A level Chemistry · Edexcel 9CH0 · Topic 14B
Storage and fuel cells
Key points
- Storage (rechargeable) cells reverse their reactions when a current is applied; examples include lithium-ion and lead–acid cells.
- Cell voltage comes from the difference between two electrode potentials; non-rechargeable cells cannot easily be reversed.
- A hydrogen–oxygen fuel cell produces electricity from a continuous supply of fuel and oxygen; overall 2H₂ + O₂ → 2H₂O.
- In alkaline fuel cells: H₂ + 2OH⁻ → 2H₂O + 2e⁻ at the negative electrode and O₂ + 2H₂O + 4e⁻ → 4OH⁻ at the positive electrode.
- Fuel cells can also run on alcohols such as methanol or ethanol.
- Advantages: only water produced, efficient. Disadvantages: hydrogen is flammable and hard to store, and is often made using fossil fuels.
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Batteries and fuel cells are electrochemical cells put to work. Their voltage comes from the same electrode potentials as in 14A; what differs is how the reactants are supplied and whether the reactions can be reversed.
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