Chemical cells and fuel cells (chemistry only)

Cells & Batteries (Triple only)

How chemical cells work

  • Two different metals dipped in an electrolyte.

  • Metals have different reactivities → different tendencies to lose electrons → forms a potential difference (voltage).

  • Bigger difference in reactivity = bigger voltage.

Non-rechargeable cells

  • Reaction only goes one way.

  • Chemicals eventually run out.

Rechargeable batteries

  • Reaction can be reversed using an external electrical current.

  • E.g., lithium-ion batteries.

Fuel cells (Triple only)

Especially hydrogen fuel cells.

5. Hydrogen Fuel Cells (Triple Chemistry)

How they work

  • Hydrogen gas is oxidised to produce electricity.

At the anode:

Hydrogen loses electrons → 2H₂ → 4H⁺ + 4e⁻

At the cathode:

Oxygen reacts with electrons & H⁺ → O₂ + 4H⁺ + 4e⁻ → 2H₂O

Overall reaction:

2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O2H2​+O2​→2H2​O

Advantages

  • Only product: water → no CO₂ emissions.

  • Continuous supply as long as hydrogen is provided.

  • Lightweight.

Disadvantages

  • Hydrogen is hard to store (very flammable).

  • Often made by electrolysis, which requires energy.

  • Expensive catalysts (e.g., platinum).