Development of Simultaneous Measurement Method of Potentiodynamic Polarization Curve and Impedance Spectra Determined By Wavelet Transformation

Electrochemical impedance spectroscopy (EIS) is powerful method to analyze dissolution mechanisms of metals because time constants for elementary reaction steps and formation of reaction intermediate can be discriminated. Impedance spectrum is generally measured by using a frequency response analyzer (FRA) whose principle is on the basis of Fourier transformations of sinusoidal input and output signals. Ragoisha et al. (1) proposed a potentiodynamic electrochemical impedance spectroscopy (PDEIS), in which sinusoidal wavelet is superimposed on terrace of the each potential step during stepwise potential scan. Our group (2, 3) developed a simultaneous measurement method of a potential scanning impedance spectroscopy (PSIS) and impedance spectra determined by wavelet transformation (WT). In this method, it is possible to obtain the successive impedance spectra with measuring the potentiodynamic polarization curve of metal electrode simultaneously and to determine the instantaneous impedance. We used complex Morlet mother wavelet in order to obtain the complex number data in the frequency domain. This mother wavelet is obtained by combining the Gaussian function and sinusoidal term. The time-dependent impedance of the dissolving iron electrode can be determined by calculating cross spectra of the wavelet coefficients of current and potential signals. In the present paper, the potential step signal was used for the input signal. In the results, the impedance spectrum described the capacitive loop in the high frequency range and the inductive loop in the low frequency range, which was determined by WT. It was found that the impedance spectrum in the low frequency range determined by WT is related to the holding time of input potential signal. The inductive loop observed in the low frequency range and the holding time of input potential signal were discussed.

Reference:

1. G. A. Ragoisha and A. S. Bondarenko, Electrochimica Acta, 50, 1553 (2005).

2. M. Itagaki, K. Isobe, Y. Hoshi, I. Shitanda, 226^th ECS meeting abstract, #753 (2014).

3. M. Itagaki, A. Taya, K. Watanabe, Electrochemistry, 70, 779 (2002).