Cyclic voltammetry is a type of potentiodynamic electrochemical measurement, a technique used to measure potential at an electrode in an electrochemical cell.
Cyclic voltammetry is based on a linear potential waveform where potential is changed as a linear function of time. The potential range of a substance is scanned starting at the initial potential and ending at the final potential. The direction of the potential scan is then reversed, and the potential range is scanned again back to the point of initial potential. Depending on the experiment being conducted, several cycles of scanning can take place.
This technique is one of the most effective and versatile methods used for acquiring information about electrochemical reactions, and is often the first experiment performed in an electrochemical study. It has the benefit of offering a rapid calculation of redox potentials. Redox potential is a measure in volts of the affinity of a specified substance for electrons compared with hydrogen, otherwise known as its electronegativity.
The atoms of every element differ in their affinity for electrons. For example, Fluorine is the most electronegative element. The relative electronegativity of two atoms of different elements will in part determine what kind of chemical bond will form between those elements. Two elements with a large difference in their electronegativity will form an ionic bond, where one element donates electrons to the other. Two elements with only a small difference in electronegativity will form a covalent bond where atoms will share electrons.
To perform a cyclic voltammetry experiment, electrodes are applied to a solution forming an electrochemical cell. This cell will have a unique, measurable potential determined by what materials are used, and will vary for different materials. Current is determined and plotted as a function of the potential applied to the working electrode. Electrode potential will ramp linearly, versus time.
In an electrochemical cell used for electroanalytical measurements there are three electrodes that will be used. These are the reference electrode, the counter electrode, and the working electrode. The working electrode is the indicating electrode, at which the electrochemical process being measured takes place. The reference electrode is the electrode at which the potential is constant, creating a reference standard for the experiment. The counter electrode is a source, or sink, for electrons so that a current can be introduced to the cell. The current is measured between the working electrode and the counter electrode. The current will increase as the potential reaches the reduction potential of the solution, and then decreases. It is the current at the working electrode that is plotted as a result.
Cyclical voltammetry is generally used to study the electrochemical properties of an analyte in solution. An analyte itself cannot be measured, rather a measurable property of the analyte is measured, such as the concentration of the analyte or its conductivity.
Sources:
tutorgig.com
Dr. Alf Bacher, UCLA, 2003
