Here you can watch the episode of Take Off where this challenge takes place.

Starting at minute 15:10, you can see how the contestants tackled this challenge.

Goal of the Challenge

The goal of the Potato Battery Challenge is for students to build a battery using potatoes (or other fruits and vegetables) that can generate a voltage of 5 volts. The first team to measure 5 volts with a multimeter wins!

Materials and Preparation

Each group will need the following materials:

• 10 potatoes or potato pieces (or 10 half lemons)
• 10 pieces of copper wire (approximately 10 cm long)
• 9 zinc nails or screws (or other conductive metals like aluminum or iron)
• 10 alligator clips
• 1 multimeter
• 1 piece of sandpaper
• 1 printed circuit diagram (can be downloaded further below)
• Optional: 1 towel for cleaning up
• Optional: Aluminum foil
• Optional: Various fruits and vegetables (e.g., bananas, apples)
• Optional: 200 ml saline solution or cola and 5-10 small cups (e.g., plastic shot glasses)

Preparation

1. Gather the materials.
2. Watch the video above.
3. Decide how best to divide the class into groups and where the groups can be spaced around the room.

Specific Procedure

Question/Challenge:
Explain the challenge and the criteria for winning to the students. Encourage them to ask any questions they might have at this point to ensure they understand everything and the rules are clear for everyone before the challenge begins.

Formulating Hypotheses:
Give the teams a few minutes to discuss possible methods and formulate hypotheses on how they can achieve the goal. Every team member should contribute ideas. This phase prevents the students from diving into the challenge without a plan.

Experiment/Competition:
Now, the competition begins! The students test and optimize their circuits. The first team to measure a voltage of 5 volts with the multimeter wins the challenge.

Conclusion/Explanation:
After the competition, have a group discussion:

• Why was the winning team's battery successful?

• What improvements could be made to the other batteries?

• How does the potato battery work scientifically? What are the similarities and differences compared to traditional batteries? (See the section below for more details.)

Possible Method:

The potato serves as the electrolyte because the acids inside it can transport electrical charges. The zinc nail acts as the anode (negative electrode), and the copper wire serves as the cathode (positive electrode). This creates a small battery with a voltage of about 0.8 volts.

The voltage of the potato batteries is measured using a multimeter. If the voltage is less than 0.8 volts per potato, make sure to:

• Ensure the contact surfaces are clean and large enough.

• Ensure the metals are inserted deep enough into the potatoes.

• Sand the surface of the metals to increase the contact area.

To increase the voltage, the students need to connect multiple potato batteries in series, by linking the zinc nail of one potato to the copper wire of the next potato, and so on, until the desired voltage is reached.

What exactly happens inside the potato? 

In the Episode Joseph explains, starting at minute 16:50, what exactly happens inside the potato and how the electron flow occurs.

How does a conventional battery work?

The potato battery converts chemical energy into electrical energy—just like the classic Daniell cell, which serves as a model for modern batteries. The Daniell cell generates electrical energy through a redox reaction. Two half-reactions take place: Oxidation occurs at the anode, while reduction takes place at the cathode.

Structure of a Daniell Cell:

The Daniell cell consists of two half-cells:

• Anode (Negative pole, zinc electrode in zinc sulfate solution): Zinc releases electrons and becomes zinc ions (Zn²⁺).

• Cathode (Positive pole, copper electrode in copper sulfate solution): Copper ions (Cu²⁺) accept electrons and deposit as metallic copper.

• Electrolyte (Salt bridge or porous membrane): Allows charge balance by transporting ions between the half-cells.

How it works:

• Oxidation at the Anode: Zinc metal releases electrons and dissolves as Zn²⁺ into the solution. 

• Reduction at the Cathode: Copper ions from the solution accept electrons and deposit as metallic copper on the electrode.   

• Electron Flow: The released electrons flow through the external circuit from the zinc anode to the copper cathode, creating a usable current.

• Ion Movement in the Electrolyte: The salt bridge ensures that sulfate ions (SO₄²⁻) move from the copper half-cell to the zinc half-cell to balance the charge.

Comparison with the Potato Battery:

In the potato battery, copper and zinc take on the role of the electrodes, while the acidic cell sap acts as the electrolyte. The chemical processes are similar: zinc is oxidized, releases electrons, and the copper electrode receives them. Again, electrons flow through the external circuit, creating a small voltage, just like in the Daniell cell. However, in the potato battery, the copper electrode is not in a Cu²⁺ solution, so the electrons are transferred to the acid. This results in the reduction of protons (H⁺) and the formation of hydrogen gas.

Once the zinc is depleted or the electrochemical reaction reaches equilibrium, the battery can no longer provide current.