14.1.2 The three-electrode configuration
A three-electrode configuration is used in the FlexCell (
Figure 14–2: Schematic representation of
an electrochemical cell with a three-electrode configuration (Page 103)
). The working potential is
set between the working electrode (WE) and the auxiliary electrode (AUX). The auxiliary
electrode is kept at the same precisely defined potential as the reference electrode (REF) by
means of a “voltage clamp”, an electronic feedback circuit that compensates for polarization
effects at the electrodes. At the working electrode, which is kept at virtual ground, the
electrochemical reaction takes place (that is, electrons are transferred at the working electrode).
This results in an electrical current to the I/E converter, which is a special type of operational
amplifier. The output voltage can be processed by an integrator, recorder, or AD convertor to
generate the chromatogram.
Figure 14–2: Schematic representation of an electrochemical cell with a three-electrode
configuration
Essentially, for the oxidation or reduction reaction it would be sufficient to use only two
electrodes. However, the three-electrode configuration has several advantages over a two-
electrode configuration:
• If the working potential were applied only over an auxiliary electrode versus the working
electrode (without reference electrode), the working potential would continuously change due
to polarization effects at the electrodes, resulting in highly unstable working conditions.
• If the working potential were applied only over the reference electrode versus the working
electrode (without auxiliary electrode), the working potential would be very well defined.
However, the potential of a reference electrode is only well defined if the current drawn is
extremely low (pico-amperes), resulting in a very limited dynamic range.
A three-electrode configuration combines the best of both configurations. The reference electrode
stabilizes the working potential and the auxiliary electrode can supply high currents. This results
in the tremendous dynamic range of a three-electrode system.
December 16, 2021, 715007395 Ver. 00
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