What are fuel cells ? Discuss briefly hydrogen-oxygen fuel cell ?

Explanation

Fuel cells. These are voltaic cells in which the reactants are fed continuously to the electrodes. These are designed to convert the energy from the combustion of fuels such as `H_(2),CO,CH_(4)` etc., directly into electrical energy. The common example is hydrogen-oxygen fuel cell as described below:

In this cell, hydrogen and oxygen are bubbled through a porous carbon electrode into concentrated aqueous sodium hydroxide (See Fig.). The diffusion rates of the gases into the cell are carefully regulated to get maximum efficiency. In the anode compartment hydrogen is oxidised while oxygen in the cathode compartment is reduced. The net reaction is the same as burning of hydrogen and oxygen to form water. The reactions are given below :
At anode :
`2[H_(2)(g)+2OH^(-)(aq)to2H_(2)O(l)+2e^(-)]`
At cathode :
`O_(2)(g)+2H_(2)O(l)+4e^(-)to4OH^(-)(aq)`
Overall reaction :
`2H_(2)(g)+O_(2)(g)to2H_(2)O(l)`
The catalysts (Pt, Ag or Coo) are also added. This cell runs continuously as long as the reactants are fed. These fuel cells are more efficient than conventional methods of generating electricity on a large scale by burning hydrogen, carbon fuels because these fuel cells convert the energy of the fuel directly into electricity.
This cell has been used for electric power in the Apollo space programme.