Question

What are fuel cells? How are they different from Galvanic cells? Give the construction of hydrogen-oxygen fuel cells?

Answer 1

The primary objective of a cell is to provide electricity. This is acquired by the movement of electrons between the electrodes of the cell. Fuel cells produce electric current through a chemical reaction but it is not a combustion reaction.

Complete step by step answer:
In recent years, scientists have developed the cells which convert chemical energy of a fuel directly into electrical energy. Such cells are called fuel cells. These are the voltaic cells in which the fuels such as ${{{H}}_{{2}}}{{,CO,C}}{{{H}}_{{4}}}{{,}}{{{C}}_{{3}}}{{{H}}_{{8}}}$ etc. are used to generate electrical energy without the intervention of thermal devices like boiler, turbines etc.
Galvanic cells also convert chemical energy into electrical energy. In this cell, a redox reaction is carried out in an indirect manner and the decrease in free energy during the chemical process appears as electrical energy. An indirect redox reaction is such that the oxidation and reduction reactions are carried out in separate vessels. Therefore, a galvanic cell consists of two half cells namely the oxidation half-cell and reduction half-cell.
Compared to the Galvanic cells, the fuel cells are designed in such a way that the materials to be oxidised and reduced at the electrodes are stored outside the cell and are constantly supplied to the electrodes. One of the most successful fuel cells uses the reaction of hydrogen and oxygen to form water and is known as hydrogen-oxygen fuel cell. It is also called Bacon cell after the name of it’s inventor and it had been used to power the Apollo Moon Missions. The electrode reactions of the fuel cells can be shown as;
${{Anode: [}}{{{H}}_{{2}}}{{(g) + 2O}}{{{H}}^{{ - }}}{{(aq)}} \to {{2}}{{{H}}_{{2}}}{{O(l) + 2}}{{{e}}^{{ - }}}{{] \times 2}} \\\ {{Cathode:}}\;{{ }}{{{O}}_{{2}}}{{(g) + 2}}{{{H}}_{{2}}}{{O(l) + 4}}{{{e}}^{{ - }}} \to {{4O}}{{{H}}^{{ - }}}{{(aq)}} \\\ {{Net}}\;{{reaction: 2}}{{{H}}_{{2}}}{{(g) + }}{{{O}}_{{2}}}{{(g)}} \to {{2}}{{{H}}_{{2}}}{{O(l)}}$
The cell runs continuously as long as the gases are supplied at the temperature ${{525}}\;{{K}}$and ${{50}}\;{{atm}}$ pressure.

Additional information:
Other examples for fuel cells are propane-oxygen fuel cell and methanol-oxygen fuel cell. The advantages of fuel cells include pollution free working and high efficiency.

Note: Fuel cells can act as continuous sources of energy. Because unlike conventional batteries, energy can be obtained from the fuel cell continuously so long as the supply of fuel is maintained.