The inspiration for this project came from an article on Wired.co.uk about 4 teenage Nigerian girls who created a means of separating elemental Hydrogen from human urine: the concept was that this Hydrogen would be used to produce electricity in a generator. However, both the urine and the Hydrogen needed to undergo numerous purification processes before it could be used to power said generator. Oliver Warr - a researcher at Manchester - remarked upon the problems of electrolysis of urine which "is not simply composed of urea". The electrolytic process produces quite a lot of Chlorine which will often bond with the Hydrogen forming Hydrochloric acid. This got me thinking...was there a better way of harnessing the chemical potential energy in urine? Was there a method that required much less purification if any? Yes, there is. Henceforth, I introduce you to the Air/Salt/Urine battery: this is a primary cell that can run off air or salt or urine (which has a high salt content).The air/salt/urine requires no purification and the cell works by utilising a difference of electronegativity of electrodes to shift electrons and create current...I hope you enjoy the upcoming Instructable. I did my best to make this using readily-available, common materials so that it could theoretically be produced on perhaps a larger scale in developing countries...
Step 1: Gather the Materials
The first step is to gather the materials...
For this project, you will need as follows:
- Plastic bottle
- Carbon-Zinc Batteries (I used 16 Panasonic ones)
- Aluminium Foil
- Table Salt (lots of it!)
And the tools you will need are:
- 2.8mm drill bit
- 6mm drill bit
- A freezer
- Soldering iron
- Hot Glue Gun (and glue sticks)
Step 2: Extract the Carbon Rods
- Tear apart the outer metal casing of the battery.
- Carefully and slowly pull out the carbon rod in the center. This is very brittle and will snap and become nearly useless if you do not do this bit with care.
- Run an old cloth along the rod to clean off all the messy Manganese Dioxide (MnO₂) electrolyte.
- Lightly sand the surface of the rod to increase surface area and ensure all the MnO₂ has been removed.
- Repeat this process for the all the batteries and their Carbon rods.
Step 3: Prepare the Bottle
- Make sure the bottle is empty. If not, drink whatever tasty beverage is in it. Remove all the labels and then rinse it thoroughly.
- Fill the bottle up to just a few centimeters from the top with cold water. Squeeze it until the water level is at the top and screw the lid on, you want as few air bubbles as you can possibly get. We do this to leave room for the bottle to expand when we freeze it without splitting and spilling.
- Leave the bottle in the freezer for 24 hours. As water freezes, it expands which increases the pressure; we can take advantage of this as it gives us a nice taut surface to drill through.
- Depending on how many carbon rods you now have, drill through the bottle all the way around the same number of times as you have carbon rods. Most rods have a diameter of about 3mm, so I used a 2.8mm drill bit in order to achieve a tight fit and avoid leakage!
- Once your holes are drilled. Place the bottle outside and wait for about 24 hours so that all the ice will melt away. The reason I wouldn't just put the bottle into really hot water is that this could cause the bottle to contract/expand, ruining the project. Now take the bottle top, and drill about a 6mm hole straight through the top of it. This will make space for our cathode (-).
Step 4: Create the Anode(s)
- Insert all the carbon rods into the holes in the bottle. You want them roughly half way towards the center.
- Using a hot-glue gun, glue them in place.
- Wire the carbon rods together in a snake pattern, i.e. each rod should have only one wire going to and from it.
Step 5: Create the Cathode
- Roll up a tube of aluminium foil a few centimeters longer than the bottle. This is our negative terminal (cathode).
- Insert it into the bottle and through the cap. This is our cathode(-).
Step 6: The Electrolyte
This type of cell theoretically works with an AIR electrolyte and so that is what I used for my first test.
I then made a supersaturated Sodium chloride (table salt) solution and tested with that.
Step 7: The Results!
Congratulations! You have completed the project.
My initial test with air generated: 1.1V @ 0.1mA
My test with supersaturated saltwater generated: 0.98V @ 9mA
Yes, this voltage and current level is atrocious. Regardless, I created this project as a proof of concept that this type of cell could be created with everyday items...I most certainly not claim to be an expert in this field and I am sure there are numerous ways the project could have been done differently leading to higher voltage/current.
Thank you very much for reading! If you try this, please share that with me! I would love to see your creations/variations and your ideas on how this project could be improved as I intend to revise it in the future!