Impedance Measurement Techniques

The application of a sine wave excitation to a system under test often is the easiest method of determining the system transfer function. Here we are concerned with measuring or inferring a transfer function for an electrochemical ceU as a first 

Impedance Spectroscopy, Second Edition, edited by Evgenij Barsoukov and J. Ross Macdonald ISBN 0-471-64749-7 Copyright 2005 by John Wiley Sons, Inc. 

Step in determining reaction mechanistic and kinetic parameters (Macdonald [1977], Gabrielli [1981], Macdonald andMcKubre [1981], Macdonald and McKubre [1982]). 

By way of review, the transfer function of a system can be determined as the output divided by the input 

For the special case where the output signal is the system voltage and the input (or excitation function) is the current, the transfer function is the system impedance 

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Conductivity measurements are commonly performed on membranes using AC impedance measurement techniques [34]. In such experiments, the membrane is generally considered to be uniformly equilibrated with water vapour and thus that the gradient in water content is zero. It follows from Eq. (4.22) that the protonic flux is then proportional to the potential gradient in the membrane as... 

Impedance Measurement Techniques 157 Table 3.1.1. Property of Common Analog-to-Digital Converters... 

Froguet, M., and Pagetti, J. (1989). Contribution of the electrochemical impedence measurement technique in zinc corrosion inhibition studies in acid media. Werksi. Korros., 40, 634-641 (in English). 

Nickel-base alloys respond well to most electrochemical test techniques and show active-passive behavior in many environments. Due to their rapid repassivation, however, the results obtained with potentiod3mamic techniques can sometimes be affected by scan rate and immersion time prior to starting the test [5,6], Electrochemical techniques are useful for investigating localized corrosion resistance, ASTM G 61, Test Method for Conducting Cyclic Potentio-dynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys, and general corrosion resistance, ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements of nickel alloys. Electrochemical impedance measurement techniques have not been extensively applied to nickel alloys. 

In the present state-of-the-art equipment, it is possible to measure and plot the electrochemical impedance automatically. Electronic circuitry is designed to generate the frequency sweep of a desired resolution over the range of interest. The generator can be programmed to sweep from a maximum to a minimum frequency in a number of required frequency steps. The commonly used modem equipment AC impedance measurement techniques can be subdivided into two main groups - single sine (lock-in amplification and frequency response analysis) and multiple sine techniques such as fast Fourier transforms (FFT). 

Yoo J-S, Park S-M (2000) An electrochemical impedance measurement technique employing Foiffier transform. Anal Chem 72 2035-2041... 

J. -S. Yoo, S.-M. Park, An electrochemical impedance measurement technique employing Fourier transform. Anal. Chem., 2000,72, pp. 2035-2041. 

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