4.2 Hydrogen–oxygen fuel cells
- Syllabus
- 0620–2026–2027
- Topic
- 4.2
- Level
- —
Learning objectives
4.2.1Hydrogen–oxygen fuel cell uses• State: a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product4.2.2Advantages and disadvantages of using• Describe advantages and disadvantages of using hydrogen–oxygen fuel cells in comparison with gasoline/petrol engines in vehicles
Explain a hydrogen–oxygen fuel cell
A hydrogen–oxygen fuel cell uses a continuous supply of hydrogen and oxygen to produce electricity. Water is the only chemical product.
The overall reaction is 2H₂ + O₂ → 2H₂O. Chemical energy is converted directly into electrical energy that can power an electric motor.
The cell consumes hydrogen; it does not manufacture hydrogen. The reaction is exothermic, and carbon dioxide is not a direct product of the cell.
Compare fuel-cell and petrol vehicles
| Factor | Hydrogen–oxygen fuel cell | Petrol engine |
|---|---|---|
| product at vehicle | water; no direct CO₂ or toxic exhaust gases | CO₂ and other combustion pollutants may form |
| energy conversion | can be more efficient | substantial energy lost as heat |
| fuel storage | hydrogen is difficult to store, needs high pressure or large volume, and can leak | petrol is easier to store and has established infrastructure |
| supply and cost | hydrogen production, transport and catalysts can be costly | mature fuel supply network |
A fair comparison includes the full energy source: producing hydrogen may use fossil fuels or electricity, so low vehicle emissions do not automatically mean zero total environmental impact.
Water as the only chemical product describes the operating fuel cell, not every upstream process used to make and deliver hydrogen.