In chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic cell.

History

• 1800 - William Nicholson and Johann Ritter decomposed water into hydrogen and oxygen.
• 1807 - Potassium, Sodium, Barium, Calcium and Magnesium were discovered by Sir Humphry Davy using electrolysis.
• 1886 - Fluorine was discovered by Henri Moissan using electrolysis.
• 1886 - Hall-Héroult process developed for making aluminium
• 1890 - Castner-Kellner process developed for making sodium hydroxide

Overview

Electrolysis is the passage of an electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.

The main components required to achieve electrolysis are:

• A liquid containing mobile ions - an electrolyte
• An external source of direct electric current
• Two solid rods or plates known as electrodes

The components perform the following roles in the electrolysis process:

• The mobile ions are the carriers of electrical current in the liquid (electrolyte). If the ions are not mobile, as in a solid salt then electrolysis cannot occur.
• The externally supplied direct electric current supplies the energy necessary to create or discharge the ions in the liquid or solution. Electric current is carried by electrons in the external circuit.
• The electrodes provide the physical interface between
• The electrical circuit providing the energy to achieve the electrolysis
• The electrolyte containing the ionic materials that are to be separated.

The electrodes must be able to conduct electricity. Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on:

• Chemical reactivity between the electrode and electrolyte
• Cost of manufacture of the electrode

Ancillary practical components to achieve electrolysis include:

• Vessels to supply, contain and remove the reactants and products
• Electrical circuitry

Process of electrolysis

The key process of electrolysis is the interchange of atoms and ions by the removal or addition of electrons from the external circuit. The required products of electrolysis are in some different physical state from the electrolyte and can be removed by some physical process. For example, in the electrolysis of brine to produce hydrogen and chlorine, the products are gaseous. These gaseous products bubble from the electrolyte and are collected.

A liquid containing mobile ions (electrolyte) is produced by