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9.3.2Metals

Hydrogen Fuel Cells — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 8 of 8 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 4How a Hydrogen Fuel Cell Works

9.3.2 Hydrogen Fuel Cells

A fuel cell produces electricity from a fuel reacting with oxygen, without burning it.

1
A hydrogen-oxygen fuel cell generates electricity from the reaction of hydrogen with oxygen.
2
Hydrogen is oxidised at the negative electrode, and oxygen is reduced at the positive electrode.
3
The overall reaction is 2H₂ + O₂ → 2H₂O, and it is exothermic.
4
Electrons travel through the external circuit from the hydrogen electrode to the oxygen electrode, providing the electric current.

Part 2 of 4Advantages and Disadvantages

Hydrogen is a promising fuel, but its production and storage have drawbacks.

Renewable
  • Hydrogen can be made from water, so the fuel supply is renewable when the electricity used is renewable.
Clean product
  • Burning hydrogen gives only water, so it does not add carbon dioxide or acid-forming gases to the air.
Production
  • Making hydrogen by electrolysis of water needs large amounts of electricity.
Storage and safety
  • Hydrogen must be stored in bulky pressurised containers, and it forms an explosive mixture with air.

Part 3 of 4Equations and Uses

Both word and symbol equations must be known for the fuel cell reaction.

Equations and Uses
Word equation
  • Hydrogen + oxygen → water is the word equation for the overall fuel cell reaction.
Symbol equation
  • 2H₂ + O₂ → 2H₂O, with four hydrogen atoms and two oxygen atoms on each side.
Uses
  • Hydrogen fuel cells are used to power spacecraft and some cars.
Energy
  • The reaction releases energy as electricity and heat, which is why the overall reaction is exothermic.

Part 4 of 4Exam Checklist & Tips

9.3.2 – Key Points for the Exam

  • Fuel cell A device that converts the chemical energy of a fuel and oxygen directly into electrical energy.
  • Electrolysis The use of electricity to break down a compound, such as water, into elements.
  • Renewable energy source A source that is replaced naturally and does not run out.
  • Explosive mixture A mixture, such as hydrogen and air, that can ignite and explode.

Common Mistakes

  • Writing the fuel cell equation without balancing it, such as H₂ + O₂ → H₂O.
  • Saying that a hydrogen fuel cell produces carbon dioxide; its only product is water.
  • Claiming hydrogen is always renewable;
    • it is only renewable when the electricity used to make it comes from renewable sources.
  • Forgetting that the fuel cell reaction is exothermic when describing its energy change.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

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