AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Fuel cells are used to generate an electric current and do not need to be…
Full specification wording
Commercial applications of electrochemical cells (A-level only): Fuel cells are used to generate an electric current and do not need to be electrically recharged.
A fuel cell is not a store of energy but a converter.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 2 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A fuel cell is not a store of energy but a converter. Fuel and oxygen are fed in continuously from outside, so the electrode reactions never run down and the cell needs no electrical recharging; it needs refuelling. A hydrogen and oxygen fuel cell converts the chemical energy of the reaction directly into electrical energy, skipping the heat and mechanical stages of an engine, so it reaches a much higher efficiency than burning the same hydrogen. The only product at the point of use is water, so no carbon dioxide, nitrogen oxides or particulates are released in the street. The difficulties are upstream and practical: hydrogen is usually manufactured from methane, so carbon dioxide is released at the plant; it is hard to store and transport safely; and the electrodes need expensive catalysts.
What earns the marks
- Stating that the fuel and the oxygen are supplied continuously from outside the cell.
- Stating that the cell does not need to be electrically recharged because the reactants are supplied continuously.
- Identifying water as the only product at the point of use.
- A named limitation, such as storing or transporting hydrogen, or making hydrogen from a fossil fuel.
Common mistakes and how to put them right
Describing a fuel cell as storing energy in the same way as a battery.
Claiming a hydrogen fuel cell is carbon neutral without considering how the hydrogen was manufactured.
Stating that the fuel cell is 100% efficient.
Saying the cell must be recharged when the electrolyte is used up, when the electrolyte is not consumed.
Exam tips
- 'Does not need recharging' earns the mark only when paired with the reason: the reactants are supplied continuously.
- For any comparison with a petrol engine, name the efficiency advantage and the emission at the point of use separately.
Try the lesson
The start of the Commercial applications of electrochemical cells (A-level only): Fuel cells are used to generate an electric current and do not need to be electrically recharged. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes a key advantage of a hydrogen–oxygen fuel cell compared with a rechargeable lithium-ion battery?
Listen
A fuel cell is not a store of energy but a converter. Fuel and oxygen are fed in continuously from outside, so the electrode reactions never run down and the cell needs no electrical recharging; it needs refuelling. A hydrogen and oxygen fuel cell converts the chemical energy of the reaction directly into electrical energy, skipping the heat and mechanical stages of an engine, so it reaches a much higher efficiency than burning the same hydrogen. The only product at the point of use is water, so no carbon dioxide, nitrogen oxides or particulates are released in the street. The difficulties are upstream and practical: hydrogen is usually manufactured from methane, so carbon dioxide is released at the plant; it is hard to store and transport safely; and the electrodes need expensive catalysts. A strong answer earns marks for these points. stating that the fuel and the oxygen are supplied continuously from outside the cell. stating that the cell does not need to be electrically recharged because the reactants are supplied continuously. identifying water as the only product at the point of use. a named limitation, such as storing or transporting hydrogen, or making hydrogen from a fossil fuel. Exam tip: 'Does not need recharging' earns the mark only when paired with the reason: the reactants are supplied continuously.
Key words
Say what each word means before you turn the card.
fuel cells
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continuous supply of reactants
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water as only product
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See every definition
- fuel cells
- Devices used to generate an electric current that do not need to be electrically recharged.
- continuous supply of reactants
- Fuel and oxygen are fed in continuously from outside, so the electrode reactions never run down and the cell needs refuelling.
- water as only product
- The only product at the point of use is water, so no carbon dioxide, nitrogen oxides or particulates are released in the street.
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