Advanced (Long Life) Air Battery

Make a battery that works with air and saltwater

NOTICE: This science project experiment is a simplified version of the air battery project available at ScienceProject.com. Pictures and excerpts of information are published here with permission.

Introduction: 

Batteries have been made with many different chemical compounds. Scientists often try to make batteries that provide more energy and last longer. Many of such high quality batteries are commercially available today. They are used in flashlights and electronic devices such as radios, watches, computers and calculators.

Making a battery is always an exciting science project. Your home made batteries can be used as chemistry, physics or electricity project. 

Click here to see the instructions for the Standard Kit.

How the battery is made?

A battery is made of two different electrodes inserted in a chemical compound. A chemical reaction between the electrodes and the chemical compound produces electricity. For example if you insert a copper rod and an iron rod in a cup of orange juice, that will be a battery. In this example copper rod and iron rod are the electrodes and the orange juice is the chemical compound or electrolyte. The problem is that the electricity produced by such a battery is too little and has no practical use and you cannot use it to light up a light bulb. The saltwater battery described in this project guide can light up a light bulb for a few seconds. When the light goes off, you can simply empty the used salt water and add fresh salt water to get light again. By adding a small amount of hydrogen peroxide you can get more light and the light will last longer.

List of materials you need:

This is the list of materials you need and come in the advanced air battery kit.
  1. Four Iron Electrodes IRON2
  2. Four Magnesium Electrodes MGFLAT
  3. Super Bright LED light 8CR2V20MA
  4. Two pairs of insulated copper wire with alligator clips on the ends 9119
  5. Analog multimeter with no battery YG188
Additional optional materials you may use:
  1. Three or four large cups or 400ml beakers
  2. Strong saltwater (Containing about 20% salt)
  3. Hydrogen Peroxide

If you don't have the materials for this project you may order them now.

What is a good title for my project?

You can call it "Air battery", "Salt water battery", "electricity from air" or "electricity from the salt water".

Procedure:

  1. Set the multimeter to 2.5 DCV so it can read DC Voltage. (DC stands for direct current)
  2. Fill up a cup with saltwater to about one inch to the top.
  3. Insert one magnesium electrode and one iron electrode in the cup and make sure they are not touching each other.
  4. Connect one end of the black alligator clip wire to the magnesium electrode and connect the other end of the wire to the black probe of the multimeter.
  5. Connect one end of the red alligator clip wire to the Iron electrode and connect the other end to the red probe of the multimeter.
  6. Read and record the voltage (of your first saltwater battery).
    In this battery the magnesium electrode is the negative pole. (that is why we connected that to the black wire that is usually used for negative). The Iron electrode is the positive pole. (That is why we connect it to the red wire which is usually used to represent positive).
  7. Disconnect the multimeter and connect the LED light. Connect the shorter leg to the black wire (negative) and the longer leg to the red wire (positive). Does it light up? Record your observation.
     
  8. Repeat the steps 2 and 3 with a second cup to make your second saltwater battery. Place that next to the first battery.
  9. Use any color wire with alligator clips to connect the magnesium of one battery to the iron of the other battery. This is called connection in series.
  10. Connect the remaining iron and magnesium electrodes to the multimeter, read and record the voltage. (remember to use red for positive or iron, and black for negative or magnesium).
  11. Disconnect the multimeter and connect the LED light. Connect the shorter leg to the black wire (negative) and the longer leg to the red wire (positive). Does it light up? Record your observation.
     
  12. Repeat the steps 2 and 3 with a third cup to make your third saltwater battery. Place that next to the first two batteries.
  13. Use any color wire with alligator clips to connect this battery to your series. remember that the magnesium of one battery connects to the iron of the other. Now you will have a series with three batteries.
  14. Connect the remaining iron and magnesium electrodes to the multimeter, read and record the voltage. (remember to use red for positive or iron, and black for negative or magnesium).
  15. Disconnect the multimeter and connect the LED light. Connect the shorter leg to the black wire (negative) and the longer leg to the red wire (positive). Does it light up? Record your observation.
     
  16. Prepare and connect the fourth battery and repeat the same measurements and observations with the series of four batteries.
  17. the magnesium of one battery to the iron of the other battery. This is called connection in series.
Three saltwater batteries were enough to light up this LED light. The light stayed on for more than 24 hours. The long life of this battery is due to the use of flat electrodes (that will last longer) and use of LED light that requires less electric current.

Picture on the right shows three air/saltwater batteries linked in series and lighting up an LED light for more than 24 hours.

How can I get more light?

  1. Make sure your electrodes are not touching each other.
  2. Make sure there is nothing blocking the space between the electrodes.
  3. Make sure that the alligator clips are not touching the salt water.
  4. Both electrodes must have the maximum possible surface contact with salt water.
The oxygen in the air may not be enough for your demonstration and you may get a dim light. 

In this case you may add some oxygen (in the form of hydrogen peroxide) to the salt water. That should immediately increase the light.

A cup is relatively small. If you have access to a larger container, you will get a better result. In a larger container, it is easier to secure the electrodes in two opposite sides so they will not touch each other.

Where to buy the material?

The main components of this project are available as a set in MiniScience.com online store and KidsLoveKits.com. This set will only include the essential components. You must have plastic containers or cups, saltwater and hydrogen peroxide to complete your materials.

Part# AIRBATX

The electricity produced in this way may be used to light up an LED light for more than 24 hours.

Identifying the polarity or direction of electricity is especially important when you are trying to light up an LED. 

Each LED has 2 legs. One is longer than the other. The longer leg must be connected to the positive pole of the battery or Iron. The shorter leg must be connected to the negative  electrode or Magnesium. 


If you don't have the materials for this experiment, you can order it now.

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Does it really work?

Although a saltwater battery is not as strong as a real battery, it can produce visible light on a low voltage light bulb. It is also safer than batteries that use many harmful chemicals.

What chemicals do I need?

The only chemical that you need is Sodium Chloride (NaCl) also known as table salt. This is the chemical that you usually have it at home. If not, you can buy it from grocery stores. Good quality, pure and inexpensive packages of salt are often marked as kosher salt. You also need water (H2O).

How does it work? What is the chemical reaction?

When Iron and magnesium are placed in water, multiple chemical reactions happen that contribute to the movements of electrons from magnesium electrode towards iron electrode. During these processes Iron electrode oxidizes to Iron oxide and magnesium electrode reduces to magnesium hydroxide.

Here's what is happening in more details:

  • Magnesium have a tendency to react with water and form magnesium hydroxide. To do this each magnesium atom must lose one electron (and become Mg+ ions). While the magnesium electrode is loosing electrons it will form the negative pole.
  • The electrons from the magnesium atoms combine with the hydrogen ions in the water and form H2 molecules (Hydrogen gas). We see the hydrogen gas as bubbles forming on the magnesium.
  • On the other electrode, the iron that is oxidized by air and is now in the form of Fe++ ion needs to receive two electrons to change back to iron. This will create shortage of electrons in the iron side and make the iron a positive pole.