Hydrogen-oxygen fuel cells
Cambridge IGCSE Chemistry (0620) · Unit 4: Electrochemistry · 8 flashcards
Hydrogen-oxygen fuel cells is topic 4.3 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 4 — Electrochemistry , alongside Electrolysis and Electrolysis of specific substances. In one line: A hydrogen-oxygen fuel cell is an electrochemical device that converts chemical energy from hydrogen and oxygen directly into electrical energy. Water is the only chemical product formed.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). It is a Supplement (Extended-tier) topic, so it appears only on the Extended-tier papers. Past papers from 2022 to 2025 show this topic across undefined questions worth 134 marks (around 2.1% of all Chemistry marks in those years).
The deck below contains 8 flashcards — 1 definition, 6 key concepts and 1 study tip — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
Watch out: one common mark-loser flagged on this topic — read the study-tip card below before attempting past-paper questions.
A hydrogen-oxygen fuel cell
A hydrogen-oxygen fuel cell is an electrochemical device that converts chemical energy from hydrogen and oxygen directly into electrical energy. Water is the only chemical product formed.
Questions this Hydrogen-oxygen fuel cells deck will help you answer
- › What are the reactants and products in a hydrogen-oxygen fuel cell?
- › State two advantages of hydrogen-oxygen fuel cells compared to petrol engines.
- › State two disadvantages of hydrogen-oxygen fuel cells.
- › Why is a hydrogen-oxygen fuel cell considered better for the environment than burning petrol?
- › How does a hydrogen-oxygen fuel cell differ from a battery?
Common mark-losers in Hydrogen-oxygen fuel cells
Why might the production of hydrogen for fuel cells still cause environmental problems?
Most hydrogen is currently produced by steam reforming of natural gas (methane), which releases CO₂:
CH₄ + H₂O → CO + 3H₂
Only hydrogen produced by electrolysis of water using renewable electricity is truly carbon-free. The source of the hydrogen determines whether the overall process is environmentally friendly.
What is a hydrogen-oxygen fuel cell?
A hydrogen-oxygen fuel cell is an electrochemical device that converts chemical energy from hydrogen and oxygen directly into electrical energy. Water is the only chemical product formed.
What are the reactants and products in a hydrogen-oxygen fuel cell?
Reactants: hydrogen (H₂) and oxygen (O₂).
Product: water (H₂O).
The overall reaction is: 2H₂ + O₂ → 2H₂O
Electrical energy is released during this reaction rather than heat.
State two advantages of hydrogen-oxygen fuel cells compared to petrol engines.
1. The only product is water, so fuel cells produce no pollutants such as carbon dioxide, carbon monoxide, nitrogen oxides, or sulfur dioxide.
2. Fuel cells are more energy-efficient than combustion engines because they convert chemical energy directly to electrical energy without the energy losses from burning fuel.
State two disadvantages of hydrogen-oxygen fuel cells.
1. Hydrogen is highly flammable and difficult to store safely — it must be kept as a compressed gas or liquid at very low temperatures.
2. Most hydrogen is currently produced from fossil fuels (
Why is a hydrogen-oxygen fuel cell considered better for the environment than burning petrol?
Burning petrol produces CO₂ (a greenhouse gas contributing to climate change), CO (toxic), NOₓ (causes acid rain and smog), and particulates. A hydrogen fuel cell only produces water. As long as the hydrogen is produced from renewable sources (
How does a hydrogen-oxygen fuel cell differ from a battery?
A battery stores a fixed amount of chemical energy and eventually runs out. A fuel cell continuously produces electricity as long as hydrogen and oxygen are supplied — it does not run out or need recharging. However, it does require a constant supply of fuel (hydrogen).
What type of energy conversion occurs in a hydrogen-oxygen fuel cell?
Chemical energy (stored in the hydrogen and oxygen) is converted directly into electrical energy. This is more efficient than a petrol engine, which converts chemical energy → thermal energy → kinetic energy, losing energy at each stage.
Why might the production of hydrogen for fuel cells still cause environmental problems?
Most hydrogen is currently produced by steam reforming of natural gas (methane), which releases CO₂:
CH₄ + H₂O → CO + 3H₂
Only hydrogen produced by electrolysis of water using renewable electricity is truly carbon-free. The source of the hydrogen determines whether the overall process is environmentally friendly.
Key Questions: Hydrogen-oxygen fuel cells
What is a hydrogen-oxygen fuel cell?
A hydrogen-oxygen fuel cell is an electrochemical device that converts chemical energy from hydrogen and oxygen directly into electrical energy. Water is the only chemical product formed.
Tips to avoid common mistakes in Hydrogen-oxygen fuel cells
- ● When burning a hydrocarbon fuel, remember that both carbon and hydrogen are needed to produce carbon dioxide AND water.
- ● Write the balanced equation for water electrolysis (2H2O → 2H2 + O2) and note the stoichiometric coefficients.
- ● Mnemonic: 'Hydro-*carbons*' only contain hydrogen and carbon.
- ● Sketch a diagram of the hydrogen-oxygen fuel cell; label hydrogen and oxygen as the inputs, and water as the only output.
- ● To nail the hydrocarbon definition, repeat this phrase: 'A compound of carbon and hydrogen ONLY'.
More topics in Unit 4 — Electrochemistry
Hydrogen-oxygen fuel cells sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Hydrogen-oxygen fuel cells deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Chemistry guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
How to study this Hydrogen-oxygen fuel cells deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Space to flip • ←→ to navigate • Esc to close
You're on a roll!
You've viewed 10 topics today
Create a free account to unlock unlimited access to all revision notes, flashcards, and study materials.
You're all set!
Enjoy unlimited access to all study materials.
Something went wrong. Please try again.
What you'll get:
- Unlimited revision notes & flashcards
- Track your study progress
- No spam, just study updates