Describe how a hydrogen-oxygen fuel cell produces electrical energy, including what happens at each electrode and what is produced overall.

Cambridge International IGCSE Chemistry (0620) — 4.2 Hydrogen-oxygen fuel cells · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Hydrogen gas is supplied to the negative electrode (anode) where it is oxidised:
1. H₂ → 2H⁺ + 2e⁻
The electrons travel through the external circuit to the positive electrode (cathode). At the cathode oxygen is reduced:
2. O₂ + 4H⁺ + 4e⁻ → 2H₂O
The flow of electrons through the circuit constitutes the electric current. Overall the reaction is:
2H₂ + O₂ → 2H₂O
The only product is water.

Examiner tips

  • Use the exact terms ‘anode’, ‘cathode’, ‘oxidised’, ‘reduced’, and ‘electrons flow through the external circuit’.
  • Show the half‑reactions to demonstrate the electron transfer.
  • State that water is the sole product to cover the overall reaction.

Common mistakes

  • Confusing the anode and cathode, e.g. saying oxygen is oxidised.
  • Omitting the electron flow or the external circuit.

Mark scheme (4 marks)

  1. Hydrogen is supplied to / oxidised at the negative electrode (anode)
  2. Oxygen is supplied to / reduced at the positive electrode (cathode)
  3. Electrons flow through the external circuit, producing an electric current
  4. Water is the only product / overall product

Key terms in this question

fuel cell · electrode

Related

More Hydrogen-oxygen fuel cells questions

▶ Try answering this question with AI marking (free) →