J.J. García-Jareño

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 microbalance in solutions without monomer allows to discern between the role of different charged species which are present in the solution: salt cations (Cs+, Na+ and K+), salt anions (NO3−, Cl−, I− and Br−) and hydrated protons that can compensate electrical charge within the film during electrochemical processes.

Impedance analysis of Prussian Blue films deposited on ITO electrodes

Abstract A study of the electrochemical impedance spectroscopy (EIS) of Prussian Blue (PB) films deposited on Indium Tin Oxide (ITO) electrodes in a 1 M KCl solution has been carried out in this work. The charge transport process across the film is modeled with an equivalent circuit considering two phases and two kinds of charge transport in Prussian Blue films. The dependence of diffusion coefficients and other circuit parameters with film thickness and the redoxstate of the film has been studied. Diffusion coefficients reach a maximum value near the equilibrium potential and the charge transport resistance at the ITO/PB interface has a minimum value at these potentials. p]The total capacitance has a linear dependency with film thickness and could be used to measure the amount of Prussian Blue deposited.

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 the low electronic conductivity of the material. In spite of this, the thin films deposited on the ITO electrode can act as a pH potentiometric sensor.

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 of nickel electrodes.

An electrochemical impedance and ac-electrogravimetry study of PNR films in aqueous salt media

Abstract 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.

Charge compensation process in polypyrrole studied by ac electrogravimetry

Abstract Ions and solvent insertion/expulsion during the redox reaction of polypyrrole were investigated. Simultaneous measurement of impedance and mass/potential transfer function, thanks to a fast quartz crystal microbalance, allows species movement to be determined. For polypyrrole in CsCl, Na 2 SO 4 and NaCl, cations and solvent were expelled and anions inserted when the film was oxidised. The insertion isotherm was obtained and it was shown that bigger ions are hosted in the polymer at cathodic potential.

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 interpreted as a pure mass change if the thickness is around 0.15 μm. Over this limit, film viscoelastic contributions can affect drastically the mass change estimation: if the thickness is two times larger, the mass error reaches 40%.

Electrochemical study of Nafion membranes/Prussian blue films on ITO electrodes

Nafion (perfluorinated ion-exchange membrane) films allow the transport of counterions from the solution to the PB film necessary during the reduction and oxidation processes to maintain the film electroneutrality. Nafion films cause a decrease in the apparent diffusion coefficient. This apparent diffusion coefficient could be interpreted as a measurement of counterions transport through films. Prussian blue films stability is increased by the presence of Nafion films allowing the study of the electrochemical behaviour of the oxidized form of Prussian blue films (Berlin green, Prussian yellow) by impedance spectroscopy.

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.

Charge transport in prussian blue films deposited on ito electrodes

Abstract Charge transport processes that can occur in Prussian Blue films deposited on ITO (indiumtin oxide) electrodes in contact with aqueous solutions have been studied. The concentration in the solution of some ions such as the proton or the potassium influence the films conductivity as well as the degree of hydration of the film. This points to the fact that Prussian Blue films act as ionic conductors when they are immersed in aqueous solutions. Furthermore, the apparent diffusion coefficient calculated from impedance spectra of PB films increases with the temperature which confirms the idea of an ionic conductor. The impedance spectra for the Everitts Salt films, however, differ from the PB films and is much less sensitive to temperature.