0000000000328373
AUTHOR
J. Navarro-laboulais
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…
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 …
Experimental and CFD evaluation of ozone efficacy against coronavirus and enteric virus contamination on public transport surfaces
The limited information about the routes of the transmission of SARS-CoV-2 within the ongoing pandemic scenario mobilized the administration, industry and academy to develop sanitation and disinfection systems for public and private spaces. Ozone has been proposed as an effective disinfection method against enveloped and non-enveloped viruses, including viruses with similar morphology to SARS-CoV-2. Due to this efficacy, numerous gaseous and aqueous phase ozone applications have emerged potentially to inhibit virus persistence in aerosols, surfaces, and water. In this work, a numerical model, a RANS CFD model for ozone dispersion inside tram and underground coach has been developed includin…
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.
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.
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 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…
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.
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…
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.