Electrochemical methods theory

Bard, A. J. Faulkner, L. R. Electrochemical Methods Theory and Applications John Wiley and Sons New York, 1980, p 143. 

Bard AJ, Faulkner LR (1980) Electrochemical Methods. John Wiley Sons, New York. Nicholson RS, Shain I (1964) Theory of Stationary Electrode Polarography. Anal Chem 36 706-723. 

An interesting attempt was made by Lehmann [16] to use an electrochemical method to speed up the separation of nitroglycerine. His theory was that gas evolved in the course of electrolysis would help nitroglycerine to rise to the surface. 

There is not space to detail all the theories, experiments and arguments which have been put forward. In earlier standards and draft revisions, variations on the original chemical method due to Crabtree and Kemp37 were used. In Britain and elsewhere, variations on the electrochemical method of Brewer and Milford38 became much more commonly used because they are continuous and may be automatic. More recently, the UV instrumental method which has the same advantages has become increasingly popular. 

The small area of a microelectrode, with its proportionately low capacitance, allows its use at very short time scales compared to the time scale used with a classical voltammetric electrode. As we have seen earlier in this chapter, when microelectrodes are used at short time scales, the current follows the behavior expected for diffusion in one dimension. Thus, the development of high-speed voltammetric methods with microelectrodes was a logical step, and has greatly expanded the scope and capabilities of electrochemical techniques [41]. Rapid electrochemical methods allow evaluation of the larger rate constants of rapid heterogeneous and/or homogeneous reactions. For example, theories of hetero-... 

It is the aim of this chapter to explain the basic requirements for performing electrochemistry, such as equipment, electrodes, electrochemical cells and boundary conditions to be respected. The following chapter focuses on the basic theory of charge transfer at the electrode-electrolyte solution interface and at transport phenomena of the analyte towards the electrode surface. In Chapter3, a theoretical overview of the electrochemical methods applied in the work described in this book is given. 

A large number of radical reactions proceed by redox mechanisms. These all require electron transfer (ET), often termed single electron transfer (SET), between two species and electrochemical methods are very useful to determine details of the reactions (see Chapter 6). We shall consider two examples here - reduction with samarium di-iodide (Sml2) and SRN1 (substitution, radical-nucleophilic, unimolecular) reactions. The SET steps can proceed by inner-sphere or outer-sphere mechanisms as defined in Marcus theory [19,20]. 

Refs. [i] Bard AJ, Faulkner LR (2001) Electrochemical methods. Wiley, New York [iiJRetter U, LohseH (2005) Electrochemical impedance spectroscopy. In Scholz F (ed) Electroanalytical methods. Springer, Berlin [in] Barsoukov E, Macdonald JR (ed) (2005) Impedance spectroscopy. Theory, experiment, and applications. Wiley, Hoboken... 

Refs. [i] Barna A, Porat DI (1989) Operational amplifiers. Wiley, New York [ii] Bard AJ Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, p 632 [Hi] Horowitz P, Hill W (1989) The art of electronics. Chap. 4, Cambridge University Press, Cambridge [iv] Clayton GB, Newby BWG (1992) Operational amplifiers. Buttersworth-Heinemann, Oxford [v] Clayton G, Winder S (2003) Operational amplifiers. Newness, Oxford [vi] Huijsing JH (2001) Operational amplifiers theory and design. Kluwer, Boston... 

In such a situation a catalytic current is measured. The crux of the electrochemical methods is to relate the ratio of kinetic, or catalytic, and diffusion currents to the rate coefficients of the respective rate-limiting chemical processes. In fact, the currents are comparatively easy to measure, and simple and cheap apparatus is available for doing this. The main disadvantage is that the theory is somewhat difficult to apply quantitatively. 

A. J. Bard and L. R. Faulkner, Electrochemical Methods Fundamentals and Applications, 2nd ed., Wiley, New York, 2001 Spectroelectrochemistry Theory and Practice, R. J. Gale, ed.. Plenum Press, New York, 1988 Electrochemical Interfaces Modern Techniques for In-Situ Interface Characterisation, H. D. Abruna, ed., VCH, New York, 1991 S. Pons, J. K. Foley, J. Russell and M. Seversen, Mod. Aspects Electrochem., 1986,17,223. 

The determination of the real surface area of the electrocatalysts is an important factor for the calculation of the important parameters in the electrochemical reactors. It has been noticed that the real surface area determined by the electrochemical methods depends on the method used and on the experimental conditions. The STM and similar techniques are quite expensive for this single purpose. It is possible to determine the real surface area by means of different electrochemical methods in the aqueous and non-aqueous solutions in the presence of a non-adsorbing electrolyte. The values of the roughness factor using the methods based on the Gouy-Chapman theory are dependent on the diffuse layer thickness via the electrolyte concentration or the solvent dielectric constant. In general, the methods for the determination of the real area are based on either the mass transfer processes under diffusion control, or the adsorption processes at the surface or the measurements of the differential capacitance in the double layer region [56],... 

Electrochemical methods have an enormous potential for characterization and studying thin films on the metal surfaces. An excellent recent review describes in great detail the theory and applications of these methods to gold-thiol monolayers13. In this section we briefly discuss the main phenomena which can be addressed by electrochemical methods and describe the most popular surface-immobilized electroactive functional groups used for this purpose. 

Fletcher S 1993 Contribution to the theory of conducting-polymer electrode in electrolyte solutions J. Chem. Soc. Faraday Trans. 89 311-20 Kanatzidis M G 1990 Conductive Polymers Chem. Eng. News 68(49) 36-54 Bard A J and Faulkner L R 1980 Electrochemical Methods Fundamentals and Applications (New York Wiley)... 

There are probably several reasons why electrochemical methods are not as popular as chromatographic or optical methods. One is that electrochemistry and electrochemical methods are not emphasized in typical college curricula. One can cite the nearly universal disappearance of fundamental electrochemistry from beginning general and physical-chemistry courses, whereas the interaction of electromagnetic radiation with matter and the energy levels concerned is covered in many first-year courses. Electrochemical theory is really no more complex or abstruse, but probably not so well unified at present, as spectrochemical theory. 

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