Modern potentiostat:

Modern potentiostat utilize a three-electrode system as shown in Figure. A potentiostat applies the desired potential between a working electrode and a reference electrode. The working electrode is the electrode on which the electrolysis of interest takes place. The current required to sustain the electrolysis at the working electrode is provided with the help of an auxiliary electrode.  This arrangement prevents large current from passing through the reference electrode that could change its potential. A normal polarographic cell may be used in this technique. Such cells usually consist of glass container with a cap having holes for introducing electrodes and for the passage of pure nitrogen gas for the removal of oxygen from the test solution similar to polarography. A reference electrode is classically a SCE in an Ag/AgCl electrode that is frequently isolated from the solution with a salt bridge to prevent contamination by leakage from the reference electrode. An auxiliary electrode is commonly a platinum wire which is placed directly into the solution. Because the limiting (peak) current in all the voltammetric techniques is temperature dependent, the cell should be thermostated. Cells are commercially available that may require as little as 1-2 ml of the test solution. Thin-layer cells enable voltammograms to be recorded on down to 60 µ l.

A large variety of working electrodes have been used in voltammetry. The dropping mercury electrode is used especially in polarography and the hanging mercury drop electrode (HMDE) in cyclic voltammetry. The thin coat of mercury can be deposited on a substrate such as graphite to form a mercury film electrode (MFE). A significant advantage of mercury is its good negative potential range. Solid electrode such as platinum, gold, glossy carbon, wax impregnated graphite and carbon-paste are also used in cyclic voltammetry. Such electrodes have a better positive potential range than mercury.