Impedance Spectroscopy

Preface

Since its conceptual introduction in the late 19th century, the impedance spectroscopy has undergone a tremendous evolution into a rich and vibrant multidisciplinary science. Over the last decade Electrochemical Impedance Spectroscopy (EIS) has become established as one of the most popular analytical tools in materials research. The technique is being widely and effectively applied to a large number of important areas of materials research and analysis, such as corrosion studies and corrosion control; monitoring of properties of electronic and ionic conducting polymers, colloids and coatings; measurements in energy storage, batteries, and fuel cells-related systems; biological analysis and biomedical sensors; measurements in semiconductors and solid electrolytes; studies of electrochemical kinetics, reactions and processes. Impedance spectroscopy is a powerful technique for investigating electrochemical systems and processes. EIS allows to study, among others, such processes as adsorption, charge- and mass-transport, and kinetics of coupled sequential and parallel reactions.

In a broader sense, EIS is an extraordinarily versatile, sensitive, and informative technique broadly applicable to studies of electrochemical kinetics at electrode-media interfaces and determination of conduction mechanisms in various materials through bound or mobile electronic, ionic, semiconductor, and mixed charges. Impedance analysis is fundamentally based on a relatively simple electrical measurement that can be automated and remotely controlled. Its main strength lies in its ability to interrogate relaxation phenomena whose time constants ranging over several orders of magnitude from minutes down to microseconds. In contrast to other analytical techniques, EIS is noninvasive technique that can be used for on-line analysis and diagnostics. The method offers the most powerful on-line and off-line analysis of the status of electrodes, monitors and probes in many different complex time- and space-resolved processes that occur during electrochemical experiments. For instance, the EIS technique has been broadly practiced in the development of sensors for monitoring rates of materials' degradation, such as metal corrosion and biofouling of implantable medical devices.

EIS is useful as an empirical quality-control procedure that can also be employed to interpret fundamental electrochemical and electronic processes. Experimental impedance results can be correlated with many practically useful chemical, physical, mechanical, and electrical variables. With the current availability of ever evolving automated impedance equipment covering broad frequency and potential ranges, the EIS studies have become increasingly popular as more and more electrochemists, material scientists, and engineers understand the theoretical basis for impedance spectroscopy and gain skill in the impedance data interpretation.

The impedance technique appears destined to play an increasingly important role in fundamental and applied electrochemistry and material science in the coming years. However, broader practical utilization of EIS has been hindered by the lack of comprehensive and cohesive explanation of the theory, measurements, analysis techniques, and types of acquired data for different investigated systems. These factors may be connected with the fact that existing literature reviews of EIS are very often difficult to understand by non-specialists. As will be shown later, the ambiguity of impedance data interpretation and the establishment of direct relationships with practical physical, chemical, electrical, and mechanical parameters constitute the main disadvantages of the technique. These general weaknesses are amplified especially when considering a great variety of practical impedance applications, where a practical investigator or researcher often has to decide if any of the previously known impedance response models and their interpretations are even remotely applicable to the problem in hand. EIS data demonstrate the investigated system's response to applied alternating or direct electrical fields. It becomes the investigators' responsibility to convert the electrical data into parameters of interest, whether it is a concentration of bioanalyte, corrosion rate of metal surfaces, performance characteristics of various components of a fuel cell, or rate of oxidative decomposition of polymer films.

As industrial scientist and engineer with career encompassing multiple senior technology and product development positions in leading R&D divisions in Specialty Chemicals, Electronics, BioMedical, and Aerospace industrial corporations, the author has learned over the years to greatly appreciate the investigative power and flexibility of EIS and impedance-based devices in commercial product development. This book was born out of acute need to catalog and explain multiple variations of the EIS data characteristics encountered in many different practical applications. Although the principle behind the method remains the same, the impedance phenomena investigation in different systems presents a widely different data pattern and requires significant variability in the experimental methodology and interpretation strategy to make sense of the results. The EIS experimental data interpretation for both unknown experimental systems, and well-known systems investigated by other (non-electrochemical) means is widely acknowledged to be the main source of the method's application challenge, often listed at the main impediment to the method's broader penetration into scientific and technological markets. This book attempts to at least partially standardize the catalog of EIS responses across many practically encountered fields of use and to present a coherent approach to the analysis of experimental results.

This book is intended to serve as a reference on the topic of practical applications of impedance spectroscopy, while also addressing some of the most basic aspects of EIS theory. The theory of the impedance spectroscopy has been presented in great details and with remarkable skill in well-received monographs by J. R. MacDonald, and recently by M. Orazem and B. Tribollet, as well as in many excellent review chapters referenced in this book. There are a number of short courses, several monographs and many independent publications on the impedance spectroscopy. However, the formal courses on the topic are rarely offered in the university settings. At the same time, there is a significant worldwide need to offer independent, direct and comprehensive training on practical applications of the impedance analysis to many industrial scientists and engineers relatively unfamiliar with the EIS theory but eager to apply impedance analysis to address their everyday product development technological challenges. This manuscript emphasizes practical applications of the impedance spectroscopy. This book in based around a catalogue representing a typical impedance data for large variety of established, emerging, and non-conventional experimental systems; relevant mathematical expressions; and physical and chemical interpretation of the experimental results. Many of these events are encountered in the field by industrial scientists and engineers in electrochemistry, physical and analytical chemistry, and chemical engineering.

This book attempts to present a balance of theoretical considerations and practical applications for problem solving in several of the most widely used fields where electrochemical impedance spectroscopy analysis is being employed. The goal was to produce a text that would be useful to both the novice and the expert in EIS. It is primarily intended for industrial researchers (material scientists, analytical and physical chemists, chemical engineers, material researchers), and applications scientists, wishing to understand how to correctly make impedance measurements, interpret the results, compare results with expected previously published results form similar chemical systems, and use correct mathematical formulas to verify the accuracy of the data. A majority of these individuals reside in the specialty chemicals, polymers, colloids, electrochemical renewable energy and power sources, material science, electronics, biomedical, pharmaceutical, personal care and other smaller industries. The book intends to provide a working background for the practical scientist or engineer who wishes to apply EIS as a method of analysis without needing to become an expert electrochemist. With that in mind, both somewhat oversimplified electrochemical models and in-depth analysis of specific topics of common interest are presented. The manuscript covers many of the topics needed to help readers identify whether EIS may be an appropriate method for their particular practical application or research problem. A number of practical examples and graphical representations of the typical data in the most common practical experimental systems are presented. In that respect the book may also be addressed to students and researchers who may found the presented catalog of impedance phenomenological data and the relevant discussions to be of assistance in their introduction to theoretical and practical aspects of electrochemical research.

Starting with general principles, the book emphasizes practical applications of the electrochemical impedance spectroscopy to separate studies of bulk solution and interfacial processes, using of different electrochemical cells and equipment for experimental characterization of different systems. The monograph provides relevant examples of characterization of large variety of materials in electrochemistry, such as polymers, colloids, coatings, biomedical species, metal oxides, corroded metals, solid-state devices, and electrochemical...