18.0 Fuel Cell

  Electrochemistry

Now a days, manufacturing of cells in which reactants are fed continuously to the electrodes and products are removed continuously from the electrolyte compartment is possible.

A galvanic cell directly converts chemical energy into electricity and is highly efficient. Galvanic cells that are designed to convert the energy of combustion of fuels like hydrogen, methane, methanol, etc. directly into electrical energy are called fuel cells.

One of the most successful fuel cells uses the reaction of hydrogen with oxygen to form water as shown in figure. In the cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous sodium hydroxide solution.

Catalysts like finely divided platinum or palladium metal are incorporated into the electrodes for increasing the rate of electrode reactions. The electrode reactions are

At Anode: $$2{H_2}(g) + 4O{H^ - }(aq) \to 4{H_2}O(l) + 4{e^ - }$$

At Cathode: $${O_2}(g) + 2{H_2}O(l) + 4{e^ - } \to 4O{H^ - }(aq)$$

Overall Reaction: $$2{H_2}(g) + {O_2}(g) \to 2{H_2}O(l)$$