What Is An Electrode?
The term electrode was derived from two Greek words; “electron” which means amber and “hodos” meaning a way. Electrode therefore, refers to an electricity conducting material that connects nonmetallic parts of a circuit such as electrolytes, air, semiconductors and a vacuum. It is simply the point where the current enters and leaves non metallic parts of a circuit. The electrode by which a current enters an electrochemical cell is called anode while a cathode is the electrode by which the current leaves an electrochemical cell. This article will focus mainly on five different types of electrodes that exist in the world of science.
Electrodes can be grouped into different types which include:
- Metal-metal ion electrode
- Metal-insoluble salt electrode
- Metal-amalgam electrode
- Gas-ion electrode
- Redox electrode
Metal-Metal Ion Electrode
This is an electrode consisting of a pure metal rod or strip that is kept in contact with the solution of a water-soluble salt-containing cation of the same metal. In this case, the electrode having a higher oxidation potential undergoes oxidation and acts on the anode while the electrode with a lower oxidation potential undergoes reduction and acts as the cathode. Electron transfer occurs between the metal atoms of the electrode and the metal ions in the solution
Scenarios of Metal-metal ion electrodes include; a silver rod immersed in a silver nitrate solution and copper rod in a copper sulphate solution These electrodes are poorly polarized. This means that the electrode potential does not change significantly because they have a large exchange current density. They are also reversible to the anions of the salt used to build the electrode.
Metal-Insoluble Salt Electrode
Such an electrode consists of a metal rod coated with one of its insoluble salts which is immersed in a solution containing the anion of the insoluble salt. In this case, electron transfer occurs between the metal atoms of the electrode and the metal ions of the insoluble salt. The cation in the solution should have a standard reduction potential less than that of the electrode in question.
A metal-insoluble salt electrode is said to be reversible with respect to the anions of the insoluble salt. The most common electrodes of this kind include; silver-silver chloride electrode, lead-lead sulphate electrode and mercury-calomel electrode.
There are times when metals such as potassium and sodium are intended to be used as electrodes but then they are too reactive to be used in their pure form. In such a case, it is more convenient to use the metal in the form of amalgams. The reactivity of these metals is normally lowered by dilution with mercury. This electrode is set up by placing the metal-amalgam in contact with a solution containing the metal’s ion.
A gas-ion electrode is set up by immersing an inert metal rod such as platinum or gold in a solution containing the anions or cations of a pure gas, usually hydrogen, chlorine or oxygen that is continuously bubbled through the solution. The inert metal electrode does not participate in the reaction but it simply helps in making electrical contact and to act as a source or acceptor of electrons. Electron transfer occurs between the gas and the ions in solution. Examples of gas electrodes include the standard hydrogen electrode, chlorine gas electrode and the oxygen gas electrode.
They are also referred to as oxidation-reduction electrode. This type of electrode is set up by immersing an inert metal such as gold or platinum into a solution containing ions of the same metal in two different oxidation states. The solution for example, may contain a mixture of ferrous and ferric ions or stannous and stannic ions. The inert metal acts as a source or acceptor of electrons and allows the electrode system to be linked to another electrode to create a complete cell.