Identification of electroactive sites in Prussian Yellow films

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 electrochemical processes for the interpretation of the whole electrochemical response. One of these processes corresponds to the oxidation of View the MathML source units where the electrical charge is balanced by the exchange of neighbor potassium cations. The second one is associated to the oxidation of View the MathML source trapped sites and the third one also to the oxidation of View the MathML source units but in this last case, the absence of neighbor potassium cations causes that the electrical charge balance takes place by the exchange of some anions such as the chloride. These processes have been identified on the basis of previous results and on the interesting information provided by the coupling voltammetry and absorbance derivative curves at these characteristic wavelengths

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

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)

International audienceA new transfer model is proposed to explain ac-electrogravimetry response of p-dopedfilms. This modeltakes into account the exclusion effect occurring as a result of the anion transfer. The insertion/expulsionof anions inside afilm involves simultaneously the expulsion/insertion of free solvent molecules. Thenumber of solvent molecules excluded depends on the volume of anion transferred. Solvent transferstimulated by the conformational changes offilms constitutes the remaining electrogravimetric responsewhen the exclusion process cannot explain by itself this response. Consequently, the kinetics of this freesolvent transfer can be directly related to the kinetics of conformational changes. This model wasvalidated in poly(o-toluidine) thinfilms where electrochemical kinetics were quantitatively investigatedas a function of the applied potential. As far as we know, for thefirst time, charge transfer andconformational changes could be kinetically separated. This new transfer model may respond tofundamental questions on the electrochemistry of conducting polymers, which may have a significantimpact on a large number of applications

Electrochromic behavior of Prussian Yellow

Prussian Blue films were studied by in situ electrogravimetric and spectroelectrochemical methods during the electrochemical oxidation to the Prussian Yellow form. Spectroelectrochemical studies detected important absorbance changes during electrochemical experiments at 430 nm and 690 nm corresponding to the appearance of the yellow form and to the disappearance of the characteristic blue color. These changes of absorbance were well related with the voltammetric peaks. This redox process has also been studied by in situ electrochemical impedance spectroscopy, mass impedance and color impedance at 690 nm. It has been found that crossed impedance functions obtained from the original ones provide interesting information on the participation of both, cations and anions during electrochemical processes