Hydrogen Fuel CellsOxford AQA IGCSE Chemistry: Revision notes
Section 1
What is a fuel cell?
A fuel cell produces electricity through a chemical reaction between a fuel and oxygen, without needing to be recharged like a battery — it keeps producing electricity as long as fuel and oxygen are supplied.
Section 2
How does a hydrogen-oxygen fuel cell work?
A hydrogen-oxygen fuel cell uses hydrogen as the fuel, which reacts with oxygen. The only waste product is water:
- Hydrogen and oxygen are supplied continuously to the cell
- They react to produce electricity and water, with no other waste products
- This makes hydrogen fuel cells attractive for reducing air pollution compared with burning fossil fuels
State clearly that water is the ONLY waste product — this is the key exam point that distinguishes fuel cells from combustion engines.
Section 3
How do hydrogen fuel cells compare with hydrogen combustion?
Hydrogen can be used as a fuel in two ways: burning it directly (combustion) or using it in a fuel cell.
| Feature | Hydrogen combustion | Hydrogen fuel cell |
|---|---|---|
| Products | Water (plus oxides of nitrogen from air at high temperature) | Water only |
| Energy conversion | Chemical → heat → (often) mechanical, with losses | Chemical → electrical directly, more efficient |
| Air pollution | Can produce nitrogen oxides | None from the reaction itself |
A hydrogen-powered car with a fuel cell converts chemical energy to electricity to drive an electric motor, whereas a hydrogen combustion engine burns hydrogen like petrol to drive pistons.
Section 4
What are the advantages and disadvantages of hydrogen fuel?
Advantages:
- Produces only water when used in a fuel cell — very low pollution
- Hydrogen can be produced from renewable sources (e.g. electrolysis of water using renewable electricity)
Disadvantages:
- Hydrogen gas is difficult and expensive to store — it needs high-pressure tanks or very low temperatures, and takes up a large volume compared with liquid fuels
- Hydrogen is highly flammable, raising safety concerns
- There is currently limited hydrogen refuelling infrastructure
- Producing hydrogen (e.g. from natural gas or by electrolysis) may itself use energy from non-renewable sources, reducing the overall environmental benefit
Don't claim hydrogen fuel cells have 'zero' environmental impact overall — the hydrogen itself must be produced and stored, and that process may use energy from fossil fuels.
Must Know
- A fuel cell produces electricity from the reaction of a fuel with oxygen
- A hydrogen-oxygen fuel cell produces electricity and water only — no other waste products
- Fuel cells convert chemical energy directly to electrical energy, more efficiently than burning a fuel
- Advantages of hydrogen fuel: low pollution, can be made from renewable sources
- Disadvantages: difficult/expensive to store, highly flammable, limited infrastructure
- Hydrogen combustion can still produce nitrogen oxides at high temperature, unlike a fuel cell
That's the notes covered.
Carry on to the next subtopic.