Question

In a hydrogenoxygen fuel cell, combustion of hydrogen occurs to
(a) generate heat
(b) create potential difference between the two electrodes
(c) produce high purity water
(d) remove adsorbed oxygen from electrode surface.

Answer 1

(b) : Direct conversion of chemical energy to electric energy can be made considerably more efficient (i.e. upto 75%) than the 40% maximum now obtainable through burning of fuel and using the heat to form steam for driving turbines. Furthermore, the water obtained as a byproduct may be used for drinking by the astronauts. 

At anode : 2H_2(g) + 4OH^–_(aq) → 4H₂O_(l) + 4e^– 

At cathode : O_2(g) + 2H₂O_(l) + 4e^– → 4OH^–_(aq) 

2H_2(g) + O_2(g) → 2H₂O_(l)