This is a very new concept in the field of energy . The conventional energy generators were having a maximum efficiency of approximately 52%. Which is very low . Most of the energy in that system was dissipated in the form of heat lost to the surroundings and in overcoming the frictional forces of the machines.
These are the cells that convert the energy of combustion of fuels directly into the electric energy.
The efficiency of fuel cells are quite higher it lies between 70 to 85%. That is quite higher than the conventional machines.
These are used in the space shuttles and rockets .
These cells provide continuous supply of current And do not cause any pollution. The continuous supply and optimum pressure has to be maintained to get best results.