary techniques. Prussian blue films have been studied by the use of in situ vis–NIR spectroscopy, quartz crystal microbalance, and electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy). By cyclic voltammetry + absorbance derivative curves + mass derivative curves, it has been possible to identify at least three different processes during the reduction of Prussian bl…
Vis/NIR spectroelectrochemical analysis of poly-(Azure A) on ITO electrode
Electrochromic behavior of poly-(Azure A) on indium–tin oxide electrode is analyzed in an aqueous potassium nitrate solution. The dependence of the absorbance on the applied potential during cyclic voltammograms proves very interesting at two selected characteristic wavelengths: at 925 nm, attributed to an intermediate species and another at 735 nm, attributed to the oxidized form of the polymer. Molar absorptivity coefficients for both species have been calculated from the relationship between current and the derivative of absorbance with respect to time. Voltammograms of formation of the intermediate are simulated from spectroelectrochemical results. Keywords: Poly-(Azure A), Spectroelect…
Electrochromic Performances of Poly(Azure A) Films from Digital Video-Electrochemistry (DVEC)
Poly(Azure A) (PAA) films doped with sodium dodecyl sulfate (SDS) were grown on transparent indium tin oxide (ITO) glass substrates by cyclic voltammetry. The electrochromism of PAA was investigated by digital video-electrochemistry (DVEC). DVEC consists of the acquisition of sequential digital images during the electro-stimulated changes of PAA color. The evolution of red, green, and blue (R, G, B) colors intensity (I) of analyzed pixels provides enough sensitivity to detect changes of some nmol cm−2 of electroactive centers. Besides, the different time evolution of these color intensities can serve to discern among different electroactive centers activated in the polymer. For the first ti…
Chronoamperometry of prussian blue films on ITO electrodes: Ohmic drop and film thickness effect
Abstract The chronoamperograms associated with the reduction of prussian blue films deposited onto indium tin oxide (ITO) electrodes to the Everitt’s salt form, are influenced by the ohmic drop effect. These chronoamperometric curves have been simulated by means of a numerical finite difference model which is able to explain their shape and their dependence on the thickness of the film and on the uncompensated resistance. An analytical expression which describes the dependence of current against time at initial times considering the ohmic drop effect has also been proved when applied to these chronoamperometric curves at short times.
Evidence of Magnetoresistance in the Prussian Blue Lattice during a Voltammetric Scan
This manuscript reports evidence of magnetoresistance effects in the Prussian Blue lattice during a voltammetric scan at room temperature. Accordingly, the PB is a well-known semiconductor that becomes surprisingly an almost metallic conductor in the presence of an internal magnetic field induced during the voltammetric scan. This offers appealing perspectives for the control of this interesting phenomenon from electrochemical techniques that could be used for the fabrication of the recent phase-change computational memories, which are electronically configurable. Herein, the PB magnetic properties have been monitored in situ by means of resonating magnetic microsensors based on the shift i…
Apparent activation energies and apparent frequency factor in polarographic waves of paludrine-Zn(II)
Abstract Arrhenius and Vlcek plots of ac 1 and dp polarograms of paludrine-Zn complexes are tested in order to understand the apparent activation energies and pre-exponential factor, and their dependence on the potential. These empirical treatments are useful for obtaining information about the energetic contributions of the elemental processes associated with the Zn(II) and paludrine ligands in the overall mechanism of reduction of the complex 2:1 on the mercury interface.
RGB video electrochemistry of copper electrodeposition/electrodissolution in acid media on a ternary graphite:copper:polypropylene composite electrode
Abstract Galvanostatic copper electrodeposition and electrodissolution on graphite:copper:polypropylene composite electrodes in acidic media have been investigated to extend the technological applicability of ternary composites. Both electrochemical processes were monitored by RGB video electrochemistry. The analysis of digital images allowed the color changes on the electrode surface to be investigated. We estimate the growth rate of the copper layer in two different electrode geometries. The relatively high resistance of this composite causes a gradient of the electric resistance along the electrode involving a non-homogeneous electrodeposit growth in CuSO4/H2SO4 aqueous solutions. Copper…
Kinetic and Mechanistic Aspects of a Poly(o-toluidine)-Modified Gold Electrode. 1. Simultaneous Cyclic Spectroelectrochemistry and Electrogravimetry Studies in H2SO4 Solutions
International audience; Electrodeposited poly(o-toluidine) (POT) on gold electrodes was investigated in a 0.5 M H2SO4 aqueous solution using cyclic electrogravimetry with in situ vis-NIR spectroscopy. This coupling of different techniques allows the electrical, color, and mass changes during the electrochemical reactions of these polymers to be correlated. Therefore, this is a powerful tool to obtain valuable information on the physical models of polymer films and their electrochemical properties. The accurate analysis of the results from these techniques showed the contribution of three different redox transitions (leucoemeraldine-polaron transition, polaron-bipolaron transition, and bipol…
Ohmic drop effect on the voltammetric behaviour of graphite + polyethylene composite electrodes
Graphite + polyethylene composites can be used as electrodes in electrochemical experiments because of their low charging current in contrast with other composite electrodes. However, the results reveal that the ohmic drop must always be considered in the data analysis. The peak potential and the peak current are related through an expression deduced for a Nernstian process where the mass transport is controlled by diffusion. The determination of the uncompensated resistance implies also the calculation of the convolution of the current.
An electromechanical perspective on the metal/solution interfacial region during the metallic zinc electrodeposition
The difficulty of studying the metal/solution interfacial region makes the use of non-conventional measurement techniques indispensable. In this way, a careful in situ study by means of acoustic impedance techniques coupled with nano-electrogravimetric techniques allowed this interface to be monitored during the metallic zinc electrodeposition process. This paper proves the formation of a viscoelastic layer consisting of ultra-hydrated Zn(II)/Zn(I) salts as a key step in the metallic zinc electrodeposition mechanism in sulfate aqueous solutions. Surprisingly, this layer is located in the metal/solution interfacial region and not on the reaction substrate. The chloride ions effect on the met…
Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates’by G.G. Láng, and G. Horányi [J. Electroanal. Chem. 583 (2005) 148–154]
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…
Insights on the Mechanism of Insoluble-to-Soluble Prussian Blue Transformation
The electrochemical transformation of the soluble form of Prussian blue (PB) material from the insoluble form was monitored using electrochemical, gravimetric, acoustic, and spectroscopic techniques simultaneously. The described combination of in situ techniques represents an innovative tool for measurement in electrochemistry, which provides complementary information on the electrochemical systems. The insoluble-to-soluble PB transformation process takes place during the successive voltammetric cycles between the mixed valence form (PB) and the fully reduced form [Everitt's salt (ES)]. One of the processes that takes place is the exit of free Fe(CN) 4- 6 ions occluded in the vacancies of t…
A kinetic interpretation of a negative time constant in impedance equivalent circuits for the dissolution/passive transition
Abstract A theoretical impedance function is proposed for the active/passive transition of nickel in an acid sulphate medium. It is considered that passivating species progressively covers the electrode surface. This approximated model predicts the appearance of negative time constants in the impedance spectra when coverage coefficient θ values for passive species are greater than 0.5.
Study by EQCM on the voltammetric electrogeneration of poly(neutral red). The effect of the pH and the nature of cations and anions on the electrochemistry of the films
Generation of poly(neutral red) films has been studied by means of the simultaneous measurements of current–potential and mass–potential curves during cyclic voltammetry (CV) experiments. It has been proved that the presence of molecular oxygen in the solution increases the amount of polymer deposited on the electrode. Otherwise, using the mass/charge ratio it is possible to obtain quantitative information about the electrodeposition by different procedures. It is observed that this ratio decreases when the amount of polymer electrogenerated increases, except when the polymer is not reduced and oxidised after its electrogeneration. The study of poly(neutral red) by CV and quartz crystal mic…
Stability of Prussian Blue films on ITO electrodes: effect of different anions
Abstract Transformation of insoluble newly deposited Prussian Blue (PB) into the soluble structure stabilizes the film and allows its total oxidation to Prussian Yellow. The stability of PB films in electrochemical processes in successive potential cycling experiments and under long-term chemical attack by an electrolyte depends not only on the cation that takes part but also on the nature of the anion present. In aqueous media, the sulphate ion clearly destabilizes the crystalline structure whereas the nitrate ion favours stabilization. Initial changes in the voltammograms recorded immediately after the spectroscopic tests have been detected in all media. During the immersion period water …
Anodic Dissolution of Nickel across Two Consecutive Electron Transfers
The analysis of the electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy results are consistent with a nickel electrodissolution process limited by the passage of Ni(I) to Ni(II), when chloride ions are present in the acid sulfate medium, or by the passage of Ni(II) to Ni 2+ in solution, in absence of chloride. This interpretation allows an explanation of the potential evolution of Fdm/dQ values in both experimental conditions by assuming the formation of a new phase on the electrode surface with a gel-like structure placed between the metal and the solution. Ni(I) surface concentration is calculated from the instantaneous mass/charge Fdm/dQ values.
Graphical Analysis of Electrochemical Impedance Spectroscopy of Two Consecutive Irreversible Electron Transfers. 1. Theoretical Study of the Anodic Dissolution of Metals
A general function for the faradaic impedance associated to a two consecutive single electron transfer mechanism followed by a irreversible first-order step has been obtained on the basis of formal kinetics. Kinetic parameters associated to this reaction mechanism can be obtained from the different kind of plots of the impedance function: Nyquist, Cole-Cole, and different Bode plots. A strategy for obtaining all parameters is suggested and analyzed on a detailed flowchart.
Electrochemical impedance spectroscopy for studying passive layers on steel rebars immersed in alkaline solutions simulating concrete pores
Present paper deals with the use of the electrochemical impedance spectroscopy to identify different processes in the passive layer growth over steel rebar surface immersed in an alkaline media simulating the concrete pore solution. Two cases have been considered: a passive layer spontaneously grown in a high alkaline media and a passive layer assisted by the application of an anodic potential in the same media. The application of electric equivalent circuits allows distinguishing between the different mechanisms occurring in this passive layer when grows in different conditions. An electric equivalent circuit with two RC loops connected in parallel is often used for fitting the EIS diagram…
An approximate theoretical impedance analysis of the anodic dissolution of nickel across nickel(II) stabilised by means of competitive anions
Abstract A theoretical impedance function for the anodic dissolution of nickel is developed by considering the hypothesis that there are two competitive anions which participate in the stabilization of the electrogenerated Ni(II) species. The experimental effect of chloride ion concentration on nickel electrodissolution process is analyzed by means of a mechanism that considers this competency. It is observed that an increased Cl − concentration causes an increase in Ni(I) surface concentration and a decrease in the kinetic constant rates of the considered mechanism. Moreover, an increased chloride concentration causes a flattening in the low frequencies inductive loop in the Nyquist plot r…
About the Insoluble to the Soluble Prussian Blue Transformation
Figure 1 shows firstly an increase of the motional resistance during the first scan of the transformation process, denoting an increase of the viscoelasticity of this structure. Soluble Prussian Blue have a localized changeover in the properties of these films just when Fe(III) fraction reaches the characteristic value. Secondly, this Figure shows an increase of motional resistance in zone 2 of the voltammetric scan, proving more evident for the last cycles than for the first ones. The increase of the motional resistance in zone 2 records an increase of the PB coercive field which at the same time, is due to an interesting changeover in the PB physiochemical properties localized at this pot…
Calculation of the surface concentration of Zn(I) from the anodic voltammetric peak of zinc combined with the QCM results
Deconvolution of voltammograms of anodic dissolution of zinc has proved to be possible through the electrochemical quartz crystal microbalance data and the F(dm/dQ) function. This deconvolution allows to calculate the surface concentration of Zn(I) and to obtain an estimation for the kinetic constant of the second single-electron transfer. Keywords: Zinc anodic dissolution, EQCM, Surface concentration, Deconvolution and kinetic constant
Polymer dynamics in thin p-type conducting films investigated by ac-electrogravimetry. Kinetics aspects on anion exclusion, free solvent transfer, and conformational changes in poly(o-toluidine)
A new transfer model is proposed to explain ac-electrogravimetry response of p-doped films. This model takes into account the exclusion effect occurring as a result of the anion transfer. The insertion/expulsion of anions inside a film involves simultaneously the expulsion/insertion of free solvent molecules. The number of solvent molecules excluded depends on the volume of anion transferred. Solvent transfer stimulated by the conformational changes of films constitutes the remaining electrogravimetric response when the exclusion process cannot explain by itself this response. Consequently, the kinetics of this free solvent transfer can be directly related to the kinetics of conformational …
Analysis of an impedance function of zinc anodic dissolution
Zinc anodic dissolution has been studied by means of electrochemical impedance spectroscopy (EIS). The kinetic study of the oxidation mechanism has allowed us to propose a theoretical impedance function for this system in deaerated sulphate medium. Relevant information on the faradaic process is provided by analysis of the theoretical impedance function. Kinetic parameters of this system can be calculated from the fitting of experimental data to the faradaic impedance function deduced theoretically. The physical measurements of this function are analysed by means of the dependence of simulated EIS spectra on kinetic parameters.
Graphical analysis of electrochemical impedance spectroscopy of two consecutive irreversible electron transfers. 2. Zinc anodic dissolution in acid media.
The graphical analysis of the impedance plots is used in the study of the electrodic systems that take place through two consecutive single electron transfers. The zinc anodic dissolution is studied by using this procedure. The characteristic points easily allow us to explain and to simulate the impedance behavior of this electrodic system according to the steady-state potential and the roughness of the working electrode. The direct procedure for parametrical identification from the graphical analysis allows us to reduce the time needed for an impedance experiment. This graphical analysis is suggested for studying thin coated galvanized steels.
Electrochemical reduction of the nitrite to ammonium ions in presence of [MoO2(O2CC(S)C6H5)2]2−
Abstract Ammonia is formed during potentiostatic reduction of sodium nitrite solutions on the nafion-complex-coated electrode. When (NH4)2[MoO2(O2CC(S)(C6H5)2)2] is present in NaNO2 solutions a polarographic wave is associated to electrocatalytic reduction of nitrite ion. The wave height varies linearly on the concentration of nitrite ion, allowing a procedure for analysing this ion. This electrochemical behaviour distinguishes the nitrite from the nitrate ions. The Mo(VI), Mo(V), and Mo(IV) are involved in catalytic redox processes determining formation of NH4+ from nitrite ions.
Singular points of electrochemical impedance function
A model of EIS response for a system with two consecutive monoelectron transfers is developed in this work. Relevant information on the mechanism of these electrochemical systems is provided by the parametrical identification of the theoretical faradaic impedance function. The kinetic parameters of this model are easily calculated through the calculus of the characteristic points of this function. This calculus allows to interpret the metals anodic dissolution according to the reaction mechanism and, therefore, allows us to establish easily the kinetic and thermodynamic behaviour of these systems with respect to any experimental parameter.
Evaluation of the electrochemical anion recognition ofNO3−-imprinted poly(Azure A) inNO3−/Cl−mixed solutions by ac-electrogravimetry
Abstract During the reversible electrochemical reactions of the intrinsically conducting polymer (ICP) films, ions are inserted in them to balance the inner charge site of the polymer. For this reason, doped ICP films with anions or cations can be good candidates for the electrochemical removal of contaminant ions from wastewater. In this work, a polymer of a phenothiazine derivative (poly(Azure A or PAA)) was electrosynthesized by cyclic voltammetry in aqueous solutions using nitrate ions as a structural template. After that, PAA film was repeatedly cycled in identical conditions in a monomer-free solution. The electrochemical anion recognition of the nitrate-imprinted poly(Azure A) ( N O …
Kinetic and Mechanistic Aspects of a Poly(o-Toluidine)-Modified Gold Electrode. 2. Alternating Current Electrogravimetry Study in H2SO4 Solutions
International audience; Electrodeposited poly(o-toluidine) (POT) on gold electrodes was investigated in 0.5 M H2SO4 aqueous solutions using alternating current electrogravimetry (simultaneous electrochemical impedance and mass transfer functions). The kinetic aspects of the three different redox transitions proposed for this polymer (leucoemeraldine-polaron transition, polaron-bipolaron transition, and bipolaron-pernigraniline transition) and the species involved, cation (hydrated proton), anion (bisulfate ion), and free solvent (water), are studied by means of the mass impedance technique. An ionic transfer model is proposed with coherent results where anion transfer is the fastest process…
Electrochemical impedance spectroscopy of conductor-insulator composite electrodes: properties in the blocking and diffusive regimes
Abstract The electrochemical response of graphite + high-density polyethylene composite electrodes as a function of the conductivity load was investigated. Percolation theory was used in order to explain the electrochemical behaviour of this type of composite electrode. In the blocking regime the electrochemical impedance of this electrode material behaved as R 0 + q · ( ω j) − η , where R 0 represents the uncompensated resistance of the cell. Its value depended on the graphite volume proportion ( ν ) with a power law R 0 ∞ ( ν — ν c ) − t with a critical exponent t = 3.2 ± 0.1 which is close to the mean field value, t = 3. With potassium chloride concentrations greater than 0.7 M, the unco…
Prussian blue films deposited on graphite+epoxy composite electrodes: electrochemical detection of the second percolation threshold
Abstract The electrochemical behavior of Prussian blue films galvanostatically electrodeposited on graphite+epoxy-resin composite electrodes was studied. The composite electrodes were prepared with different graphite proportions and their effect on electrochemical reduction of the Prussian blue was analyzed by means of the uncompensated resistance approximation and the electrical percolation theory. The results suggest that the electrode with 60% graphite reaches the second percolation threshold and its internal structure changes from a compact to a porous one. Mechanical tensile tests were performed in order to confirm the critical behavior of this material at the percolation thresholds. T…
Electrochemical behaviour of inorganic redox substances dispersed into Nafion® films
Abstract The voltammetric response of a Nafion ® film deposited on an indium tin oxide (ITO) electrode was studied. It was observed that the response is affected by the thickness of the Nafion ® layer. Also, the voltammograms show differences depending on the concentration and composition of the supporting electrolyte solution. The ITO–Nafion ® system can be stabilised by repetitive cyclic voltammetry, and then the inner hydrogen reduction is not detected by electrochemical impedance spectroscopy. Different substances were dispersed into the Nafion ® matrix in order to study their electrochemical response.
Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part II: Prussian Blue ⇆ Everitt’s Salt Process
The simultaneous recording of three impedance functions (electrochemical impedance, color, and mass impedance) allows the role of different species to be distinguished easily during electrochemical processes in conducting and electrochromic films. Herein, this technique has been applied to the study of the Prussian blue films at several potentials between the blue form (Prussian blue) and the colorless form (Everitt’s salt). At these potentials, these electrochemical reactions take place by means of exchange of different ions. Thus, the exchange of potassium cations is related to the changes of absorbance at 690 nm, whereas the exchange of protons does not introduce color changes at this wa…
Usefulness of the Instantaneous Mass-charge Ratio for Elucidating the Ions Role in the Stabilization and Dissolution Processes in Prussian Blue Films
The conversion process of 'insoluble' Prussian Blue films into the 'soluble' structure has been followed by the simultaneous measurement of current and mass changes during voltammetric experiments and focusing on the possibilities of the use of the instantaneous mass/electrical charge ratio at each potential. A similar procedure was used for the analysis of the mechanism of reduction of Prussian Blue films to the Everitt's Salt form and to follow the partial dissolution of iron species during the oxidation to the Pussian Yellow form. The possibility of covering Prussian Blue films by Nafion membranes which make difficult the transport of anions through it allows to discern the role of anion…
Simultaneous Anodic Dissolution and Passivation of Nickel in Moderate Acid Medium
The EQCM results show that nickel electrodissolution and nickel passivation occur simultaneously in a sulphate acid media of pH = 3.5. Mass balances have been done from the instantaneous F(dm/dQ) function. The fitting of the experimental i = f(E) and -dm/dt = g(E) curves to the theoretical equations allow to obtain information about the kinetic parameters and the molecular mass of the species involved in the electrochemical processes.
Oscillatory Changes of the Heterogeneous Reactive Layer Detected with the Motional Resistance during the Galvanostatic Deposition of Copper in Sulfuric Solution.
Metallic copper was galvanostatically deposited on quartz|gold resonant electrodes by applying a constant current in a 0.5 M CuSO4/0.1 M H2SO4 aqueous solution. Galvanostatic copper deposition is one of the best methodologies to calibrate the electrochemical quartz crystal microbalances (EQCM), a gravimetric sensor to evaluate changes in mass during the electrochemical reactions through the Sauerbrey equation. The simultaneous measurement of mass, current density, and motional resistance by an EQCM with motional resistance monitoring allows us to characterize the processes occurring on the electrode surface and at the interfacial regions with unprecedented detail. During the galvanostatic c…
Spatiotemporal colorimetry to reveal electrochemical kinetics of poly(o-toluidine) films along ITO surface
Abstract Sheet resistance of transparent conducting electrodes can affect dramatically the electrochromic response of surface confined active species in any electrochromic device. The generated gradient of effective potential on the electrode surface has a direct impact on the electrochemical kinetics of these species. In this work, the electrochromic poly (o-toluidine) (POT) film, a derivative polyaniline, was deposited along a narrow, long transparent indium tin oxide (ITO) supporting electrode with a sheet resistivity of 30 Ω cm−1. This configuration was used as a model to simulate a surface electrical conduction from the external metallic contact to the opposite extreme of ITO with an i…
Electrochemical behaviour of poly(neutral red) on an ITO electrode
Abstract The formation of a radical cation, by electrochemical oxidation of the neutral red dye in acidic aqueous solution, is controlled by diffusion towards the electrode surface. This is the initiation step of the electrogeneration, potentiostatic or potentiodynamic, of poly(neutral red) films on an indium–tin oxide (ITO) electrode. The polymeric film is a redox semi-conductor, and shows a microporous membrane-like character. Its electrochemical behaviour depends on the generation process. The hydrogen ions play a double role: first as reactants at electrochemical and acid–base equilibrium, second as counterions of the electrons. The global process of the electron-hopping is limited by t…
Electrochemically induced free solvent transfer in thin poly(3,4-ethylenedioxythiophene) films
International audience; In dynamic intrinsically conducting films, counterions transfer and conformational movements stimulated by the electrochemical reactions affect the free water molecules transfer. Poly(3,4-ethylenedioxythiophene) or PEDOT is included in this category. Here, p-doping of PEDOT immersed in LiClO4 aqueous solution was explored by ac-electrogravimetry. Electrochemical impedance spectroscopy combined with mass impedance spectroscopy proves useful for species identification and kinetics. For PEDOT, new equations have been developed to analyze the ac -electrogravimetry response. Quantitatively, faster free water transfer and slower coupled View the MathML sourceClO4−/free wat…
Anodic growth of passive layers on steel rebars in an alkaline medium simulating the concrete pores
Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques have been used to study passive layers anodically grown on steel rebars in an aqueous alkaline solution simulating the electrolyte of the concrete pores. Nyquist diagrams recorded by EIS at the different stabilization potentials show a diffusional tail at low frequencies. The analysis of the impedance measurements has been made by means of an equivalent circuit with a Warburg component and within the framework of the point defect model (PDM) theory. It is observed that the calculated concentration of vacancies is a function of the potential in accordance with the theoretical prediction of the PDM.
Digital video-electrochemistry (DVEC) to assess electrochromic materials in the frequency domain: RGB colorimetry impedance spectroscopy
Abstract This work is the first one allowing the characterization of electrochromic devices simultaneously at various parts on their surface and different rates of color change. We describe a new proficient and affordable methodology for reporting electrochromic parameters such as coloration efficiency, optical contrast, and switching time based on the use of digital video-electrochemistry (DVEC) in the ac regime, namely RGB colorimetry impedance spectroscopy. Simultaneously with the electrochemical impedance spectroscopy, the RGB color changes of an electrochromic electrode were recorded by a CCD digital camera at 120 digital images per second. In such conditions, RGB electrochromic change…
An electrochemical impedance and ac-electrogravimetry study of PNR films in aqueous salt media
Electrochemical impedance spectra and ac-eletrogravimetry of poly(neutral red) films are studied in different aqueous media. The dependence of these experimental data on the nature of alkaline cation and monovalent anion present in the solution and on the pH is analysed. During the electrochemical processes, it is observed that all three species—the salt cation, the salt anion and the hydronium ion—participate to balance the electrical charge within the film. It is also possible to conclude that the participation of anions takes place faster than hydronium ions participation. Besides, the relative participation of these species is related to the pH of the solution. Keywords: Poly (neutral r…
Motional Resistance Evaluation of the Quartz Crystal Microbalance to Study the Formation of a Passive Layer in the Interfacial Region of a Copper|Diluted Sulfuric Solution
A hyphenated technique based on vis–NIR spectroscopy and electrochemical quartz crystal microbalance with motional resistance monitoring was employed to investigate the dissolution of copper in acid media. Changes in motional resistance, current, mass, and absorbance during copper dissolution allow the evolution of the interfacial region of copper|diluted sulfuric solution to be understood. In particular, motional resistance is presented in this work as a useful tool to observe the evolution of the passive layer at the interface. During the forced copper electrodissolution in sulfuric solution, SO4(2–) favors the formation of soluble [Cu(H2O)6]2+. On the contrary, OH– involves the formation…
Ohmic drop of Prussian-blue/graphite+epoxy electrodes
Abstract Ohmic drop effects on the voltammogram shape of the Prussian-blue⇌Everitt’s salt system have been studied by considering the electroactive film model. As the uncompensated resistance varies, the experimental characteristic curve parameters also varies. A dependence of the voltammograms with the graphite proportion was found related with the ohmic drop due to the composite electrodes. The optimal graphite proportion to obtain a good faradaic-to-charge current ratio was 62% in weight which coincides with the second percolation threshold. The ohmic overpotential, which relates the ohmic drop with the electrochemical magnitudes, is also minimum at this proportion.
Electrochemical Quartz Crystal Microbalance Study of Copper Electrochemical Reaction in Acid Medium Containing Chlorides
Copper electrodissolution and electrodeposition were studied by means of gravimetric quartz crystal microbalance and electric cyclic voltammetry combined measurements. Relevant information on the mechanism of these electrochemical processes is provided by the analysis of experimental data and particularly of the mass change per charge unit. The copper electrodeposition and electrodissolution take place by means of two consecutive monoelectronic transfers where the anion participation in the reaction mechanism is specified. Besides, it is proved that the presence of molecular oxygen in the solution contributes to the formation of a passive layer on the surface of the metallic copper deposit.
The correlation between electrochemical impedance spectra and voltammograms of PB films in aqueous NH4Cl and CsCl
Abstract Voltammetric curves of reduction of Prussian Blue Films to the Everitt’s Salt form and oxidation to the Prussian Yellow form show important differences depending on the supporting electrolyte countercation. The rate of the overall electron-hopping depends on the countercation. Apparent diffusion coefficients are evaluated from impedance spectra at different stabilization potentials. The dependence of the apparent diffusion coefficients on the stabilization potential can help understand the dependence of the voltammograms shape on the countercation nature.
Determination of the electroactive area of graphite+polyethylene composite electrodes. Uncompensated resistance effects and convolution analysis of chronoamperograms
In this work, it is shown how the convolution analysis of chronoamperograms permits the observation of the uncompensated resistance and the natural convection effects on the electrochemical response of potassium ferrocyanide. The uncompensated resistance causes the current intensity to follow the Cottrell equation only after a certain critical time. The convolution of chronoamperograms worked out at different integration times shows a maximum when this time is long enough. The classical diffusion equations cannot explain this phenomenon themselves. The development of this maximum associated with the natural convection is discussed. If both these factors, the ohmic drop and the natural conve…
EQCM and EIS studies of Znaq2++2e−⇄Zn0 electrochemical reaction in moderated acid medium
The zinc electrodissolution and electrodeposition have been studied by means of electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy. Relevant information on the mechanism of these electrochemical processes is provided by the analysis of experimental data. The zinc electrodeposition takes place with an important participation of hydrogen ions while the zinc electrodissolution occurs, in these experimental conditions, by a mechanism in two steps. Besides, it is proved that the presence of molecular oxygen in the solution contributes to the formation of a passive layer on the metallic zinc deposit.
Use of RGB digital video analysis to study electrochemical processes involving color changes
Color changes on an electrode surface during the course of electrochemical processes were monitored by in situ digital video recording. The evolution of standard red, green and blue (sRGB) intensity channels extracted from digital images showed a close relationship with the electrochemical processes taking place. In particular, the derivative of the sRGB mean intensity with respect to time (dI−/dt) gave useful insights into the electrochemical mechanism. The standard deviation (std) of the sRGB intensity provided information about the color homogeneity of the studied region on the electrode surface. We selected poly(o-toluidine) electrochromism on a transparent electrode and anodic copper d…
A numerical approach to the voltammograms of the reduction of Prussian Blue films on ITO electrodes
The uncompensated resistance, mainly due to the ITO electrode, modifies the shape of voltammetric curves of the system Prussian Blue ⇄ Everitt's Salt films deposited on this transparent electrode. A numerical finite difference model which is able to explain the shape of these voltammetric curves is studied in this paper. This model explains the dependence of voltammetric curves on the film thickness and uncompensated resistance.
The role of potassium and hydrogen ions in the Prussian Blue ⇆ Everitt's Salt process
Cyclic voltammetry experiments have proved very useful in the knowledge and understanding of the role of the potassium and hydrogen ions during the Prussian Blue ⇄ Everitt's Salt process. While potassium ions act as a stoichiometric reactant, the hydrogen ions play a very important role in the kinetics of the electron-hopping process. The entropy change for the reaction PB ⇄ ES has proved to be dependent on the degree of crystallinity of the film, indicating that this entropy change is related to the fixation of inner counterions on the crystal structure of the films.
Surface modification of graphite+polymer composite and ITO electrodes by Nafion®+cupromeronic phthalocyanine films
Abstract The surface of indium tin oxide (ITO) and graphite+polymer composite electrodes can be modified by Nafion ® films containing a little amount of dispersed electroactive substances, such as phthalocyanines. This procedure allows the recovery of electroanalytical information on the electroactive deposited substance. The preparation methods for these types of modified electrodes are discussed from the voltammetric results obtained in this work. The Nafion ® net acts as a permeable membrane to the hydrogen ions. Furthermore, the presence of methylviologen within the Nafion ® film makes the electron transport throughout this membrane easy.
Correction of mass drift in ac-electrogravimetry of Prussian Yellow films. Mass impedance under apparently non-steady state condition
Abstract Mass impedance spectroscopy allows the modulated response of mass of a resonant electrode to be followed at different perturbation frequencies during electrochemical impedance spectroscopy experiments (ac-electrogravimetry). However, some difficulties appear if a continuous mass change takes place foreign to the mass changes due to the ac-modulated electrochemical processes. A new strategy is proposed to solve this limitation. Both, mass and potential analog signals are recorded frequency by frequency from 100 Hz up to the lowest frequencies. Then, a numerical procedure based on a multiparametric fitting of raw data against the elapsed time allows the contribution due to the modula…
Chloride role in the surface of nickel electrode
The chloride ion participation in the dissolution process on nickel electrodes in acid media as well as in the formation of the passive layer and in the pitting corrosion induction were studied. Composite electrodes containing nickel powder dispersed in a polymeric matrix show similar processes to those observed in polycrystalline nickel. Furthermore, phenformine hydrochloride inhibits the dissolution process due to the adsorption of the organic cation on the metal surface, although it does not protect the metal from pitting corrosion. Electrochemical impedance spectroscopy data allowed us to propose a physical model for the role of chloride ion in the dissolution and passivation processes …