Hydrogen–oxygen fuel cells
How a fuel cell produces electricity from hydrogen and oxygen, and its advantages and disadvantages.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 4.2.1Describe the hydrogen–oxygen fuel cell and evaluate its advantages and disadvantages compared with petrol engines.
5 minute read
Hydrogen–oxygen fuel cells
A hydrogen–oxygen fuel cell generates electricity directly from a chemical reaction between hydrogen and oxygen, without burning either gas.
Hydrogen is supplied at one electrode and oxygen at the other. Inside the cell, hydrogen is oxidised and oxygen is reduced, and the overall reaction is:
2H₂ + O₂ → 2H₂O
The only product is water — there is no combustion, and no carbon-based waste gases are formed, unlike a petrol engine burning a hydrocarbon fuel.
Comparing fuel cells with petrol engines
Advantages of fuel cells: the only product is water, so there is no carbon dioxide or other polluting gas released at the point of use; fuel cells can be more energy-efficient than an internal combustion engine.
Disadvantages of fuel cells: hydrogen gas is difficult and costly to store and transport safely (it is highly flammable and needs high-pressure tanks); there is currently limited infrastructure for refuelling with hydrogen; and producing hydrogen in the first place often uses energy generated from fossil fuels, so the overall environmental benefit depends on how the hydrogen was made.
Think of it like this
A fuel cell is like a battery that never needs recharging, as long as you keep feeding it hydrogen and oxygen — the chemical reaction happens continuously inside, generating electricity directly, rather than through the noisy, wasteful combustion of a petrol engine.
Common misconceptions
- Thinking a fuel cell burns hydrogen like a petrol engine burns fuel. It generates electricity through a controlled chemical reaction, without combustion.
- Assuming hydrogen fuel cells are automatically "zero pollution" overall. The cell itself only produces water, but if the hydrogen used was made using energy from fossil fuels, there is pollution earlier in the process.
- Believing fuel cells have no drawbacks because their only product is water. Storage, transport and infrastructure remain real practical disadvantages.
In the exam
- A balanced evaluation question expects a genuine advantage AND a genuine disadvantage — do not just restate "no pollution" in different words for both marks.
- State the overall equation, 2H₂ + O₂ → 2H₂O, if asked to summarise how the cell works.