Cyclic a known sweep rate (scan rate). On reaching

Cyclic voltammetry- principle and theory

CV is a potential sweep technique which involves sweeping the
electrode potential between fixed potential limits E1 and E2 at a known sweep
rate (scan rate). On reaching the limit E2 the sweep is reversed to E1 to
obtain a cyclic scan. The CV scan is a plot of current versus potential and
indicates the potential at which redox process occur. The potential axis is
also a time axis that is related to scan rate 27. The excitation signal for
CV is a linear potential scan with triangular waveform as shown in Fig.1.1
28. This triangular potential excitation signal sweeps the potential of an
electrode between two values, sometimes called the switching potentialIn cyclic
voltammetry, a species that undergoes a reduction during a cathodic
polarization of working electrode in unstirred solution is re-oxidised by
applying a reverse (anodic) scan. The correlation of the cathodic and anodic
peak currents and differences in cathodic and anodic peak potentials with the
voltage scan rates has been studied mathematically for different
electrochemical reactions. The sweep rates in cyclic voltammetry can be about
the same as in single sweep voltammetry. The current measured during this process
is often normalised to the electrode surface area referred to as the current
density. The current density is then plotted against the applied potential, and
the result is referred to as a cyclic voltammogram. A peak in the measured
current is seen at a potential that is characteristic of any electrode reaction
taking place. The peak width and height for a particular process may depend on
the sweep rate, electrolyte concentration and the electrode material 5.

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To carry out an oxidation process, a positive potential ramp
is applied and the electroactive species loses an electron at the electrode
giving rise to an anodic peak current (Ipa) which usually gives an oxidation
peak at a given potential (Epa). Cathodic currents (Ipc) are observed when the
potential is applied in the negative direction leading to a reduction process,
typically giving a reduction peak at a given potential (Epc). The CV is usually
initiated at a potential where species are not electroactive.

The important parameters of a cyclic voltammogram
are the magnitudes of anodic peak current (Ipa), the cathodic peak current (Ipc),
the anodic peak potential (Epa) and cathodic peak potential (Epc) are shown in
Fig. 1.2. The results extracted by these parameters can be used to know the
information on kinetic and thermodynamics of redox system 29. Scanning the
potential in the negative direction makes the electrode a stronger reductant,
whereas scanning the potential in the positive direction makes it better
oxidant as shown in Fig.1.3.