Cyclic voltammetry- principle and theory CV is a potential sweep technique which involves sweeping theelectrode potential between fixed potential limits E1 and E2 at a known sweeprate (scan rate). On reaching the limit E2 the sweep is reversed to E1 toobtain a cyclic scan.
The CV scan is a plot of current versus potential andindicates the potential at which redox process occur. The potential axis isalso a time axis that is related to scan rate 27. The excitation signal forCV is a linear potential scan with triangular waveform as shown in Fig.1.
128. This triangular potential excitation signal sweeps the potential of anelectrode between two values, sometimes called the switching potentialIn cyclicvoltammetry, a species that undergoes a reduction during a cathodicpolarization of working electrode in unstirred solution is re-oxidised byapplying a reverse (anodic) scan. The correlation of the cathodic and anodicpeak currents and differences in cathodic and anodic peak potentials with thevoltage scan rates has been studied mathematically for differentelectrochemical reactions.
The sweep rates in cyclic voltammetry can be aboutthe same as in single sweep voltammetry. The current measured during this processis often normalised to the electrode surface area referred to as the currentdensity. The current density is then plotted against the applied potential, andthe result is referred to as a cyclic voltammogram. A peak in the measuredcurrent is seen at a potential that is characteristic of any electrode reactiontaking place. The peak width and height for a particular process may depend onthe sweep rate, electrolyte concentration and the electrode material 5. To carry out an oxidation process, a positive potential rampis applied and the electroactive species loses an electron at the electrodegiving rise to an anodic peak current (Ipa) which usually gives an oxidationpeak at a given potential (Epa). Cathodic currents (Ipc) are observed when thepotential is applied in the negative direction leading to a reduction process,typically giving a reduction peak at a given potential (Epc).
The CV is usuallyinitiated at a potential where species are not electroactive. The important parameters of a cyclic voltammogramare the magnitudes of anodic peak current (Ipa), the cathodic peak current (Ipc),the anodic peak potential (Epa) and cathodic peak potential (Epc) are shown inFig. 1.2. The results extracted by these parameters can be used to know theinformation on kinetic and thermodynamics of redox system 29. Scanning thepotential in the negative direction makes the electrode a stronger reductant,whereas scanning the potential in the positive direction makes it betteroxidant as shown in Fig.1.
3.
