Electrolytic Cell

What is an Electrolytic Cell?

An electrolytic cell can be defined as an electrochemical device that uses electrical energy to facilitate a non-spontaneous redox reaction. Electrolytic cells are electrochemical cells that can be used for the electrolysis of certain compounds. For example, water can be subjected to electrolysis (with the help of an electrolytic cell) to form gaseous oxygen and gaseous hydrogen. This is done by using the flow of electrons (into the reaction environment) to overcome the activation energy barrier of the non-spontaneous redox reaction.

The three primary components of electrolytic cells are:

• Cathode (which is negatively charged for electrolytic cells)
• Anode (which is positively charged for electrolytic cells)
• Electrolyte

The electrolyte provides the medium for the exchange of electrons between the cathode and the anode. Commonly used electrolytes in electrolytic cells include water (containing dissolved ions) and molten sodium chloride.

Comparison Between Galvanic Cells and Electrolytic Cells

Galvanic Cell (or Voltaic Cell)	Electrolytic Cell
Convert chemical energy into electrical energy.	Consume electrical energy to drive non-spontaneous redox reactions.
Contain negatively charged anodes and positively charged cathodes.	Contain positively charged anode and negatively charged cathode.
Feature spontaneous cell reactions.	Feature non-spontaneous cell reactions.

Diagram and Working of an Electrolytic Cell

Molten sodium chloride (NaCl) can be subjected to electrolysis with the help of an electrolytic cell, as illustrated below.

Here, two inert electrodes are dipped into molten sodium chloride (which contains dissociated Na⁺ cations and Cl^– anions). When an electric current is passed into the circuit, the cathode becomes rich in electrons and develops a negative charge. The positively charged sodium cations are now attracted towards the negatively charged cathode. This results in the formation of metallic sodium at the cathode.

Simultaneously, the chlorine atoms are attracted to the positively charged cathode. This results in the formation of chlorine gas (Cl₂) at the anode (which is accompanied by the liberation of 2 electrons, finishing the circuit). The associated chemical equations and the overall cell reaction are provided below.

• Reaction at Cathode: [Na⁺ + e^– → Na] x 2
• Reaction at Anode: 2Cl^– → Cl₂ + 2e^–
• Cell Reaction: 2NaCl → 2Na + Cl₂

Thus, molten sodium chloride can be subjected to electrolysis in an electrolytic cell to generate metallic sodium and chlorine gas as the products.

Applications of Electrolytic Cells

• The primary application of electrolytic cells is for the production of oxygen gas and hydrogen gas from water.
• They are also used for the extraction of aluminium from bauxite.
• Another notable application of electrolytic cells is in electroplating, which is the process of forming a thin protective layer of a specific metal on the surface of another metal.
• The electrorefining of many non-ferrous metals is done with the help of electrolytic cells.
• Such electrochemical cells are also used in electrowinning processes.
• It can be noted that the industrial production of high-purity copper, high-purity zinc, and high-purity aluminium is almost always done through electrolytic cells.