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…

Validation of the mass response of a quartz crystal microbalance coated with Prussian Blue film for ac electrogravimetry

Prussian Blue (PB) films have been considerably studied for many research applications such as electrochromic material development, new material for batteries, etc. Many analytical techniques were employed for examining PB electrochemical behaviour in solution and the quartz crystal microbalance (QCM) used in the alternative regime (ac electrogravimetry) appeared as an attractive in situ mass sensor due to its low cost and its high mass sensitivity. Unfortunately, the validity of the common Sauerbrey equation was questionable with these films or in other terms if the QCM was used as a pure mass sensor. In this work PB film is examined through acoustic measurements and the response can be in…

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…

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…

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…

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

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…

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…

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 …

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…

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.

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…

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…

An electrochemical quartz crystal microbalance study of lithium insertion into thin films of tungsten trioxide I. Modeling of the ionic insertion mechanism

A theoretical description of the mechanism of lithium insertion into amorphous thin films of tungsten trioxide (a-WO3) prepared by thermal vacuum evaporation of WO3 powder is presented. The model developed is based on the experimental results obtained by chronoamperometry and ac impedance spectroscopy associated with electrochemical quartz crystal microbalance (EQCM). The electrode mass change and the current flowing through the electrochemical cell during cathodic polarization are simulta neously recorded. As expected, it can be observed that the insertion process is associated with a gain of mass of the inserted electrode at long times (t > 1 s). On the other hand at short times (t < 1 s)…

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 …

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…

A New Insight in the Electrochemical Response of a Depassivated Surface

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…

An electrochemical quartz crystal microbalance study of lithium insertion into thin films of tungsten trioxide II. Experimental results and comparison with model calculations

Abstract Lithium insertion into amorphous thin films of tungsten trioxide (a-WO 3 ) prepared by thermal vacuum evaporation of WO 3 powder has been studied experimentally by chronoamperometry, cyclic voltammetry and ac impedance spectroscopy associated with electrochemical quartz crystal microbalance (EQCM). During cathodic polarization of the electrode and at short times two antagonistic processes occur. One is a non faradaic process and is associated with the expulsion of anions from the electrode surface under the effect of the electric field built in the electrolyte when a potential difference is imposed between the electrodes. The other one is the faradaic insertion of non-solvated lith…

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…

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…

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.