Question

A hydrogen-oxygen fuel cell is used in the space program to generate clean energy. Describe, in detail, the principle and process of electrical energy generation from hydrogen-oxygen fuel cell. Also include in the discussion major advantages and limitations of such fuel cells.

Answer 1

One of the most succesful fuel cells uses the reaction of hydrogen gas with oxygen gas to form water. The cell was used for providing electrical power in the Appollo space programme. The water vapours produced during the reaction waer condensed and added to the drinking water supply for the astronauts. In the cell, hydrogen and oxygen are bubbled through porous carbon electrodes placed in concentrated aqueous sodium hydroxide solution. Catalysts like finely divided platinumor palladium is incarporated ito the electrodes for increasing the rate of electrode reactions. The electrode reactions are given as,

Cathode: O2 (g) + 2 H2O (l) + 4 e ---------------> 4 OH- (aq.)

Anode: 2 H2 (g) + 4 OH- (aq.) ----------------> 4 H2O (l) + 4 e

Overall reaction: 2 H2 (g) + O2 (g) --------------> 2 H2O (l)

The cell runs continuously as ong as the reactants are supplied. Fuel cells produce electricity with an efficiency of about 70 % compared to thermal palnts whose efficiency is about 40 %. Fuel cells are pollution free and inview of their future importance, a variety of fuel cells have been fabricated and tried.