Fuel Cells (Triple Only)

1. What is a fuel cell?
A fuel cell is a device that converts chemical energy directly into electrical energy. Unlike a normal cell (which eventually runs out of reactants), a fuel cell works continuously, as long as it is supplied with:

• a fuel (such as hydrogen), and
• oxygen (from air)

This produces a voltage that can power external devices (e.g. a motor in a car).

Key idea
Fuel cells are not recharged. They keep producing electricity as long as fuel and oxygen are supplied.

1. Hydrogen goes to the negative electrode (anode)
2. Hydrogen loses electrons, forming H⁺ ions
3. The electrons travel through the external circuit, making electricity
4. At the cathode, oxygen gains electrons
5. H⁺ ions (from the electrolyte) and oxygen combine to make water
6. The only product is H₂O (no CO₂ released)

The electrolyte is often an alkaline solution, such as potassium hydroxide, which allows ions to move.

At the anode (oxidation):
H₂ → 2H⁺ + 2e⁻
At the cathode (reduction):
O₂ + 4H⁺ + 4e⁻ → 2H₂O
Overall reaction:
2H₂ + O₂ → 2H₂O

Because hydrogen is oxidised, it must be at the anode. Oxygen is reduced at the cathode.

Recall