What Does Cyclic Voltammetry (CV) Mean?
Cyclic voltammetry (CV) is an electrochemical method which measures the current that develops in an electrochemical cell under conditions where voltage is in excess of that predicted by the Nernst equation. CV is performed by cycling the potential of a working electrode, and measuring the resulting current.
Cyclic voltammetry can be used to study qualitative information about electrochemical processes under various conditions, such as the presence of intermediates in oxidation-reduction reactions, or the reversibility of a reaction. CV can also be used to determine:
- Electron stoichiometry of a system.
- Diffusion coefficient of an analyte.
- Formal reduction potential.
This technique has been used to investigate corrosion behavior of metals and to analyze the influence of sulphide, sulphate and bicarbonate anions on the pitting corrosion behavior of carbon steel in water containing chloride ions.
Corrosionpedia Explains Cyclic Voltammetry (CV)
A cyclic voltammetry (CV) system consists of:
- Electrolysis cell.
- Current-to-voltage converter.
- Data acquisition system.
The electrolysis cell consists of:
- Working electrode.
- Counter electrode.
- Reference electrode.
- Electrolytic solution.
The current-to-voltage converter measures the resulting current, and the data acquisition system produces the resulting voltammogram.
Cyclic sweeps are used to measure corrosion that proceeds at about the same rate over the entire metal's surface (uniform) and corrosion at discrete sites on the surface, such as pitting crevice and stress corrosion cracking (localized).
Cyclic voltammetry involves applying voltage to an electrode immersed in an electrolyte solution, and seeing how the system responds. In CV, a linear sweeping voltage is applied to an aqueous solution containing the compound of interest. CV provides the capability for generating a species during the forward scan and then determining its outcome with the reverse scan or subsequent cycles, all within seconds. The potential is measured between the reference and working electrodes, and the current is measured between the working and counter electrodes.
To measure uniform corrosion, the method of Tafel extrapolation is used, the Tafel slope being the slope of the straight-line portion of the semi-logarithmic polarization curve. To determine the degree of localized corrosion, the amount of hysteresis between the positive sweep and the negative sweep is calculated.
CV differs from polarography in two important ways:
- The working electrode at which the reactions of interest occur has a constant area, not one which changes with time as in classical polarography.
- The potential of the working electrode is scanned rapidly over a wide potential range and then returned to its initial value using an applied potential signal which varies linearly with time between the initial value and the final value at the limit of the forward scan.