Impedance techniques electrochemical

D.C. Silverman, Primer on AC Impedance Technique, Electrochemical Techniques for Corrosion Engineering, R. Baboian, Ed., NACE International, 1986, p 73-79... 

The apphcation of an impressed alternating current on a metal specimen can generate information on the state of the surface of the specimen. The corrosion behavior of the surface of an electrode is related to the way in which that surface responds to this electrochemical circmt. The AC impedance technique involves the application of a small sinusoidal voltage across this circuit. The frequency of that alternating signal is varied. The voltage and current response of the system are measured. 

Electrochemical tests This group includes the various electrochemical tests that have been proposed and used over the last fifty or so years. These tests include a number of techniques ranging from the measurement of potential-time curves, electrical resistance and capacitance to the more complex a.c. impedance methods. The various methods have been reviewed by Walter . As the complexity of the technique increases, i.e. in the above order, the data that are produced will provide more types of information for the metal-paint system. Thus, the impedance techniques can provide information on the water uptake, barrier action, damaged area and delamination of the coating as well as the corrosion rate and corroded area of the metal. However, it must be emphasised that the more comprehensive the technique the greater the difficulties that will arise in interpretation and in reproducibility. In fact, there is a school of thought that holds that d.c. methods are as reliable as a.c. methods. 

Developments in electrochemical methods since 1976 for measurement of corrosion have been rapid. Research and development has produced several new techniques, e.g. a.c. impedance and electrochemical noise. These methods require corrosion expertise for both operation and interpretation. Industry generally prefers instrumentation that can be operated by process... 

The use of a heavy arsenal of surface science (XPS, UPS, STM, AES, TPD) and electrochemical (cyclic voltammetry, AC Impedance) techniques (Chapter 5) showed that Equations (12.2) and (12.3) simply reflect the formation of an overall neutral backspillover formed double layer at the metal/gas interface. It thus became obvious that electrochemical promotion is just catalysis in presence of a controllable double layer which affects the bonding strength, Eb, of reactants and intermediates frequently in the simple form ... 

Deslouis C, Maurin G, Pebere N, Tribollet B (1988) Investigation of tellurium electrocrystal-Uzation by EHD impedance technique. J Appl Electrochem 18 745-750 Yagi I, Nakabayashi S, Uosaki K (1998) In situ optical second harmonic rotational anisotropy measurements of an Au(l 11) electrode during electrochemical deposition of tellurium. J Phys Chem B 102 2677-2683... 

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

Among a few electrochemical techniques available for studying the adsorption, the AC impedance technique has been most widely employed. Its high sensitivity to the physico-... 

One of the most powerful methods for the investigation of electrochemical reactions is the use of alternating current (AC) impedance techniques. In order to understand the basis of this approach, however, it is helpful first to consider some simple electronic analogues which mimic closely the systems of electrochemical interest. 

Only a small selection of the variants in the electrochemical literature can be mentioned here. Thus, impedance techniques (small amplitude sinusoidal perturbation at the electrode with observation of the system s response [22]) as well as polaro-graphic methods (at mercury electrodes) will not be described. Since the notion of a reaction mechanism requires consumption of substance, equilibrium techniques (such as potentiometry) will also not be discussed here. 

For an excellent introductory reading on ac impedance techniques for the purpose of ion conductivity measurement or study of interfacial properties, please see Linford, R. G. In Electrochemical Science and Technology of Polymers, 2nd ed. Linford, R. G., Ed. Elsevier Applied Science London, 1990 p 281. 

However, as mentioned in section 6, our awareness of this situation is not the same as being able to quantify the contributions of these various physical processes to the performance of a particular electrode under a specific set of conditions or in understanding all the factors that govern the rates of these processes. Unfortunately, due to the inherently convoluted nature of electrochemical and chemical processes, it has proven extremely difficult to isolate and study these processes individually in a complex system. We saw in sections 3—5 that impedance techniques can in some cases be used to isolate the linearized resistance of the interface from that of slower chemical steps via time scale. Various workers... 

Electrochemical Characterization Technloues. Since corrosion Is an electrochemical process, It Is not surprising that a considerable amount of work has been reported over the years on electrical and electrochemical techniques for the study of the corrosion process. Leldhelser Ql.) and Szauer (12.> 11) have provided good reviews of the principal techniques. Walter has recently provided a review of DC electrochemical tests for painted metals (14). Both AC and DC methods have been employed to study a variety of Issues related to corrosion and corrosion protection. DC techniques are especially useful for studying substrate processes, while AC impedance techniques are most useful for studying processes relating to coated substrates and the performance of coatings. 

The electrochemical response to an a.c. perturbation is very important in impedance techniques (Chapter 11). This response cannot be understood without a knowledge of the fundamental principles of a.c. circuits1, which is presented in this appendix. 

The methods of measuring corrosion rates in the course of testing corrosion inhibitors are conventional weight loss, electrochemical techniques such as linear polarization resistance, potentiodynamic polarization, AC impedance, and electrochemical potential or current noise. 

Gabrielli C, Keddam M, Takenouti LI (1990) New trends in the investigation of electrochemical systems by impedance techniques multi-transfer function analysis. Electrochim Acta 35 1553-7... 

The a.c. impedance technique [33,34] is used to study the response of the specimen electrode to perturbations in potential. Electrochemical processes occur at finite rates and may thus be out of phase with the oscillating voltage. The frequency response of the electrode may then be represented by an equivalent electrical circuit consisting of capacitances, resistances, and inductors arranged in series and parallel. A simplified circuit is shown in Fig. 16 together with a Nyquist plot which expresses the impedance of the system as a vector quantity. The pattern of such plots indicates the type and magnitude of the components in the equivalent electrical network [35]. 

Gabrielli, C. Use and Applications of Electrochemical Impedance Techniques. Solartron Instruments, Schlumberger Technologies, England, Technical Report 12860013, 1990. 

In another study also, electrochemical impedance technique has been shown to be a useful method for a DNA biosensor using a multinuclear nickel(II) salicylaldimine metallodendrimer platform [164], Both the preparation of the dendrimer-modified GCE surface and the immobilization of DNA have been effectively done by simple drop-coating procedures. The metallodendrimer is electroactive exhibiting two redox couples in phosphate buffer solution. The impedance study demonstrated that the DNA biosensor responded well to 5 nM of target DNA by displaying a decrease in charge transfer resistance in phosphate buffer solution and increase in charge transfer resistance in the presence of the [Fe(CN)6]3/4" redox probe. 

Electrochemical methods can also be used for obtaining analytical information on porous materials. Voltammetric methods and related techniques have been largely used to acquire information on reaction mechanisms for species in solution phase, whereas impedance techniques have been extensively used in corrosion and metal surface studies. In the past decades, the scope of available methods has been increased by the development of the voltammetry of microparticles (Scholz et al., 1989a,b). This methodology, conceived as the recording of the voltammetric response of a solid material mechanically transferred to the surface of an inert electrode, provides information on the chemical composition, mineralogical composition, and speciation of solids (Scholz and Lange, 1992 Scholz and Meyer, 1994, 1998 ... 

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