How to make a potato battery?
- A potato
- A clean copper coin (If necessary clean it by placing it in a fizzy drink for a few minutes, or clean with steel wool)
- Some aluminium foil
- Crocodile clips
- A voltmeter or multimeter
Cut the potato in half and place the flat end on the foil. Push the copper coin into the potato. Attach crocodile clips to the coin and the foil, then wires to the crocodile clips. Now attach these wires to the voltmeter. The volt meter should give a reading, showing that the stored energy is available and a current can flow, and that you have produced a battery!
Why this happens?
The potato contains a mild phosphoric acid (H3PO4), which acts as the electrolyte.
At the copper coin there are two reactions that could take place. If there is sufficient oxygen present, oxygen ions will be reduced to oxygen gas in the reaction
O2 + 4H+ + 4e– → 2O2– + 2H2O 1.23 V
If there is not sufficient oxygen, hydrogen ions from the acid are reduced to hydrogen gas in the reaction
H+ + e– → ½H2 0 V
At the foil aluminium metal is reduced to aluminium ions in the reaction
Al → Al3+ + 3e– 1.66 V
The total theoretical voltage across the potato cell is therefore 2.89 V in sufficient oxygen (Aluminium/air battery), or 1.66 V in insufficient oxygen (Aluminium/Hydrogen battery).
This also works with lemons, tomatoes, apples and other fruits!