What is a hydrogen fuel cell?
A hydrogen fuel cell is a device that produces electricity directly from the reaction between hydrogen and oxygen. Unlike a battery, it does not store its own chemicals; instead, hydrogen fuel and oxygen (from the air) are supplied continuously, so the cell keeps working as long as the reactants flow in. The only chemical product is water, which is why fuel cells are described as a clean source of energy.
Key idea
Overall reaction: 2H2 + O2 → 2H2O. Chemical energy is converted directly into electrical energy.
What happens at the electrodes
Hydrogen is fed to the negative electrode, where it is oxidised (it loses electrons). Oxygen is fed to the positive electrode, where it is reduced (it gains electrons). The electrons flow through the external circuit, and this flow is the electric current.
- Negative electrode (oxidation): 2H2 → 4H+ + 4e−
- Positive electrode (reduction): O2 + 4H+ + 4e− → 2H2O
Worked example
Adding the two half-equations, the 4H+ and 4e− cancel from both sides, leaving 2H2 + O2 → 2H2O. This confirms water is the only product and no carbon dioxide is released.
Advantages and disadvantages
Fuel cells are more efficient than a petrol engine and produce no carbon dioxide or smoke at the point of use. However, hydrogen is difficult and expensive to store safely because it is very flammable, and the hydrogen must first be manufactured, often using energy from fossil fuels.
Remember
- Reactants: hydrogen and oxygen; product: water only.
- Hydrogen is oxidised; oxygen is reduced.
- Chemical energy → electrical energy, with no combustion.