Connection of CVs and impedance spectra of reversible redox systems, as used for the validation of a dynamic electrochem
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ORIGINAL PAPER
Connection of CVs and impedance spectra of reversible redox systems, as used for the validation of a dynamic electrochemical impedance spectrum measurement system Tamás Pajkossy 1
&
Gábor Mészáros 1
Received: 5 May 2020 / Revised: 20 May 2020 / Accepted: 20 May 2020 # The Author(s) 2020
Abstract With the purpose of fast characterization of electrode reactions, a dynamic electrochemical impedance spectrum (dEIS) measurement system has been assembled which permits the continuous collection of audio-frequency impedance spectra while performing cyclic voltammetry measurements with the usual scan rates of up to 200 mV/s. The performance of this system was tested by analyzing the CV curves and impedance spectra taken simultaneously in ferro-/ferricyanide containing aqueous solutions yielding an experimental demonstration of the connection of the semi-integrated reversible voltammograms and the Warburg coefficients. Keywords Impedance . Interface . Diffusion . Semi-integration . Voltammetry
Introduction Electrochemical impedance spectroscopy (EIS) is a widely used method of electrochemists; its main role is the determination of rates of interfacial processes. Impedance measurements are usually performed by applying a sinusoidal perturbation of ω frequency upon the potential or current and correlating the ac terms of these two quantities to each other. The Z(ω) impedance spectra are compiled from frequency-byfrequency measurements. Devices needed for this method are commercially available and precise, though the measurement itself can be somewhat time-consuming, especially at low frequencies. There are a couple of conditions which must prevail for the EIS measurement. The system should be in steady state for the time of the measurement even at the lowermost frequency. This is generally achieved at the “static” EIS measurements, This paper is dedicated to Fritz Scholz on the occasion of his 65th birthday, to express our high respect towards his contribution to electrochemistry and dissemination of its concepts. * Tamás Pajkossy [email protected] 1
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2, Budapest H-1117, Hungary
i.e., when the ac perturbation of potential (or current) is applied upon a constant dc potential (or current). Nevertheless, if some properties of the system are slowly changing, then the lowermost frequency should be chosen accordingly. In the same vein, the time of taking the complete spectrum should be minimized. A possible way of making the measurement faster is to use periodic perturbation with a periodic function comprising many harmonics. The signals of the perturbed potential and that of the corresponding current response are Fourier-transformed, and impedance values are calculated for each harmonic component. Since the overall potential perturbation must not exceed a few millivolts to keep the currentvoltage relation in a linear range, the phases of the harmonics must be carefully chosen. A random selection
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