Important parameters:
The important parameters of a cyclic voltammogram are the magnitudes of the anodic peak current ( I pa ) and cathodic peak current ( I pc ), and anodic peak potential ( E pa) and cathodic peak potential ( Epc ). These parameters are labeled in Figure. One method of measuring Ip involves extrapolation of a baseline current as shown in Figure. The establishment of correct baseline is essential for the accurate measurement of peak currents. It is commonly hard for more complicated systems. The peak current for a reversible system is described by the Randles-Sevcik equation for the forward sweep of the first cycle.
iP = (2.686 ×105 ) n3/2 AD1/2C0v1/2
where ip is peak current in ampere, n is electron stoichiometry, A is area of the electrode (cm2), here D is diffusion coefficient (cm2/second) and Co is the concentration (mol/cm3), and v is scan rate (v/second)
ip α Co if all the parameters are kept constant. The relationship to concentration is particularly important in analytical applications and in studies of electrode mechanism.
The value of I p a and Ip c should be identical for a simple reversible (fast) couple i.e.
Ipc/ I pa = 1
According to Eq. (7.8), Ip increases with v1/2. . Therefore, the ratio of peak currents can be significantly affected by chemical reactions coupled to the electrode process.
A redox couple in which both species rapidly exchange electrons with the working electrode is called an electrochemically reversible couple. The formal reduction potential (E0′) for a reversible couple is centered between Epa and Epc.
E0′ = Epa + Epc /2
The number of electrons transferred in the electrode reaction (n) for a reversible couple can be determined from the separation between peak potentials.
?Ep = Epa- Epc = 0.059/n
Thus, for a one-electron process, such as the reduction of [FeIII(CN)6]3- to [FeIII(CN)6]3-, exhibited ? Ep of 0.059 V. Slow electron transfer at the electrode surface, "irreversibility" causes the peak separation ( ? E) to increase.