Microbial fuel cell (bio battery)

Summary

Lots of science and lots of fun!

This is work in progress, part of my home science project. Since there is a lot of literature considering this topic I will here describe just technical details of this design. Useful links to the literature are included below.  So far I managed to run LED flashlight and small toy car on this battery. Multiple batteries can be connected in series or parallel to obtain one’s needed voltage or current. Making this design working does not require any special skills. This type of battery is a great teaching tool in various fields of science such as biology, chemistry, electronics and programming. To get most of these batteries I use small device/circuit called joule thief (link how to make one included) and also I monitor their voltage continuously using Adafruit data logger (link how to make one included).

This type of producing electricity is interesting in remote locations where electricity is not available.

Read all about microbial fuel cells (MFCs) in: [1,2]

Design:

  Here are two versions of same design one of which is all-in-one version and the other is version with separable upper part. Choose version depending on your 3D printer and preferences. If using printer that can't print more than 3 cm in the air choose version with separable upper part cause every kind of support here is not of any help.

 

While printing this were my extruder settings:

Infill: 10%

Layer thickness:  0.27mm

Without any support

And speed of printing was on maximum as seen on photos (I recommend lower speed of printing and/or post processing in terms of sanding or glossing over using acetone)

 

Explanation:

 

On the battery’s upper side are four tubes that are intended to be used for filing the battery with needed fluids. There are also three slots, two on each side used for inserting electrodes and one in the middle used for inserting semi-permeable membrane. To the design are added three thin frames that are, when printed, folded in half and serve as support for electrodes and membrane (see pictures).

 

 

Additional materials needed:

 

Pair of electrodes (I use carbon cloth because of huge surface area but other materials such as steel or aluminium should also do the job)

Pair of wires for connecting loads to the battery

Semi-permeable membrane (I use commercially available membranes (link included) but cellophane or so called salt bridge (which is basically salt in jelly) should work fine)

Microorganisms: to fill into anode (-) chamber; you can use baking yeast mixed with sugar and water (available in every grocery store), mud or other to you available source (consult the literature)

Some oxidizing agent to fill cathode (+) chamber (I use potassium ferricyanide in 0.02 M concentration (link to the shop included. If using this chemical compound consider safety precautions allthough it is reolatively small concentration)

Optional: rubber tubing for filling fluids into the battery

 

NOTE:

If you are not familiar with using chemicals and semi-permeable membrane you can modify this design by placing one electrode in slot for membrane (middle slot) leaving one side of microbial fuel cell empty. To maximize the cell’s like this performance fresh air should be pumped into the empty part to allow the chemical reactions to happen (using aquarium pump or something similar).

 

Literature/links

[1]

http://web.mit.edu/pweigele/www/SoBEI/Info_files/Logan%202006%20Environ%20Sci%20Technol.pdf

 

[2]

http://www.engr.psu.edu/ce/enve/logan/bioenergy/research_mfc.htm

Joule thief

http://cdn.makezine.com/make/wp_joule_thief.pdf

Adafruit data logger:

https://cdn-learn.adafruit.com/downloads/pdf/adafruit-data-logger-shield.pdf

Semi-permeable membranes:

http://www.membranesinternational.com/tech-cmi.htm

Potassium ferricyanide

http://www.sciencecompany.com/Potassium-Ferricyanide-100g-P6372.aspx

 

For additional information search the Internet typing “microbial fuel cell” or “MFC”