A. Sanmatı́as

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.

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 channels of Prussian Blue.

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.

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 ⇄ Everitts 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.

Temperature dependence of impedance spectra of Prussian Blue films deposited on ITO electrodes

The dependence of the charge-transport rates on the redox state of the PB film has been studied. The temperature dependence of the impedance spectra of Prussian Blue films has been studied at several stabilization potentials between the totally reduced form, Everitts Salt, and the mixed-valence form, Prussian Blue. An increase in the apparent diffusion coefficient is obtained for films in the blue form, while at intermediate potentials, when the faradaic processes are taking place, the film resistance, evaluated from the impedance spectra, does not vary in an important way. However, at these potentials, a more amorphous film shows a clear increase in the resistance of the film with the temperature. This increase is explained considering an electron-hopping conduction through the film which needs the fixing of positive ions (perhaps hydrogen ions) on the appropriate centres to allow the electron transfer between neighbouring iron sites.

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 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.

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 throughout this membrane easy.

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.

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.