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Unformatted text preview: Cyclic Voltammetry Cyclic Voltammetry Introduction Electrochemical analyses can be thought of in terms of two broad classes of measurement, one in which the potential that develops between two electrodes is measured (potentiometry) and another in which the current that flows between two electrodes is measured (amperometry). In potentiometry, it often proves helpful to arrange things such that the current is very low (e.g., by placing a highresistance voltmeter in series between two electrodes). The electrochemical potential of one electrode (the reference electrode) is usually fixed, so the measured cell potential can be interpreted in terms of an equilibrium halfcell reaction involving an analyte species in contact with the other electrode (the working electrode). In favorable cases, one can use data from potentiometric measurements to calculate analyte concentrations directly from the Nernst equation. Potentiometry is a simple and straightforward analytical method, and is routinely used to solve many problems in the analysis of electrochemically active and/or charged analytes. Figure 1. Schematic diagrams for twoelectrode electrochemical experiments. Left; Potentiometry. Right; Amperometry An important assumption in potentiometry is that the measured potential accurately reflects the equilibrium position of a welldefined electrochemical cell reaction. Often this is not the case, however, and potentiometric methods cannot be used. In many situations, it is instead more appropriate to control the potential of the working electrode (relative to a reference electrode) and to measure the resulting current. (Recall that current is simply the flow rate of electrons in a circuit; an ampere of current corresponds to a coulomb of charge flowing per second.) The magnitude of the resulting current and its dependence on the applied potential then provide the analytical information. An experiment in which the potential applied to the working electrode is swept at a constant sweep rate and the resulting current measured as a function of potential is called a voltammetry experiment, and much of the recent interest in electroanalytical chemistry stems from the use of voltammetry to obtain analytical (e.g., concentration), thermodynamic (e.g., redox potentials and equilibrium constants), kinetic (e.g., rate constants for reactions involving electrogenerated species) and mechanistic information about chemical systems in which redox chemistry plays a role. This laboratory experiment will introduce you to cyclic voltammetry as a simple, rapid, and powerful method for characterizing the electrochemical behavior of analytes that can be electrochemically oxidized or reduced. A number of excellent introductory articles on cyclic voltammetry have appeared, and you are encouraged to consult them for more information on the basics of voltammetry in general and on cyclic voltammetry in particular 13 . You will use solid electrodes made from two different materials, platinum and glassy carbon, in the course of this...
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This note was uploaded on 07/01/2011 for the course A 315 taught by Professor Arnold during the Fall '09 term at Indiana State University .
 Fall '09
 Arnold

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