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Cambridge IGCSE Chemistry · 0620
Chapter 4: Electrochemistry — Part 3
Topic 4.2 · Hydrogen–oxygen fuel cells
Basic Principles
Hydrogen-oxygen fuel cells are used as an alternative to chemical cells to produce electricity. They use hydrogen and oxygen to generate a voltage, with water as the only chemical product.
The Chemical Reaction
The overall reaction in the fuel cell is:
Hydrogen + Oxygen ? Water
2H2(g) + O2(g) ? 2H2O(l)
Exam Traps
- Do not write H2 + O2 → H2O without balancing — two water molecules form per two hydrogen molecules.
- Do not confuse fuel cells with electrolysis of water, which splits water using electricity.
Comparison with Gasoline/Petrol Engines
Fuel cells are increasingly used in vehicles as a cleaner alternative to traditional internal combustion engines.
| Advantages | Disadvantages |
|---|---|
| Produces less carbon dioxide emissions because water is the only product. | Expensive to produce and requires costly transport of hydrogen. |
| Reduces the use of fossil fuels. | Less durable and not as long-lasting as gasoline engines. |
Exam Traps
- Do not claim fuel cells produce zero pollution overall — hydrogen production and transport may use fossil fuels.
- Do not say fuel cells are more durable than petrol engines — the syllabus lists shorter lifespan as a disadvantage.
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