Which of the following is correct about the hydrogen–oxygen fuel cell that was used for providing electrical power in the Apollo space programme?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The water vapours produced during the reaction were condensed and added to the drinking water supply for the astronauts.
A fuel cell is a galvanic cell that turns the energy of combustion of a fuel directly into electrical energy. In the hydrogen–oxygen fuel cell the only product is water:
Cathode: \( \displaystyle \ce{O2(g) + 2H2O(l) + 4e^- -> 4OH^-(aq)} \)
Anode: \( \displaystyle \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \)
Cell reaction: \( \displaystyle \ce{2H2(g) + O2(g) -> 2H2O(l)} \)
In the Apollo space programme this water was condensed and used as drinking water for the astronauts.
Why the other options are incorrect
Option (2) Hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous sulphuric acid. — Incorrect. The gases are bubbled through porous carbon electrodes into concentrated aqueous sodium hydroxide; the electrode reactions above use OH− ions.
Option (3) The cell produces electricity with an efficiency of about 40%, close to that of thermal plants. — Incorrect. Fuel cells work with an efficiency of about 70%; about 40% is the efficiency of thermal plants.
Option (4) Finely divided iron is incorporated into the electrodes as a catalyst for the electrode reactions. — Incorrect. The catalysts in the electrodes are finely divided platinum or palladium.
NCERT (2026-27 edition):
2.7 Fuel Cells – “One of the most successful fuel cells uses the reaction of hydrogen with oxygen to form water… The cell was used for providing electrical power in the Apollo space programme. The water vapours produced during the reaction were condensed and added to the drinking water supply for the astronauts.”