Fuel cells

Fuel cells work in a different way than chemical cells. Fuel cells produce a voltage continuously, as long as they are supplied with:

  • a constant supply of a suitable fuel
  • oxygen, eg from the air

The fuel is oxidised electrochemically, rather than being burned, so the reaction takes place at a lower temperature than if it was to be burned. Energy is released as electrical energy, not thermal energy (heat).

Hydrogen-oxygen fuel cells

Hydrogen-oxygen fuel cells are an alternative to rechargeable cells and batteries. In a hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a voltage. Water is the only product. The overall reaction in a hydrogen-oxygen fuel cell is:

hydrogen + oxygen → water

2H2(g) + O2(g) → 2H2O(l)

Electrode half equations - Higher

At the negative electrode: 2H2 + 4OH- → 4H2O + 4e-

At the positive electrode: O2 + 2H2O + 4e- → 4OH-

When you add these two half equations together, you get the following overall equation:

2H2 + 4OH- + O2 + 2H2O + 4e- → 4H2O + 4e- + 4OH-

The hydroxide ions, electrons and two H2O molecules will now cancel because they are on both sides, leaving the overall equation:

2H2 + O2 → 2H2O