Page 115 - Analytical Electrochemistry 2d Ed - Jospeh Wang

Analytical Electrochemistry, Second Edition. Joseph Wang
Copyright # 2000 Wiley-VCH
ISBNs: 0-471-28272-3 (Hardback); 0-471-22823-0 (Electronic)

CHAPTER 4

PRACTICAL CONSIDERATIONS

The basic instrumentation required for controlled-potential experiments is rela-
tively inexpensive and readily available commercially. The basic necessities include
a cell (with a three-electrode system), a voltammetric analyzer (consisting of a
potentiostatic circuitry and a voltage ramp generator), and an X±Y±t recorder (or
plotter). Modern voltammetric analyzers are versatile enough to perform many
modes of operation. Depending upon the speci®c experiment, other components may
be required. For example, a faradaic cage is desired for work with ultramicroelec-
trodes. The system should be located in a room free from major electrical
interferences, vibrations, and drastic ¯uctuations in temperature.

4-1 ELECTROCHEMICAL CELLS

Three-electrode cells (e.g., Figure 4-1) are commonly used in controlled-potential
experiments. The cell is usually a covered beaker of 5±50 mL volume, and contains
the three electrodes (working, reference, and auxiliary), which are immersed in the
sample solution. While the working electrode is the electrode at which the reaction
of interest occurs, the reference electrode provides a stable and reproducible
potential (independent of the sample composition), against which the potential of
the working electrode is compared. Such ``buffering'' against potential changes is
achieved by a constant composition of both forms of its redox couple, for example,
Ag=AgCl or Hg=Hg 2 Cl 2 , as with the commonly used silver±silver chloride and the
saturated calomel reference electrodes, respectively. To minimize contamination of
the sample solution, the reference electrode may be insulated from the sample

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