By Sunil Bhardwaj

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Almost all the electricity produced at present time is by the direct use of coal, oil or natural gas. The fuel is burnt and heat liberated in combustion is used to produce steam which in turn drives the turbine and generator produce electricity. However, the efficiency is about 40%. If by some means electricity is directly produced by the oxidation of fuel in galvanic cell, efficiency is greater than 75%. Hydrogen and Hydrazine N2H4 are used as fuels in cells operated at low temp.

Principle: Direct oxidation of fuels in galvanic cells.

Construction: In the hydrogen - oxygen fuel cell, E, is supplied to anode and an oxidant usually oxygen is supplied to the other electrode (cathode). The electrodes are hollow tubes of porous compressed graphite (carbon). Finely divided Pt. is incorporated into anode. Ag, is incorporated into cathode, These substances acts as the catalyst for the reaction take place at the electrodes.. Acids R alkali can be used as the electrolytes.

Working: When the cell is in operation the reaction take place as follow:

At L.H.E : $$ 2{ H }_{ 2 } \longrightarrow 2{ H }^{ + } + 2{ e }^{ - }\qquad (ox).$$ At R.H.E : $$ \frac { 1 }{ 2 } { O }_{ 2 } + 2{ H }^{ + } + 2{ e }^{ - } \longrightarrow 2{ H }_{ 2 }O\qquad (red).$$ The Net Cell Reaction is,$$ 2{ H }_{ 2 } + \frac { 1 }{ 2 } { O }_{ 2 } \longrightarrow 2{ H }_{ 2 }O $$Hydrogen and oxygen fuel cell is known as Bacon Cell. The emf of the cell is 1.0 - 1.1 volt. They are used in space vehicles i.e. in satellites.

Representation: $$\circleddash Graphite, { H }_{ 2 } | \underset { (aq) }{ KOH } | { O }_{ 2 }, Graphite\oplus $$The main disadvantage of using these cells on large scale is the storing of H2, which is explosive and Pt.is quite costly.