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A fuel cell is an electrochemical device that converts chemical energy from a fuel and oxygen directly into electrical energy. 8 questions answered.
Introduction to Fuel Cells is part of Chemical cells and fuel cells (chemistry only) in GCSE AQA Higher Chemistry.
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A fuel cell is an electrochemical device that converts chemical energy from a fuel and oxygen directly into electrical energy. 8 questions answered.
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Use this lesson to stay inside Chemical cells and fuel cells (chemistry only) while connecting the detail back to the wider Topic 5: Energy changes topic.
Read the core explanations from Introduction to Fuel Cells before testing yourself from memory.
Your phone battery runs down and needs recharging. But what if you had a battery that could run forever, as long as you kept feeding it fuel? That's exactly what a fuel cell does.
Unlike normal batteries that store energy inside them, fuel cells are supplied by an external source of fuel (like hydrogen) and oxygen from the air. Think of it like the difference between a torch with built-in batteries versus one you plug into the mains.
The key difference is that the fuel is oxidised electrochemically within the fuel cell to produce a potential difference. This means the chemical reaction happens in a controlled way that generates electricity directly, rather than just producing heat like burning.
The most common type of fuel cell uses hydrogen as fuel. Here's what happens inside: hydrogen gas enters at one electrode (the anode), while oxygen from air enters at the other electrode (the cathode).
At the anode, hydrogen molecules are split into hydrogen ions (H⁺) and electrons. The electrons flow through an external circuit, creating the electric current we want. Meanwhile, the hydrogen ions travel through an electrolyte to the cathode.
At the cathode, oxygen combines with the hydrogen ions and electrons to form water. This is the overall reaction in a hydrogen fuel cell: the oxidation of hydrogen to produce water.
Worked example: The Complete Hydrogen Fuel Cell Reaction
Show the overall reaction when hydrogen fuel reacts with oxygen in a fuel cell.
Answer: $2H_2 + O_2 \rightarrow 2H_2O$ (plus electrical energy)
Notice that the only waste product is water - completely clean! This is why hydrogen fuel cells are considered environmentally friendly, unlike burning fossil fuels which produces carbon dioxide.
Hydrogen fuel cells offer a potential alternative to rechargeable cells and batteries. But like any technology, they have both advantages and disadvantages compared to what we use now.
The biggest advantage is that fuel cells can run continuously as long as you supply fuel and oxygen. A rechargeable battery eventually runs down and needs hours to recharge. A fuel cell just needs more hydrogen - you can 'refuel' it in minutes, just like filling up a car with petrol.
Fuel cells can be efficient because they convert chemical energy directly to electrical energy.
However, there are challenges. Hydrogen is difficult to store safely - it's a very light gas that can leak easily and is highly flammable. The infrastructure for hydrogen refuelling stations barely exists compared to petrol stations or electrical charging points.
Fuel cells aren't just laboratory curiosities - they're already being used in several important applications. Fuel cells are used in some transport and power applications.
Hydrogen fuel cell vehicles can be refuelled quickly and are being developed for transport use.
Fuel cells are also used or tested for some stationary power applications.
Exam questions on fuel cells often test whether you understand the key differences from normal batteries. Remember that fuel cells need continuous external supply of fuel and oxygen, while batteries store energy internally.
When describing how fuel cells work, examiners want you to mention that the fuel is 'oxidised electrochemically' - this shows you understand it's a controlled chemical reaction that produces electricity directly, not just burning.
For hydrogen fuel cells specifically, always state that the overall reaction is hydrogen + oxygen → water. Don't forget that this produces electrical energy as well as water.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-19.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
A fuel cell is an electrochemical device that converts chemical energy from a fuel and oxygen directly into electrical energy. The fuel, such as hydrogen, is supplied externally and oxidised electrochemically within the cell to produce a potential difference.
The overall reaction in a hydrogen fuel cell is 2H₂ + O₂ → 2H₂O, the oxidation of hydrogen to produce water and electrical energy. Water is the only waste product.
The disadvantages of hydrogen fuel cells are that hydrogen is difficult to store safely, because it is a very light gas that leaks easily and is highly flammable, and that there are very few hydrogen refuelling stations compared with petrol stations or charging points.
Fuel cells are used in some transport and power applications. Hydrogen fuel cell vehicles can be refuelled quickly and are being developed for transport use, and fuel cells are also used or tested for some stationary power applications.
Hydrogen is difficult to store safely because it is a very light gas that can leak easily and is highly flammable. This, along with the lack of hydrogen refuelling stations, is a major challenge for hydrogen fuel cells.
Hydrogen fuel cells are considered environmentally friendly because the only waste product is water, unlike burning fossil fuels, which produces carbon dioxide. They also convert chemical energy directly into electrical energy rather than just producing heat.
In a hydrogen fuel cell, the electrolyte lets hydrogen ions (H⁺) travel from the anode to the cathode. At the anode hydrogen splits into H⁺ ions and electrons; the electrons flow through the external circuit while the ions cross the electrolyte to combine with oxygen and form water.
In a fuel cell, hydrogen is oxidised electrochemically, a controlled reaction that produces a potential difference and generates electricity directly. Burning hydrogen just produces heat, even though both give water as the product.