Dynamic electrochemical impedance spectroscopy of the adsorption and relaxation of polyaniline chains during potentiodynamic redox transformations

A new approach to an equivalent circuit analysis of impedance spectra of a conducting polyaniline (PAni) layer is presented. Film properties are often modeled by constant-phase elements (CPE), which are closer to experimental results than capacitors. We want to take an insight into the CPE. We propose a novel equivalent circuit based on the Frumkin-Melik-Gaikazyan adsorption model, as we suppose that the PAni layer molecules may behave like other adsorbing and relaxing organic compounds. Measurements are performed using recently developed experimental technique—dynamic electrochemical impedance spectroscopy. Obtained spectra are analyzed using the proposed equivalent circuits. Characteristics of several parameters are analyzed and discussed. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 9, pp. 1111–1119. The text was submitted by the authors in English.     

Identification and localization of organic coating degradation onset by impedance imaging

The aim of this work was to demonstrate the potential of a localized impedance measurement technique to identify and spatially localize the onset spots of polymeric coating degradation. The technique, which has not yet been applied in the field of organic coatings, utilizes atomic force microscopy (AFM) in contact mode. During the scan a single-frequency voltage perturbation signal is applied between the AFM tip and the coated metal substrate. A current response signal is registered. As a result an impedance map of the scanned region is created. The method was applied to investigation of acrylic coating degradation during exposure to UV radiation. Localized topography and impedance images revealed formation of micro-cracks in the coating layer, which gradually converted into through-the-coating defects with an increase in the irradiation time. Thus the method allowed early identification and localization of the sites of degradation onset, which was not possible using classical impedance measurement.     

On the joint time-frequency characteristics of chemical oscillations

A method of time-frequency transformations of nonstationary signals has been discussed and applied to the analysis of oscillatory Belousov-Zhabotinsky (BZ) reaction. Selected registers of BZ reactions, that represent regular and complex dynamic behavior, have been submitted to the detailed spectral analysis using the short time Fourier transform (STFT). It has been demonstrated that the STFT is an accurate and suitable method for decomposition of chemical oscillations in the joint time and frequency domain. The energy distribution via STFT, presented in this article, revealed some specific characteristics of transitions between different regimes in the closed system of BZ reaction.     

Analysis of Spontaneous Electrochemical Oscillations by the Wavelet Transformation Method

A new way of analyzing current oscillations that accompany anodic metal dissolution is presented. A wavelet transformation is used for separation and spectral analysis of singular courses—elementary components of electrochemical oscillation recordings. A method of obtaining oscillation energy distribution analogous to the spectral power density function is presented. It is shown that the chaotic component (Shil'nikov chaos) can be separated from the deterministic component of the described process.     

Digital Harmonic Analysis of Cadmium Ion Reduction on a Dropping Mercury Electrode

The cadmium ions reduction on a mercury electrode is investigated. A sinusoidal voltage perturbation signal, superimposed on a linearly changing dc potential, is used. A total time–frequency analysis of the polarographic current of cadmium ions reduction on a dropping mercury electrode is performed. Classical Fourier transform leads to decomposition of the polarographic current into its harmonics. The current harmonics determined by Fourier transform are potential-independent. The STFT transform of the polarographic current also leads to its decomposition into harmonics. However, application of the STFT transform correctly reflects changes in the current harmonics as the function of potential.     

Analysis of electrochemical noise by means of bispectral technique

Nonlinear processes are often encountered in the practice of electrochemical and corrosion measurements. Especially, activation-controlled processes are inherently nonlinear. Taking into account investigations of electrode reactions, linear approximation is a popular approach. In this introductory paper, the possibility of extension of electrochemical noise (EN) measurements to the nonlinear regime is presented. Natural consequence of focusing on nonlinear processes is application of higher-order spectral techniques. Utilization of bispectral representation enables analysis of stationarity and linearity properties of EN. The authors present algorithm enabling assessment of both quantities and also exemplary analysis of noise generated during cathodic polarization, which is important for corrosion protection. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16 March 2005. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Ellipsometric study of oxide formation on Cu electrode in 0.1 M NaOH

A single wavelength ellipsometry and cyclic voltammetry measurements were simultaneously used for the investigation of oxide growth on copper in 0.1 M NaOH solution. These investigations were part of joint research of electric and physical properties of cuprous and cupric oxide during layer formation and growth. This type of joint impedance and ellipsometric study has not been performed before. In this paper, authors discuss composition of multilayer film structure using various models and fitting methods enabling interpretation of multilayer oxides structure formation during passivation process. It is shown that implementation of effective medium approximation allows to obtain an accurate model fitting, using Levenberg–Marquardt optimization algorithm and mean square error.     

A Novel Method of Spectral Analysis of Oscillatory Belousov–Zhabotinsky Reaction

This paper is a preliminary study of time–frequency behavior of homogenous Belousov–Zhabotinsky reaction in a batch reactor. A series of measurements performed for a variable concentration of the reaction substrates led to the conclusion that there exists time-dependency of an instantaneous frequency of fundamental frequency and harmonics and of electrode potential fluctuations generated during the process discussed. The Short Time Fourier Transformation (STFT) was proposed for analyzing electrode potential registers. On the basis of STFT analysis a decrease in frequency of oscillations of exponential character has been postulated.