| 23.1 |
| Introduction : |
Commercial cells which are used as sources of electrical energy are of three main types: Primary cells, secondary cells and fuel cells. Primary cells are based on cell reactions which are not reversible. Once the cell reaction is complete, the cell is discharged and cannot be recharged again. Examples: Weston Cd Cell, Leclanche' cell (dry cell) etc. |
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| Secondary cells (storage cells or Accumulators) are galvanic cells in which the cell reactions that produce the current can be reversed by applying an external source of current. These can be discharged and recharged many times until the electrode materials last. Examples: Lead-acid battery, Nickel-Cadmium battery, NiFe cells, etc. The term 'battery' is normally used to denote a number of galvanic cells connected in series. |
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| Fuel cells are also galvanic cells in which the reactants, to be oxidised at the anode (fuels) and reduced at the cathode (oxidants), are provided continuously from external sources and the products are removed as they are formed. In a conventional cell, the reactants form a part of the cell. These are not replenished in primary cells but replenished in secondary cells. |
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