Cyclic voltammeter is frequently adopted to study electron transfer in electrochemistry, battery, electrochromic, semiconducting devices fields.
cyclic voltammetry setup
Cyclic voltammeter cell have three electrodes, working electrode, reference electrode, counter electrode, immersed in electrolyte solution.
Supporting electrolyte
Electrolyte is dissolved in the solvent to reduce the solution resistance. Commonly used electrolyte are ammonium salts, e. g. tetrabutylammonium (+NBu4). The choice of counter anion includes [B(C6F5)4]̄, [B(C6H5)4]̄, [PF6]̄, [BF4]̄, and [ClO4]̄. The more coordinating the anion, the more likely it is to have unwanted interactions with the cation, the solvent, or the analyze. An example is t0.25 M [NBu4][PF6] in CH3CN.
Electrodes
Glassy carbon electrodes are frequently used as working electrodes (WE). The cleanness of their surfaces is very critical for the accuracy of the measurement since WEs carry out the electrochemical event of interest. Special attention needs to be paid on the surface polishing and pretreatment.
Reference Electrode (RE) needs to have a well defined and stable equilibrium potential. It is used as a reference point against which the potential of other electrodes can be measured in an electrochemical cell. Common reference electrodes used in aqueous media include the saturated calomel electrode (SCE), standard hydrogen electrode (SHE), and the AgCl/Ag electrode.
The potential of reference electrodes can vary, due to the variations in ion concentration, electrolyte, or solvent used; therefore an internal reference compound with a known E0′, e. g. Ferrocene, is commonly included in all measurements as an internal standard.
Counter electrode (CE) is used to complete the electrical circuit. Current is recorded as electrons flow between the WE and CE. A platinum wire or disk is typically used as a counter electrode, though carbon-based counter electrodes are also available.
Cyclic Voltammogram
The above figure shows an example of cyclic voltammogram and explains the mechanism behind of it.
The Nernst equation relates the potential of an electrochemical cell (E) to the standard potential of a species (E0) and the relative activities of the oxidized (Ox) and reduced (Red) analyte in the system at equilibrium. In the equation, F is Faraday’s constant,R is the universal gas constant, n is the number of electrons, and T is the temperature.
If the reduction process is chemically and electrochemically reversible, the difference between the anodic and cathodic peak potentials, called peak-to-peak separation (ΔEp), is 57 mV at 25 °C (2.22 RT/F), and the width at half max on the forward scan of the peak is 59 mV.
current
Peak current, ip (A) can be influenced by electrode surface area, diffusion coefficient, analyte concentration, scan rate, number of electrons transferred, and temperature, as shown in the following equation. v is scan rateυ (V s−1), n is the number of electrons transferred in the redox event, A (cm2) is the electrode 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.
The content are based on the reference (J. Chem. Educ. 2018, 95, 197−206) and more detailed information be obtained from there.