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 + 4e^– → 2O^2– 

• 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 becoming more common in the automotive industry to replace petrol or diesel engines

Advantages

• Hydrogen can be produced from water so the process is renewable

• They do not produce any pollution: the only product is water whereas petrol engines produce carbon dioxide, and oxides of nitrogen

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

• No power is lost in transmission as there are no moving parts, unlike an internal combustion engine

• Quieter so less noise pollution compared to a petrol engine

Disadvantages

• Hydrogen obtained by methods that involve:

  • The combustion of fossil fuels releases carbon dioxide and other pollutants into the atmosphere

  • The electrolysis of water requires large amounts of electricity to produce

• Materials used in producing fuel cells are expensive

• Hydrogen is more difficult and expensive to store compared to petrol as it is very flammable and easily explodes when under pressure 

• Fuel cells are affected by low temperatures, becoming less efficient

• There are only a small number of hydrogen filling stations across the country