degradation) are not chemically reversible (see discussion below
on EC Coupled Reactions). Electrochemical reversibility refers
to the electron transfer kinetics between the electrode and
the analyte. When there is a low barrier to electron transfer
(electrochemical reversibility), the Nernstian equilibrium is
established immediately upon any change in applied potential.
By contrast, when there is a high barrier to electron transfer
(electrochemical irreversibility), electron transfer reactions are
sluggish and more negative (positive) potentials are required
to observe reduction (oxidation) reactions, giving rise to larger
ΔEp. Often electrochemically reversible processeswhere the
electron transfers are fast and the processes follow the Nernst
equationare referred to as “Nernstian.”
Importance of the Scan Rate
The scan rate of the experiment controls how fast the applied
potential is scanned. Faster scan rates lead to a decrease in the
size of the diffusion layer; as a consequence, higher currents
are observed.2,3 For electrochemically reversible electron
transfer processes involving freely diffusing redox species, the
Randles−Sevcik equation (eq 3) describes how the peak current
ip (A) increases linearly with the square root of the scan rate
υ (V s−1), where n is the number of electrons transferred in the
redox event, A (cm2)is the electrode surface area (usually treated
as the geometric surface area), Do (cm2 s−1) is the diffusion
coefficient of the oxidized analyte, and C0 (mol cm−3) is the bulk
concentration of the analyte.
i
0.446
nFAC nF D
⎛
⎝
υ
0 o
1/2
= ⎜ ⎟
p
RT
⎞
⎠
(3)
The Randles−Sevcik equation can give indications as to
whether an analyte is freely diffusing in solution, as explained in
Box2.Asanalytes can sometimes adsorb tothe electrode surface,
it is essential to assess whether an analyte remains homogeneous
in solution prior to analyzing its reactivity. In addition to
verifying that the analyte is freely diffusing, the Randles−Sevcik
equation may be used to calculate diffusion coefficients
(Experimental Module 4: Cyclic Voltammetry of Ferrocene:
Measuring a Diffusion Coefficient).2
■ COLLECTING DATA
Introduction to the Electrochemical Cell
In the experimental section of papers describing electrochemical
measurements, a brief description is generally given for the
experimental setup used to collect the data. The vessel used for a
cyclic voltammetry experiment is called an electrochemical cell.
Aschematic representation of an electrochemical cell is presented
in Figure 4. The subsequent sections will describe the role of each
component andhowtoassembleanelectrochemicalcell to collect
data during CV experiments.
Preparation of Electrolyte Solution
As electron transfer occurs during a CV experiment, electrical
neutrality is maintained via migration of ions in solution.
Aselectrons transfer from the electrode to the analyte, ions move
in solution to compensate the charg
