Electrochemical impedance spectroscopy , description

In design of electrochemical sensors (and biosensors) especially helpful is electrochemical impedance spectroscopy (EIS), providing a complete description of an electrochemical system based on impedance measurements over a broad frequency range at various potentials, and determination of all the electrical characteristics of the interface.60-61 Generally it is based on application of electrical stimulus (known voltage or current) across a resistor through electrodes and observation of response... 

Conventional kinetics is largely concerned with the description of dynamic processes in the time domain, and in consequence few conceptual problems are encountered in understanding time resolved experiments. By contrast, frequency resolved measurements often pose more of a challenge to understanding, in spite of the obvious correspondence between the time and frequency domains. This conceptual difficulty may explain why the only frequency resolved method to achieve universal acceptance in electrochemistry is electrochemical impedance spectroscopy (EIS) [27-29], which analyses the response of electrochemical systems to periodic (sinusoidal) perturbations of voltage or current. It is clear that EIS is a very powerful method, and there... 

Usually, the starting point of model derivation is either a physical description along the channel or across the membrane electrode assembly (MEA). For HT-PEFCs, the interaction of product water and electrolyte deserves special attention. Water is produced on the cathode side of the fuel cell and will either be released to the gas phase or become adsorbed in the electrolyte. As can be derived from electrochemical impedance spectroscopy (EIS) measurements [14], water production and removal are not equally fast Water uptake of the membrane is very fast because the water production takes place inside the electrolyte, whereas the transport of water vapor to the gas channels is difiusion limited. It takes several minutes before a stationary state is reached for a single cell. The electrolyte, which consists of phosphoric add, water, and the membrane polymer, changes composition as a function of temperature and water content [15-18]. As a consequence, the proton conductivity changes as a function of current density [14, 19, 20). 

Direct current techniques assess the overall corrosion process occurring at a metal surface, but treat the metcd-solution interface as if it were a pure resistor. Electrochemical impedance spectroscopy (EIS) using small alternating currents has been developed in part to eliminate this restriction. For a full description of the EIS technique itself, the reader is referred to the literature [87] as well as to Chapter 7 of this manual. EIS has been particulariy useful in the presence of nonconducting and semiconducting surface films. 

The purpose of the present book is to satisfy this need. The book starts by covering the basic subjects of interfacial electrochemistry. This is followed by a description of some of the most important techniques (such as cyclic voltammetry, the rotating disc electrode, electrochemical impedance spectroscopy, and the electrochemical quartz-crystal microbalance). Finally, there is a rather detailed discussion of electroplating (including alloy deposition), corrosion, and electrochemical energy conversion devices (batteries, fuel cells and super-capacitors). 

Figure 69. Equivalent circuit for the description of generalized electrochemical processes in linear systems (see text).263 (Reprinted from J. Jamnik, Impedance spectroscopy of mixed conductors with semi-blocking boundaries Solid State Ionics, 157, 19-28. Copyright 2003 with permission from Elsevier.)...

There is a vast amount of literature on the subject of impedance measurements comprising a large number of different applications, such as corrosion, characterization of thin films and coatings, batteries, semiconductor electrodes, sensors, biological systems, and many more. It is beyond the scope of this article to cover all of these applications comprehensively. This chapter, therefore, concentrates on the description of the main principles and theories and selected applications of impedance methods. A more thorough treatment of the subject from the point of view of corrosion can be found in [1, 2], impedance spectroscopy of solid systems is described in [3]. The fundamentals of impedance spectroscopy of electrochemical systems are also explained in [4, 5]. 

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