GCSE Chemistry revision

Fuel cells

Chemical cells and fuel cells (chemistry only)

AQA 4.5.2.2 Includes HT-only content

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A fuel cell is an electrochemical cell that converts the chemical energy of a fuel and oxygen directly into electrical energy.
The most common type is the hydrogen-oxygen fuel cell, which combines hydrogen and oxygen to produce water whilst generating electrical energy.

The electrolyte sits at the centre of the cell and allows ions to move through it; a common example is potassium hydroxide solution.
The negative anode is on the left and the positive cathode is on the right, connected by a wire that allows electrons to flow between them.
Both electrodes are made of porous carbon, which contains tiny holes and a catalyst to speed up the reaction.
Hydrogen enters the anode compartment on the left, oxygen enters the cathode compartment on the right, and water exits via the outlet of the cathode compartment.

2. Structure of the Hydrogen-Oxygen Fuel Cell AQA

The electrolyte sits at the centre of the cell and allows ions to move through it; a common example is potassium hydroxide solution.
The negative anode is on the left and the positive cathode is on the right, connected by a wire that allows electrons to flow between them.
Both electrodes are made of porous carbon, which contains tiny holes and a catalyst to speed up the reaction.
Hydrogen enters the anode compartment on the left, oxygen enters the cathode compartment on the right, and water exits via the outlet of the cathode compartment.

In a fuel cell, the cathode is positive and the anode is negative, which is the opposite arrangement to electrolysis where the cathode is negative and the anode is positive.

Hydrogen entering the anode compartment is oxidised, meaning each hydrogen atom loses an electron to become a hydrogen ion (H⁺).
The half equation at the anode is: H₂ → 2H⁺ + 2e⁻
The electrons released travel around the external wire to the cathode, whilst the hydrogen ions move through the electrolyte towards the cathode.

4. What Happens at the Anode AQA

Hydrogen entering the anode compartment is oxidised, meaning each hydrogen atom loses an electron to become a hydrogen ion (H⁺).
The half equation at the anode is: H₂ → 2H⁺ + 2e⁻
The electrons released travel around the external wire to the cathode, whilst the hydrogen ions move through the electrolyte towards the cathode.

Combining the two half equations gives the overall equation: 2H₂ + O₂ →2H₂O
The electrical energy is generated by the movement of electrons through the external wire, which can power any electrical device.
In exams, the key point is that as hydrogen fuel enters the cell it is oxidised, setting up a potential difference across the cell that drives electrons around the circuit to generate electricity.

5. What Happens at the Cathode AQA

Combining the two half equations gives the overall equation: 2H₂ + O₂ →2H₂O
The electrical energy is generated by the movement of electrons through the external wire, which can power any electrical device.
In exams, the key point is that as hydrogen fuel enters the cell it is oxidised, setting up a potential difference across the cell that drives electrons around the circuit to generate electricity.

Hydrogen and oxygen are both abundant, meaning fuel cells do not rely on scarce resources.
Fuel cells produce only water as a waste product, so they release no carbon dioxide or other harmful pollutants.
Fuel cells are relatively simple devices, meaning they last longer than conventional batteries and are less polluting to dispose of.

6. Advantages of Hydrogen-Oxygen Fuel Cells AQA

Hydrogen and oxygen are both abundant, meaning fuel cells do not rely on scarce resources.
Fuel cells produce only water as a waste product, so they release no carbon dioxide or other harmful pollutants.
Fuel cells are relatively simple devices, meaning they last longer than conventional batteries and are less polluting to dispose of.

Hydrogen is a gas, so it takes up significantly more space to store compared to liquid fossil fuels or batteries.
Hydrogen is explosive when mixed with air, making its storage potentially dangerous.
Producing the hydrogen fuel in the first place requires energy, which often comes from burning fossil fuels, reducing the overall environmental benefit.

7. Disadvantages of Hydrogen-Oxygen Fuel Cells AQA

Hydrogen is a gas, so it takes up significantly more space to store compared to liquid fossil fuels or batteries.
Hydrogen is explosive when mixed with air, making its storage potentially dangerous.
Producing the hydrogen fuel in the first place requires energy, which often comes from burning fossil fuels, reducing the overall environmental benefit.