Question 1

What is a hydrogen–oxygen fuel cell?

Accepted Answer

It is an electrochemical device that converts the chemical energy of hydrogen and oxygen into electrical energy. NCERT describes a hydrogen–oxygen fuel cell with two porous carbon electrodes and concentrated aqueous NaOH between them.

Question 2

What happens at the anode?

Accepted Answer

Hydrogen is oxidised at the anode. In an alkaline electrolyte, the reaction is 2H₂ + 4OH⁻ -> 4H₂O + 4e⁻. The released electrons move into the external circuit.

Question 3

What happens at the cathode?

Accepted Answer

Oxygen is reduced at the cathode according to O₂ + 2H₂O + 4e⁻ -> 4OH⁻. Hydroxide ions formed here move through the electrolyte toward the anode, completing the internal circuit.

Question 4

What is the overall reaction of the fuel cell?

Accepted Answer

Adding the two half-reactions and cancelling common OH⁻, H₂O and electrons gives 2H₂ + O₂ -> 2H₂O. For a hydrogen–oxygen cell, water is the only net chemical product.

Question 5

How is this fuel cell different from a battery?

Accepted Answer

A fuel cell receives hydrogen and oxygen from outside, so it can operate while these reactants are supplied. A battery stores its reactants within the cell. NCERT treats fuel cells separately because the fuel and oxidant are supplied continuously from outside.

Question 6

What changes when PEM is selected?

Accepted Answer

The model shows a proton-exchange membrane and hydrated H⁺ moving from anode to cathode. The PEM reactions are 2H₂ -> 4H⁺ + 4e⁻ at the anode and O₂ + 4H⁺ + 4e⁻ -> 2H₂O at the cathode.

Fuel Cell in 3D — Hydrogen, Oxygen and Water Without Fire

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