4.7 Battery-A Source of Electrical Energy
A battery is a galvanic cell, or a group of galvanic cells joined in series. It generates electric current by a redox reaction. When connected in a circuit its anode is oxidised by releasing electrons. These electrons through the external circuit begin to flow towards the cathode. At the cathode, these electrons reduce the oxidizing agent present in the electrolyte. Examples of batteries are dry cells, storage cells, mercury batteries etc.
Fuel Cell
A fuel cell is a special type of galvanic cell which is based upon the reaction between oxygen and a gaseous fuel hydrogen. When hydrogen burns in air, an exothermic reaction occurs and a lot of chemical energy is released in the form of heat and light. In this reaction, hydrogen is oxidized to water.
The energy released from the reaction of hydrogen with
oxygen to form water is converted to electrical energy. A hydrogen- oxygen fuel cell has three compartments separated from one another by porous carbon electrodes. These electrodes contain platinum as a catalyst. The middle compartment contains a hot aqueous solution of KOH. Hydrogen gas is passed through the anode compartment and oxygen is passed through the cathode compartment. At the anode, hydrogen is oxidized to water and at the cathode oxygen is reduced to hydroxide ions.
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