Hydrogen Fuel Cells (Cambridge (CIE) IGCSE Chemistry): Revision Note

Hydrogen fuel cells

• A fuel is a substance which releases energy when burned

• Hydrogen is used as a fuel in rocket engines and in fuel cells to power some cars

• A fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode

  • H₂ → 2H⁺ + 2e^– 

  • O₂ + 4H⁺ + 4e^- → 2H₂O

• The hydrogen-oxygen fuel cell produces electricity by combining both elements, releasing energy and water

• The overall equation for the reaction within a hydrogen fuel cell is:

hydrogen   +   oxygen   →   water

2H₂ + O₂ → 2H₂O

• The diagram below shows the setup of a hydrogen fuel cell 

  • The air entering provides the oxygen

  • The fuel entering is hydrogen

  • The only chemical product made is water 

Diagram showing the movement of hydrogen, oxygen and electrons in a hydrogen-oxygen fuel cell

Advantages & disadvantages of hydrogen fuel cells

Extended tier only

• Hydrogen-oxygen fuel cells are an alternative technology for powering vehicles, replacing traditional petrol or diesel engines.

Advantages

No pollutants produced

• The only product of the reaction is water. This is a major advantage over petrol engines which produce harmful pollutants such as carbon dioxide (a greenhouse gas), oxides of nitrogen (which cause acid rain), and carbon monoxide.

High efficiency

• They release more energy per kilogram than either petrol or diesel.

Renewable

• The hydrogen fuel can be produced by the electrolysis of water, which is a renewable resource.

Disadvantages

Hydrogen production:

• Most hydrogen is currently produced from fossil fuels (like methane), which is a non-renewable process that releases carbon dioxide.

• The electrolysis of water requires large amounts of electricity, which may be generated by burning fossil fuels.

Storage and Safety

• Hydrogen is a highly flammable gas that is difficult and expensive to store safely, often requiring high-pressure tanks. This is less convenient than storing liquid petrol.

Cost and Infrastructure:

• The materials used to make fuel cells are often expensive.

• There is a very limited number of hydrogen filling stations available.