Electrochemical Cells – Electrolytic and Galvanic Cells

A new chapter in electrochemistry began with the findings of Alessandro Volta. He discovered his first battery which was a voltaic pile in 1800. Initially, Galvani said that electricity was produced from animals. His experiment was when he brought in metal in close contact with the frog’s leg and the frog’s leg contracted. But Volta’s assumption was that when two dissimilar metals were kept in contact by a conductor, electricity was produced. He also demonstrated his idea. His volcanic pile consisted of zinc and silver plates that were kept in contact using brine-soaked cardboard. The brine acted as an electrolyte with copper and zinc plates as electrodes. This invention of Alessandro has led to a revolution and today’s modern battery was built on this idea. Volta also arranged metals in a series of ranks. From the series, if two metals are farthest then that combination of metals produces maximum electricity. Later it was found that his series was similar to that of the arrangements in the periodic table.

Electrochemical cells

What is an Electrochemical Cell? An electrochemical cell is a device where redox reactions are performed and release electricity. Redox reaction is nothing but oxidation and reduction reactions. In general, the chemical reaction in which electrons are transferred is called a redox reaction.

The three main components of electrochemical cells are Cathode, Anode, and Electrolyte. The cathode and anode are together called electrodes. These electrodes are made of either conducting metals or semiconductors or a conductive polymer.

Cathode

• A cathode is an electrode that is positively charged.
• In an electrochemical cell, reduction occurs at the cathode.
• As the cathode is positively charged electrons move towards the cathode.
• It receives electrons.

Anode

• An anode is an electrode that is negatively charged.
• In an electrochemical cell, oxidation occurs at the anode.
• As the anode is negatively charged electrons move from the anode.
• It is the donor of electrons.

Electrolyte

The electrolyte is nothing but a solution of water in which the electrolyte is dissolved. The electrolyte is something that has ions in it. The most commonly known electrolyte is a salt solution. That is a sodium chloride solution. In sodium chloride solution sodium is positively charged and chloride is negatively charged. Thus they act as a good electrolyte in an electrochemical cell. It is dissolved in water to facilitate the motion of electrons.

Type of electrochemical cell

There are two types of electrochemical cells that are commonly used. They are galvanic cells and electrolytic cells. The galvanic cell is named after the scientist Lugi Galvani. 

Galvanic Cells or Voltaic Cell

The galvanic cell is also called voltaic cells. The galvanic cells principle is used in modern batteries that we use today. The cell in which chemical energy is converted into electrical energy is called a galvanic cell. In galvanic cells, the cathode acts as the positive electrode and the anode acts as the negative electrode. In galvanic cells, the half cells i.e. Electrochemical cells with one electrode are immersed in a solution in different containers. The electrodes are connected through salt bridges. When spontaneously the ions move from one electrode to the other electrical energy is produced. That energy can be used for some useful work.

Electrolytic cells

The reverse mechanism of a galvanic cell is an electrolytic cell. In an electrolytic cell, electrical energy is utilized for the motion of ions inside the electrolyte. Electrolysis is the process that takes place in an electrolytic cell for producing electrical energy. Thus electrical energy is consumed to produce chemical energy. As an electrolytic cell is the reverse of a galvanic cell in an electrolytic cell, the cathode is marked with the negative terminal and the anode is marked with a positive terminal. In electrolytic cells the redox reaction is not spontaneous as redox reactions happen only when electrical energy is passed through electrodes. This principle is mainly used in electroplating methods.

There is one more classification for electrochemical cells based upon the nature of chemical reaction. That is reversible or irreversible. Based on that, the cells are classified as primary and secondary electrochemical cells. 

Primary cell

Primary cells are a type of electrochemical cell that can be used only once. We cannot recharge those types of electrochemical cells for further use. The electrodes are well insulated in primary cells. They are very cheap compared to rechargeable batteries. A constant supply of electricity could be produced. But the constant supply could be produced only for a short span of time. After which the entire cell has to be replaced. The primary cell functions as a galvanic cell.

Example of a primary cell is a dry cell.

Secondary cells

Secondary cells are rechargeable batteries. They can be recharged for many cycles. These batteries are expensive when compared to secondary batteries. They cannot produce a constant supply of energy. They produce electrical energy for a longer period. They can supply high energy and low energy. The secondary cell can act as both a galvanic cell and electrolytic cell.

Example for a secondary cell is a lead accumulator.

Fuel cell

Fuel cell is a special type of cell. Like normal electrochemical cells it has both electrodes i.e. anode and cathode and an electrolyte. But unlike other cells it can produce electricity until there is a supply of fuel. The most commonly used fuel is hydrogen. They are eco-friendly as they produce non-polluting water as a by-product. In practice a large stack of fuel cells is packed to produce the required amount of electricity. Because a single hydrogen cell can produce only a small amount of electrical energy. There was much research taking place for using hydrogen fuel cells for automobiles. 

Conclusion

There are many applications for electrochemical cells. A galvanic cell is used as the battery that we use today. The best example is the batteries that we use in torch lights, TV remotes, etc. Batteries are used in a variety of ways. We use lithium batteries and lead acid batteries in automobiles. Electrolytic cells are also used in a wide range of applications. The electrolysis process is performed to do electroplating. To produce high purity metals such as aluminum,  copper, zinc the electrolytic cell’s process is used. Recently electrochemical cells were found to be used as lights. The light-emitting electrochemical cells are discovered. They consume low energy and are luminous with good efficiency.