Auxiliary electrode
Encyclopedia
The Auxiliary electrode, often also called the counter electrode, is an electrode
used in a three electrode electrochemical cell for voltammetric analysis
or other reactions in which an electrical current
is expected to flow. The auxiliary electrode is distinct from the reference electrode
, which establishes the electrical potential against which other potentials may be measured, and the working electrode
, at which the cell reaction takes place.
In a two-electrode system, either a known current or potential is applied between the working and auxiliary electrodes and the other variable may be measured. The auxiliary electrode functions as a cathode whenever the working electrode is operating as an anode and vice versa. The auxiliary electrode often has a surface area much larger than that of the working electrode to ensure that the half-reaction occurring at the auxiliary electrode can occur fast enough so as not to limit the process at the working electrode.
When a three electrode cell is used to perform electroanalytical chemistry, the auxiliary electrode, along with the working electrode, provides circuit over which current is either applied or measured. Here, the potential of the auxiliary electrode is usually not measured and is adjusted to so as to balance the reaction occurring at the working electrode. This configuration allows the potential of the working electrode to be measured against a known a reference electrode without compromising the stability of that reference electrode by passing current over it.
The auxiliary electrode may be isolated from the working electrode using a glass frit. Such isolation prevents any byproducts generated at the auxiliary electrode from contaminating the main test solution: for example, if a reduction is being performed at the working electrode in aqueous solution, oxygen may be evolved from the auxiliary electrode. Such isolation is crucial during the bulk electrolysis of a species which exhibits reversible redox behavior.
Auxiliary electrodes are often fabricated from electrochemically inert materials such as gold, platinum, or carbon.
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
used in a three electrode electrochemical cell for voltammetric analysis
Voltammetry
Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
or other reactions in which an electrical current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
is expected to flow. The auxiliary electrode is distinct from the reference electrode
Reference electrode
A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant concentrations of each participants of the redox reaction.There are many ways reference...
, which establishes the electrical potential against which other potentials may be measured, and the working electrode
Working electrode
The working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
, at which the cell reaction takes place.
In a two-electrode system, either a known current or potential is applied between the working and auxiliary electrodes and the other variable may be measured. The auxiliary electrode functions as a cathode whenever the working electrode is operating as an anode and vice versa. The auxiliary electrode often has a surface area much larger than that of the working electrode to ensure that the half-reaction occurring at the auxiliary electrode can occur fast enough so as not to limit the process at the working electrode.
When a three electrode cell is used to perform electroanalytical chemistry, the auxiliary electrode, along with the working electrode, provides circuit over which current is either applied or measured. Here, the potential of the auxiliary electrode is usually not measured and is adjusted to so as to balance the reaction occurring at the working electrode. This configuration allows the potential of the working electrode to be measured against a known a reference electrode without compromising the stability of that reference electrode by passing current over it.
The auxiliary electrode may be isolated from the working electrode using a glass frit. Such isolation prevents any byproducts generated at the auxiliary electrode from contaminating the main test solution: for example, if a reduction is being performed at the working electrode in aqueous solution, oxygen may be evolved from the auxiliary electrode. Such isolation is crucial during the bulk electrolysis of a species which exhibits reversible redox behavior.
Auxiliary electrodes are often fabricated from electrochemically inert materials such as gold, platinum, or carbon.
See also
- Working electrodeWorking electrodeThe working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
- Reference electrodeReference electrodeA reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant concentrations of each participants of the redox reaction.There are many ways reference...
- Electrochemical cellElectrochemical cellAn electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy. A common example of an electrochemical cell is a standard 1.5-volt "battery"...
- ElectrochemistryElectrochemistryElectrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
- VoltammetryVoltammetryVoltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
Further reading
- http://www.gamry.com/App_Notes/Potentiostat_Primer.htm
- http://www.iupac.org/goldbook/A00535.pdf