Electrochemical cells are devices that are used to convert chemical energy into electrical energy or to convert electrical energy into chemical energy. Electrochemical cells (not to be confused with unit cells) can be used to:

• Generate electricity from the chemical reactions taking place in it
• Spark a chemical reaction by supplying the activation energy in the form of electric current

The electrochemical cells that are used to convert chemical energy into electrical energy are called galvanic cells or voltaic cells. On the other hand, an electrolytic cell is an electrochemical cell that uses electrical energy to generate chemical reactions.

Primary Cell

Electrochemical cells in which the cell reaction is irreversible are called primary cells. These cells are designed to be discarded after use (and are, therefore, associated with the term ‘use-and-throw batteries’). During the lifetime of a primary cell, the reactant chemicals that are used in the electrochemical reaction are slowly depleted. Once the reactant is completely depleted, the cell becomes incapable of generating an electric current. It can be noted that primary cells usually contain highly toxic heavy metals and other contaminants, which makes their disposal very difficult. Furthermore, the energy efficiency of these cells is usually very low (it takes approximately 50 times the maximum energy capacity of a primary cell to manufacture it). For these reasons, primary cells are widely regarded as environmentally unfriendly and outdated. 

Secondary Cell

A secondary cell is an electrochemical cell that can function as both a galvanic cell and as an electrolytic cell. In such a cell, the chemical reaction can be used to generate electricity until the reactants run out, after which it can be charged as an electrolytic cell by passing an electric current through it and regenerating the lost reactants. 

Fuel Cell

Fuel cells are electrochemical cells that convert the chemical energy produced in the reaction between hydrogen fuel and an oxidizing agent into electrical energy. An important example of fuel cells is the hydrogen fuel cell.

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