Definition - What does Auxiliary Electrode mean?
An auxiliary electrode is a special electrode used in a three-electrode electrochemical cell for voltammetric analysis. The three-electrode system is made by the working, reference and auxiliary electrodes.
It can also be used in other reactions where a current is expected to flow. The auxiliary electrode is used to make a connection to the electrolyte for the purpose of applying a current to the working electrode. The material used to make an auxiliary electrode must be an inert material like graphite or a noble metal such as gold, carbon or platinum. This is necessary to prevent it from dissolving in the electrolyte.
An auxiliary electrode is also known as a counter electrode.
Corrosionpedia explains Auxiliary Electrode
An experiment to demonstrate this must have at least two electrodes: the working electrode and another electrode, which acts as the other half of the cell. Apart from applying the desired potential in a controlled way, the working electrode also makes a contact with the analyte. It also facilitates charge transfer to and from the analyte. The second electrode balances the removed or added charge by the working electrode.
This electrode is isolated from the working electrode by the use of a glass frit. This prevents byproducts of the auxiliary electrode from contaminating the test solution. When a reduction occurs in an aqueous solution and at the working electrode, oxygen is evolved at the auxiliary electrode.
The work of the auxiliary electrode is to pass all the current so that the current at the working electrode can be controlled. This is achieved by swinging to extreme potentials at the solvent window edges where the oxidation or reduction of the solvent occurs.
The disadvantage of this experiment is that it does not maintain a constant potential during the passing of the current in countering redox reaction. This problem can be solved by dividing the role of supplying electrons as well as referencing the potential between two different electrodes. The reference electrode is the half cell that has a known reduction potential. Its role is to reference when measuring and controlling the potential of the working electrode. This reference electrode does not pass any current.