10-4
10.1
Linear Sweep Techniques (LSV, CV,
LOGI, CYCLE)
In LSV, the potential is varied linearly from an initial potential (Initial E) to a final
potential (Final E) at a constant rate (Scan Rate), and the current is monitored as a
function of the applied potential. The potential wave form for LSV is shown in
Figure 10-1.
QUIET TIME
INIT
E
FINAL
t
Figure 10-1. Potential wave form for LSV.
A more commonly used variation of LSV is CV. In this technique, when the final
potential is reached, the scan direction is reversed and the same potential range is
swept again in the opposite direction. Therefore, the product of the electrochemical
reaction on the forward scan can be examined on the reverse scan. This feature is one
of the main reasons for the widespread use of this technique.
In CV, the potential can be cycled over the same range many times. Three potential
parameters are required; the initial potential (Initial E), and the two switching
potentials (i.e., the potential at which the direction of the scan is reversed), High E
and Low E. The potential wave form for CV is shown in Figure 10-2.
The simplest I-E curve for CV is shown in Figure 10-3. The asymmetry of the curve
is due to the diffusional mass transport. However, there are many other parameters
that can affect the shape of this curve; for example, slow heterogeneous transfer
kinetics, instability of the oxidized or reduced species, and adsorption. If the
heterogeneous electron transfer is rapid (relative to the timescale of the experiment)
and both the oxidized and reduced species are stable (again, on the timescale of the
experiment),then the redox process is said to be electrochemically reversible. The
standard redox potential is the mean of the two peak potentials (E
pa
and E
pc
), and the
