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Voltammetry: Overview

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In voltammetry, the current flowing through an electrochemical cell is measured as a function of applied potential under conditions of concentration polarization.

The voltammetric cell comprises three electrodes immersed in a dilute solution of the analyte along with a supporting electrolyte.

A potentiostat varies the working electrode's potential relative to the reference electrode. The resulting current is recorded against the working electrode potential as a voltammogram.

Working electrodes in voltammetry have minimal surface areas to enhance polarization.

Generally, mercury working electrodes are preferred for their relatively large negative potential range because of the high overvoltage of hydrogen on mercury.

Additional advantages include amalgam formation and the ability to renew the electrode surface by new drop formation.

In dilute solutions, the current that results when an electroactive species is reduced or oxidized reaches a limiting value directly proportional to the analyte's concentration. By measuring voltage and current at the interface between the electrode and an electroactive analyte, voltammetry reveals information about the reduction or oxidation processes of the analyte.

Overview

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Voltammetry is an electroanalytical technique in which the current flowing through an electrochemical cell is measured as a function of applied potential, typically under conditions of concentration polarization. The technique provides valuable information about redox-active species, and the current response is plotted as a voltammogram.

A voltammetric cell uses three electrodes: a working electrode, a reference electrode, and an auxiliary electrode. The redox reactions occur in the working electrode, and a potentiostat controls its potential. Mercury electrodes are frequently used as working electrodes due to their wide negative potential range, which minimizes interference from hydrogen evolution. Mercury electrodes can form amalgams with various metals, enhancing certain redox reactions. In addition, their surface can be renewed by forming new drops, maintaining accuracy. Common types include the hanging mercury drop electrode (HMDE) and the dropping mercury electrode (DME).

The reference electrode, such as the saturated calomel electrode or silver-silver chloride electrode, plays a crucial role in voltammetry. It maintains a constant potential, ensuring accurate measurement. The auxiliary electrode, often a platinum wire, completes the circuit.

Mercury electrodes are preferred in many applications due to their large negative potential range, which prevents unwanted hydrogen reduction, and their ability to form amalgams. Their versatility and the ability to renew the electrode surface ensure consistent and reliable results during measurements.

Voltammetry is widely applied in environmental monitoring (e.g., detecting trace metals), pharmaceutical analysis, and electrochemical sensor development. By analyzing the current response, voltammetry helps determine the concentration of electroactive analytes in the solution. In dilute solutions, the current reaches a limiting value directly proportional to the analyte's concentration, making this technique highly valuable for quantitative analysis.

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Electroanalytical Technique

Working Electrode

Reference Electrode

Auxiliary Electrode

Mercury Electrode

Hanging Mercury Drop Electrode

Dropping Mercury Electrode

Saturated Calomel Electrode

Silver Silver Chloride Electrode