AQA GCSE Chemistry Foundation (8462), Foundation tier · Energy changes › Chemical cells and fuel cells
Practise Fuel cells. 3 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Chemistry only (not in Combined Science). A fuel cell produces electricity from a fuel, such as hydrogen, and oxygen that are supplied from outside the cell. You need the overall reaction in a hydrogen fuel cell, and to evaluate hydrogen fuel cells compared with rechargeable cells and batteries.
Key facts
Fuel cell: fuel and oxygen supplied from outside; the fuel is oxidised electrochemically to produce a potential difference
Hydrogen fuel cell overall: 2H2 + O2 → 2H2O
Only product: water
Fuel cell: refuelled. Battery: recharged.
Notes
What a fuel cell is
A fuel cell is supplied with a fuel (e.g. hydrogen) and oxygen or air from an external source.
The fuel is oxidised electrochemically inside the cell to produce a potential difference. The fuel does not burn.
A fuel cell keeps producing electricity for as long as fuel and oxygen are supplied. It is refuelled, not recharged.
The hydrogen fuel cell
diagram
The overall reaction is the oxidation of hydrogen to produce water: 2H2 + O2 → 2H2O
Hydrogen and oxygen go in, water comes out, and electrons flow round the external circuit.
Water is the only product, so the fuel cell releases no carbon dioxide or other pollutants while it is working.
Fuel cells compared with rechargeable batteries
Hydrogen fuel cells are a possible alternative to rechargeable cells and batteries, for example in vehicles.
For fuel cells: they are refuelled in a few minutes and keep working as long as fuel is supplied.
Against fuel cells: hydrogen is a gas, so it takes up a large volume and is stored under high pressure; it is flammable (explosive when mixed with air); there are few filling stations; and it is often made using fossil fuels.
For batteries: they can be recharged from the mains. Against batteries: recharging takes a long time, they can only be recharged a limited number of times, they are difficult to dispose of, and the electricity may come from fossil fuels.
Neither releases carbon dioxide while it is being used, so 'no carbon dioxide' is not a difference between them.
How to answer each type of question
Recall: what goes in and what comes out
1 to 4 marksGrade 4
Inputs: hydrogen and oxygen (or air).
Output: water only (and electricity).
For the balanced equation, check there are 4 H atoms and 2 O atoms on each side.
Example. (a) Name the two substances supplied to a hydrogen fuel cell. (2) (b) Write a balanced symbol equation for the overall reaction in a hydrogen fuel cell. (2)
Saying a fuel cell burns hydrogen. The hydrogen is oxidised electrochemically; there is no combustion.
Saying hydrogen fuel cells produce 'no waste' or 'nothing'. They produce water.
Saying hydrogen fuel cells cause no pollution at all. Making the hydrogen, or the electricity used to make it, often uses fossil fuels.
Giving 'no carbon dioxide' as an advantage over batteries. Battery vehicles release no carbon dioxide while in use either.
More tips
Memory tricks
Fuel cell = refuel; battery = recharge.
The overall equation is the same as for burning hydrogen, but in a fuel cell there is no flame: the reaction produces a potential difference.
Exam technique
In 'evaluate' questions, check what the fuel cell is compared with. 'Only water is produced' is a strong point against petrol engines, not against batteries.
Use numbers from the table for both sides, add your own knowledge, and finish with a conclusion that follows from your points.
Use the key phrase: the fuel is 'oxidised electrochemically' to produce a potential difference.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Name what a hydrogen fuel cell usesHydrogen (the fuel) and oxygen or air are supplied to the cell from outside.
Grade 4
State the product of a hydrogen fuel cellThe only product is water: 2H2 + O2 → 2H2O.
Grade 5
Describe how fuel cells produce a potential differenceThe fuel is oxidised electrochemically inside the cell, which produces a potential difference.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Name the only product of the reaction in a hydrogen fuel cell.
Water
State one similarity between a hydrogen fuel cell and a rechargeable battery.
Both convert chemical energy into electrical energy using a chemical reaction.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Hydrogen fuel cells can be used to power vehicles.
(a) Which two substances are supplied to a hydrogen fuel cell? Tick (✓) two boxes.[2]
Carbon dioxide
Hydrogen
Nitrogen
Oxygen or air
Water
(b) Name the only product of the reaction in a hydrogen fuel cell.[1]
(c) Is hydrogen oxidised or reduced in the fuel cell?[1]
(d) Give one advantage of a vehicle powered by a hydrogen fuel cell compared with a vehicle powered by a petrol engine.[1]
Show the answer and mark scheme
(a)Answer: Hydrogen; Oxygen or air
(b)Answer: Water
water
(c)Answer: Oxidised
oxidised
(d)Answer: No carbon dioxide is produced when it is used.
no carbon dioxide is produced (while it is being used) / only water is produced / no pollutants such as carbon monoxide are produced
Question 2Medium5 marks
{fig} shows a hydrogen fuel cell.
[object Object]
(a) Write a balanced symbol equation for the overall reaction in a hydrogen fuel cell.[2]
(b) In the fuel cell, hydrogen is oxidised electrochemically. What is oxidation, in terms of electrons?[1]
(c) Give two differences between the way a hydrogen fuel cell and a rechargeable battery provide electricity.[2]
Show the answer and mark scheme
(a)Answer: 2H2 + O2 → 2H2O
correct formulae: H2 + O2 → H2O
balanced: 2H2 + O2 → 2H2O
(b)Answer: Loss of electrons
loss of electrons
(c)Answer: A fuel cell needs a continuous supply of hydrogen and oxygen from outside, whereas a battery stores its chemicals inside; a fuel cell is refuelled, whereas a battery is recharged with an electric current.
a fuel cell needs a continuous supply of fuel and oxygen from outside, but a battery contains all its reactants
a fuel cell is refuelled, but a battery is recharged by supplying an electric current
a fuel cell produces water that leaves the cell, but a battery releases no products
a fuel cell keeps working while fuel is supplied, but a battery stops when a reactant is used up (until it is recharged)