Fuel Cells And Working of Fuel Cells

Fuel Cells are receiving prominent attention as clean, efficient and affordable alternative energy technologies for the future. A fuel Cell is the direct energy conversion device in which fuel and a oxidizer undergo a controlled chemical reaction, producing products and supplying electrical current directly to an external circuit. The fuel and oxidizer react in stages on two separate electrodes , a positive electrode called cathode, and a negative electrode called anode. The two electrodes are separated by an electrolyte. The rates of reaction are limited by the time it takes for diffusion of chemical species through the electrodes and the electrolyte and by the reaction kinetics.

Fuel cells are of various kinds. The fuel is hydrogen, which diffuses through the porous anode and reacts on the anode surface with OH- ions, forming water and yielding free electrons, according to

H2 + 2OH- ---------> 2H2O + 2e-

The electrons flow into the external circuit, and water passes on to the electrolyte. On the cathode surface, oxygen fed into the cell combines with water from the electrolyte and electrons from the external circuit to produce OH- ions and water according to

(1 / 2)O2 + 2H2O + 2e- ------> 2(OH)- + H2O

The electrolyte separating the electrodes transports the OH- ions, completing , the circuit, and the water (products) is removed from the cell. The overall reaction is

H2 + (1 / 2) O2 -----------> H2O

which is same as the equation for the highly exothermic combustion reaction.

How ever is fuel cell, only a relatively small amount of heat transfer between the call and its surroundings takes place, and the temperature rise is also relatively much smaller.

Energy is removed from fuel cell as electrical energy, whereas energy is removed from a combustion reaction as heat or as heat and work together. Because the fuel cell operates almost isothermally and continuously , the extent to its conversion of chemical energy to electrical energy is not limited by second law of thermodynamics.

the fuel efficiency is defined as,

E = Delta G / Delta H

which can be less than , equal to, or greater than unity. the work done in a fuel cell can be written as,

W max = FnjV

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