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.

Click here to learn more about the difference between Galvanic cells and electrolytic cells.

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.

Electrolytic Cell Diagram

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
  • Reaction at Anode: 2Cl → Cl2 + 2e
  • Cell Reaction: 2NaCl → 2Na + Cl

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.

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Frequently Asked Questions – FAQs

What are the key differences between electrolytic cells and Galvanic cells?

The cell reactions of electrolytic cells are non-spontaneous whereas the cell reactions of Galvanic cells are spontaneous. Galvanic cells generate electrical energy from chemical reactions whereas electrolytic cells generate non-spontaneous redox reactions from an input of electrical energy.

What are the three primary components of electrolytic cells?

The three main components of electrolytic cells include the cathode, the anode, and the electrolyte. In electrolytic cells (as is the case in most electrochemical cells), oxidation occurs at the anode and reduction occurs at the cathode.

What kinds of charges are held by the electrodes of electrolytic cells?

In electrolytic cells, the cathode is negatively charged and the anode is positively charged. The positively charged ions flow towards the cathode whereas the negatively charged ions flow towards the anode.

What are the uses of electrolytic cells?

Electrolytic cells can be used to produce oxygen gas and hydrogen gas from water by subjecting it to electrolysis. These devices can also be used to obtain chlorine gas and metallic sodium from aqueous solutions of sodium chloride (common salt). Another important application of electrolytic cells is in electroplating.

How do electrolytic cells work?

When an external electric current flows into the cathode of the electrolytic cell, the resulting negative charge attracts the dissociated positive ions present in the electrolyte. This results in the deposition of the positively charged ions onto the cathode. At the same time, the negatively charged ions flow towards the anode, which is positively charged.

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