Voltammetry
Electroanalytical method measuring current versus applied potential.
Voltammetry refers to a group of electroanalytical techniques used in analytical chemistry and industrial settings. It works by measuring the electrical current that flows as the voltage applied to a system is changed. The results are displayed as a voltammogram, a graph that shows the current from the analyte against the potential of the working electrode.
The method is considered dynamic because the applied potential changes over time, and the resulting current shifts are recorded. Most experiments involve controlling the voltage of an electrode that touches the analyte, while the current produced is measured. The reactivity of the analyte at the electrode surface helps determine its concentration.
These experiments rely on electrochemical cells to drive the analyte’s redox reactions. Like any such cell, two half-cells are needed—one for reduction and one for oxidation. The setup includes the analyte solution, an ionic electrolyte, and two or three electrodes. Oxidation and reduction happen at the interfaces between the electrodes and the solution. When a species is oxidized, it loses electrons, which travel through an external circuit to generate current and serve as an electron source for reduction. The resulting currents are faradaic, meaning they obey Faraday’s law: the amount of substance produced or consumed at an electrode is proportional to the electric charge passed. This allows the current to be used to find the analyte’s concentration. Whether the analyte is reduced or oxidized depends on the substance and the applied potential, but the reaction always occurs at the working (or indicator) electrode. The potential of this electrode changes with the analyte’s concentration. A second electrode, called the counter or auxiliary electrode, completes the circuit. A third, the reference electrode, provides a stable baseline potential for comparison. With very small microelectrodes, the counter and reference can be combined, because the tiny current flowing through them does not disturb the reference potential.
In a typical three-electrode system, the working electrode applies a controlled potential and transfers charge to or from the analyte. The reference electrode has a known reduction potential and does not pass current; it only serves as a reference for measuring the working electrode’s potential. The auxiliary electrode passes the current needed
- field
- Electroanalytical chemistry
- known_for
- Measuring current as a function of applied potential to determine analyte concentration
- method_type
- Dynamic electrochemical method
- key_components
- Working electrode, reference electrode, auxiliary electrode
Lore & Background
Voltammetry is the study of current as a function of applied potential. Voltammetric methods involve electrochemical cells and investigate the reactions occurring at electrode/electrolyte interfaces. The reactivity of analytes in these half-cells is used to determine their concentration. It is considered a dynamic electrochemical method as the applied potential is varied over time and the corresponding changes in current are measured. Most experiments control the potential of an electrode in contact with the analyte while measuring the resulting current.
Reader's Guide
Voltammetry is significant as a fundamental electroanalytical technique for determining analyte concentrations through faradaic currents, which follow Faraday's law. The method relies on a three-electrode system—working, reference, and auxiliary—to precisely control potential and measure current. The working electrode contacts the analyte and facilitates charge transfer, while the reference electrode provides a constant baseline potential, and the auxiliary electrode passes the current needed to balance the system. Voltammograms, which plot current versus potential, yield key data such as limiting or peak current, used with mathematical models like the Nernst equation to quantify analytes. The technique's legacy includes its widespread use in analytical chemistry and industrial processes, with variations such as polarography using mercury electrodes. The supporting electrolyte minimizes solution resistance and ensures diffusion-controlled reactions, enhancing accuracy.
Did You Know?
- Voltammetry is considered a dynamic electrochemical method because the applied potential is varied over time and the corresponding changes in current are measured.
- The generated currents in voltammetry are faradaic currents, which follow Faraday's law, allowing analyte concentrations to be determined.
- In a three-electrode system, the reference electrode does not pass any current; its only role is to act as a reference for measuring and controlling the working electrode's potential.
- For non-aqueous work, IUPAC recommends the use of the ferrocene/ferrocenium couple as an internal standard.
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