Many electronic devices used by humans are powered by batteries that generate electricity from chemical reactions. These devices that convert chemical energy into electrical energy are commonly referred to as Electrochemical Cell. An example of such a cell is the common AA battery.
Electrochemical cells that generate electricity from spontaneous redox reactions are known as Voltaic cells or Galvanic cells (named after the Italian physicists Alessandro Volta and Luigi Galvani respectively). They are generally made up of two different metals that are connected by a salt bridge. Electrolytic cells are the electrochemical cells that consume electrical energy in order to drive a redox reaction that is not spontaneous.
Electrochemical cells can be broadly classified into two categories – primary cells and secondary cells.
Primary cells are the electrochemical cells that generate electrical energy from irreversible reactions. These cells cannot be recharged once the reactants are completely consumed, and must be discarded when depleted. Common examples of primary cells include use-and-throw galvanic batteries.
The electrochemical cells in which the cell reaction is reversible are commonly referred to as secondary cells. These cells can be run as both electrolytic cells and galvanic cells. They are also known as rechargeable batteries.
Most electrochemical cells consist of two half-cells, which are made up of an electrode dipped in an electrolyte. These half-cells are generally connected by a salt bridge, which provides a platform for ionic contact. Oxidation occurs in one half of the cell whereas reduction occurs in the other. Once chemical equilibrium is reached, the net voltage of the electrochemical cell reaches zero and the production of electricity is halted.
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