In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to
- remove adsorbed oxygen from electrode surface
- produce high purity water
- generate heat
- create potential difference between the two electrodes
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: 2H2(g) + 4OH–(aq) → 4H2O(l) + 4e–
At cathode: O2(g) + 2H2O(l) + 4e– → 4OH–(aq)
2H2(g) + O2(g) → 2H2O(l)
The correct option is D.