An electrochemical cell is a device consisting of two metallic electrodes dipping into the solutions of the same or different electrolytes which convert either electrical energy into chemical energy or chemical energy into electrical energy. In this cell, electrochemical reactions take place which involve the transfer of electrons from the metal to species in solution.
Electrochemical cells are systems made up of two metallic electrodes that are submerged/dipped in the same or different electrolytes in electrical communication. These cells perform two functions either, convert chemical energy into electrical energy or convert electrical energy into chemical energy. On the basis of function, these are classified as electrolytic and galvanic cells.
What is the difference between a cell and a battery? A cell is a single arrangement of two electrodes and an electrolyte that can produce electrical energy as a result of a chemical reaction occurring inside the cell or can produce a chemical reaction as a result of electricity passing through the cell. Whereas. a battery is a combination of two or more cells arranged in series or parallel.
Types of electrochemical cells
There are two types of electrochemical cells.
- Electrolytic cell
- Galvanic cell( Voltaic cell)
An electrolytic cell is a device in which physical or chemical changes occur due to an external supply of electrical energy. An electrolytic cell is used for the purification of metals. Examples: Extraction of sodium from the molten sodium chloride( Dow’s process), Electrorefinement of blister copper, electrolysis of an aqueous solution of HCl into H2 and Cl2, etc.
Let us consider an electrolytic cell involving the electrolysis of molten sodium chloride using the platinum electrode. One electrode is connected to the negative terminal of an external battery which supplies electrons to the metal electrode. Similarly, another electrode is connected to the positive terminal of the battery. When electricity is passed, the ions present in the solution carry electricity within the solution.
Positive ions i.e cations are attracted towards the negative electrode(cathode) and negative ions i.e anions are attracted towards the positive electrode( anode) as shown in the figure.
Reduction takes place at cathode while oxidation takes place at anode. The corresponding electrode reactions are represented as:
A galvanic cell is a device in which electrical energy is produced due to the occurrence of some physiochemical process in the cell. Example: Dry cell, lead storage battery, Daniel cell, etc.
If the emf produced is due to net chemical reaction occuring in the cell, then it is said to be chemical cell. Whereas, if the emf is due to the transfer of matter from one part to another part, then it is said to be concentration cell. Further, depending upon wheather, there exists actual contact of two solutions or not, the cells are classified as cell with or without transference.
Electrolytic cell Vs Galvanic cell
The main difference between the electrolytic cell and galvanic cell is that the electrolytic cell consumes electrical energy and brings chemical changes while the galvanic cell produces electrical energy due to the occurrence of a chemical reaction or physical changes in the cell. More differences between these two types are listed below:
|Electrolytic cell||Galvanic cell|
|It is a device that converts electric energy into chemical energy.||It is a device that converts chemical energy into electrical energy.|
|Redox reaction is non-spontaneous.||It is based on a redox reaction which is spontaneous.|
|The two electrodes are set up in a solution of the same electrolyte.||The two electrodes may be set up in the solution of the same or different electrolyte.|
|The electrode which is connected to the –ve terminal of the battery is called cathode(-) where reduction takes place and another electrode is the anode(+).||The electrode on which oxidation takes place is called the anode(-) and reduction takes place in the cathode(+).|
|A Salt bridge is not required.||A Salt bridge is used.|
|Ions are discharged on both electrodes.||Ions are discharged only on the cathode.|