70
eDAQ Potentiostats
With highly resistive loads, using a large range setting with a small
(close to zero) current can produce unexpected large potential signals
because of small offsets in the current control circuitry. If you require
very small currents always use a small range setting as well, this will
ensure a minimum offset error. For example, to apply a current of only
25 nA use the 100 nA range setting for best results.
Controlled Potential Electrolysis
This technique is essentially the same as
, and is also known as amperometry. A constant
potential is applied at the working electrode which is sufficient to
oxidize or reduce the substrate. As the electrolysis continues the
substrate is eventually completely consumed and the current will
decrease to a residual value. Both the potential and the current flow
can be monitored with Chart software in the same way as for
chronoamperometry. The integrated current (that is, the total charge
transferred) can also be determined by integrating the current signal
(see
) and this can be used to determine
the extent of reaction.
If the solution is being stirred during the procedure then eventually all
the substrate can be oxidized, or reduced, to a new material and the
technique may be referred to as electrosynthesis rather than
chronoamperometry.
If the reaction causes the formation of a polymer film on the electrode
(for example pyrrole to polypyrrole, or aniline to polyaniline) then the
technique may be referred to as electropolymerisation.
To effect the electrolysis of a substrate a potential should be chosen
which is at least 50 – 200 mV more oxidising (or reducing) than the
half-wave potential in order to ensure complete reaction. It is usually
important to separate the auxiliary (counter) electrode from the main
body of the electrochemical cell by means of a salt bridge. This is to
prevent the reduction products formed in the region of the auxiliary
electrode reacting with the products of oxidation at the working
electrode (or, if reducing the substrate, to prevent the products of
oxidation forming around the auxiliary electrode from reacting with the
reduction products at the working electrode). The working electrode is
usually constructed to have relatively large surface area so that a
Summary of Contents for e-corder
Page 62: ...58 eDAQ Potentiostats ...
Page 88: ...84 eDAQ Potentiostats ...
Page 94: ...90 eDAQ Potentiostats ...
Page 102: ...98 eDAQ Potentiostats ...
