The technique provides qualitative information about electrochemical
reactions, e.g. the redox behaviour of compounds and the kinetics of electron
transfer reactions. In practice, a triangular potential waveform is applied
linearly to the working electrode in a unstirred solution. After a few seconds,
the ramp is reversed and the potential is returned to its initial value. The
process may be repeated several times. The resulting plot of current versus
potential is termed a cyclic voltammogram. Fig. 34.9 shows a typical cyclic
voltammogram for a reversible redox couple after a single potential cycle. It
is assumed that the oxidized form, O, is the only species present at the start.
Therefore, the first scan is towards the (more) negative direction,
commencing at a value were no reduction occurs. As the applied potential
approaches the characteristic E°
for the redox process, a catholic current
starts to increase, up to a maximum. After exceeding the potential at which
the reduction process takes place, the direction of the potential current is
reversed. During this stage, reduced molecules R, generated during the initial
process, are reoxidized back to O, resulting in an anodic peak.
|Fig. 34.9 A typical cyclic voltammogram for a reversible
O + ne− ↔ R redox process.