Identify incorrect statement about \(H_2-O_2\) fuel cell from the following:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The cell runs continuously even if reactants are not supplied
A fuel cell converts the energy of combustion of a fuel directly into electrical energy. In the \( \ce{H2-O2} \) fuel cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous NaOH:
Cathode: \( \ce{O2(g) + 2H2O(l) + 4e- -> 4OH^-(aq)} \)
Anode: \( \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e-} \)
Net reaction: \( \ce{2H2(g) + O2(g) -> 2H2O(l)} \)
Option (1) At cathode O2 is reduced to OH− — A correct statement about the fuel cell. \( \ce{O2} \) gains electrons at the cathode and forms \( \ce{OH-} \) ions.
Option (2) At anode H2 is oxidised to form water — A correct statement about the fuel cell. \( \ce{H2} \) loses electrons and combines with \( \ce{OH-} \) to give water.
Option (3) The cell runs continuously even if reactants are not supplied — The incorrect statement. The reactants are used up at the electrodes, so the cell runs only as long as the reactants are supplied.
Option (4) Water is formed as a by product — A correct statement about the fuel cell. Water is the only product; in the Apollo space programme it was added to the astronauts’ drinking water.
NCERT (2026-27 edition):
Fuel Cells – “… In the cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous sodium hydroxide solution. … The cell runs continuously as long as the reactants are supplied.”