Make a Microbial Fuel Cell (MFC) - Part III

Intro: Make a Microbial Fuel Cell (MFC) - Part III

This 5 gallon single chamber microbial fuel cell uses inexpensive conductive cloth to provide a silver catalyst and a styrofoam permeable membrane.

Operation of a single chamber MFC is complicated by oxygen poisoning resulting from the conflicting requirements of the anaerobic population and the cathode requirement for dissolved O2. This design attempts to limit oxygen poisoning by using a brush type carbon electrode combined conventional carbon paper to provide a gas barrier without limiting free flow of the microbial medium.

The use of styrofoam as the permeable membrane is novel as far as I can tell.

Conductive cloth is used to provide an inexpensive silver catalyst to promote oxidation at the cathode. We use silver plated conductive cloth from lesseremf but any silver plated material should do. The use of silver as a catalyst is based on the research done for the air cathode in an aluminum air battery and is experimental in an MFC.


As you can see from the picture I got about 90 mV across the open circuit after charging and assembling the cell. The extraction of power from an MFC scales directly in proportion to two things, population density and surface area of the electrode surface at the cathode and anode.
Power will continue to rise as the population density increases.

STEP 1: Bill of Materials

This is a simple bill of materials and assembly. Because we are building a single chamber MFC we won't need to create a salt bridge or anything like that.

1 5 gallon plastic pail with lid - I got my mine at Home Depot on sale for $2.97 plus the lid
8 in styrofoam disc - Cut out of packing material or I'm using one I got at Michael's
Use loose styrofoam if you can get it. You want air to pass easily through
Anaerobic Microbial Culture - I'm using "Microbe Lift" brand Septic Tank and Cesspool Treatment
Yeast should also work
1 Package of large aquarium charcoal filter pads. I'm using Fluval brand 4 PLUS filters
Silver coated conductive cloth - http://www.lessemf.com/fabric.html I'm using the "Stretchy silver coated sheer nylon weave". This is used as a catalyst to facilitate oxyidation at the air cathode. It also as the electron collection grid.
A couple of wire leads with clips or some way to attach them to the carbon pads.
Two sheets of carbon paper. This is used to get good mechanical connectivity between the pads.

STEP 2: Create the Styrofoam Cathode

The styrofoam cathode which sits at the top of the MFC chamber is a gateway that admits air and vents biogas resulting from the microbe action.

As you can see in the picture it is a sandwich. The bottom layer is styrofoam, next is a layer of conductive cloth, then two carbon pads laid side by side. This is followed by another layer of conductive cloth, then the carbon paper. As you can see in the picture the carbon paper is placed with the shiny side facing the conductive cloth.

The electrode assembly is attached to the styrofoam by means of 4 toothpicks and a strip of clear plastic tape.

STEP 3: Prepare the Microbial Chamber

Now take the lid and carefully cut out the inner circle. This will be an almost perfect fit for the styrofoam disk.

Next prepare the anode assembly on the bottom of the pail ( see picture ). This is done by laying down an 8x5 inch piece of carbon paper, followed by a 8x5 inch piece of conductive cloth then the two remaining pads from aquarium filter.

This assembly is buoyant and tends to float when the solution is added. I found it necessary to attach this assembly to the bottom of the pail with clear plastic tape. I think super glue and/or a slightly different assembly might be easier.

Okay now we're ready to charge this puppy up and see what happens...

STEP 4: Assembling and Operating the MFC

Okay Tesla let's turns microbes into electrons....

Put in the rest of your shredded paper so that the anode is liberally covered.

I went down to Big Lots and picked up a couple of 3L bottles of inexpensive soda to use as microbial media but almost anything can be used. Make yourself a nice 5% sugar water solution or use a mild vinegar solution.

I chose these because I wanted the 3L bottles for the next generation of my Wind Turbine and thought it would make a good sugar based medium. I certainly wasn't going to drink the stuff. Also the acid in the soda will help to break down the paper.

After you've added the soda place the bucket out in the afternoon sun for a couple of hours to vent the gas. The fill the pail the rest of the way with water. The styrofoam will float on the water and press against the lid to obtain a seal (more or less).

Attach the second lead to the carbon electrode on the styrofoam. Float the styrofoam ( carbon side down ) in the water and the two leads around it through the hole in the lid.

Add 1/4 cup or so of Microbe Lift to charge the MFC and then press the lid down firmly.

Simply attach a 220 ohm resistor across the leads and begin measuring voltage.

Comments

[egbertfitzwilly]

I'd be interested in getting those links if you have them handy.... Mine is special because its posted on instructables....Other than that, and experimental use of styrofoam as the permeable membrane, its just your run of the mill 5 gallon single chamber microbial fuel cell....

[jdgable09]

Out of Curiosity, do you think graphite foil could replace the silver fabric for the anode and cathode? I am doing a project where I am trying to make it more efficient and the silver is a bit too expensive for our scaled-up version.

[zaschita1]

Could you tell me how to increase current for at least domestic use? After all, the current strength is very low. It is a question of scaling MFC.

[SHOE0007]

A better way is to make copper electrodes plated with cobalt from cobalt (II) chloride for the negative and the positive would be platinum electrodes. The electrolysis of cobalt chloride would create a plating of cobalt metal over the copper strippling. Since fumes of cobalt (MAY) be released this must be done outside with a gas mask. Plenty of ventilation is required too and this is because some chlorine is produced. The cobalt will react with air to form cobalt oxide which would eventually form cobalt plated (cobalt hydroxide).

[SHOE0007]

For agar containing 17.5% hydrogen peroxide gels this worked for 6 hours.

6 pm = 10 mA.

7 pm = 9 mA.

8 pm = 8 mA.

9 pm = 7 mA.

10 pm = 6 mA.

11 pm = 5 mA.

The problem is the fairly quick release of hydrogen peroxide and the copper and stainless steel electrodes. Perhaps using platnium metal electrodes instead of copper and stainless steel may work since they will not react with anything.

[SHOE0007]

I am thinking of adding 1 mole Potassium ferrocyanide trihydrate in knox gelatin. Bacteria will slowly break down the potassium ferrocyanide trihydrate and react with gels of H202. Gels will contain knox gel and 20 ml water. Once the temperature reaches 60 degrees C add 20 ml of 35% H202. I will see if this work or not?!!

[SHOE0007]

the voltages were near 810 mV or so. The total power when 3.5% hydrogen peroxide was added was 21 mW.

[Micheal hook]

First time I come to hear about 5 gallon single chamber microbial fuel cell. It is good for users knowledge. It is scientifically as well as logically approved and appreciable. It is just for experimental. Fuel mileage is very important and essential for an engine, we can say it is the life of that engine. Maximize your fuel efficiency-

http://vimeo.com/114647629

[Burgess_Shale]

Isn't the silver toxic to the bacteria? Did this continue working for a while?

[Dr Qui]

Please don't take this question the wrong way, I'm not trying to disprove the concept just curious.

Is it possible to power any electronics as is or would you need bigger or more of them?

Is there a large scale application?

[egbertfitzwilly]

First let me say I'm not really a scientist I just play one on Instructables...You might also like my Jello and Yeast project. Yes, this technology can produce production levels of power. My next generation cell will be a significant improvement over this and well suited to septic tank or municipal waste storage tanks. My personal target application is the 66% of the world who have no electricity at all. Scalability seems to be double vectored,multiple cells in series or larger quantities of media. The leading researcher in the field is Logan at Penn State and Hui up at Oregon State has done some fascinating work. Both have published in the Journal of Power Sources Additional information as well as links to other researchers in the field can be found at microbialfuelcell.org.

[goatboy825]

Awesome:

What about the graphite fabric and chicken wire one they are using in Africa?

It seems to me that the other side of this power generation is a DIY storage battery or bank of DIY capacitors...

Everyone is focused on lightweight protability for cars. Like you I am thinking of homes that don't move and all the recycled stuff (like buckets, styrofoam, beer cans and milk jugs)

How about a jumbo low-tech battery or capacitor to store the fuel cell power in?

[Dr Qui]

I'm kinda baffled by it.

Does the yeast culture feeding on the paper and sugar from the soda make an electrolyte type substance that powers the cell?

Would it be more efficient at the equator than saw Canada or Ireland?

You are indeed a scientist, you work is pure science, much cooler than anything they ever showed us at school.

The best science and technology comes from men in sheds who often make groundbreaking discoveries.

[egbertfitzwilly]

Thank you for these kind words. What forms the electrolyte has been discussed in some detail. I'm of the opinion that the sugar in Jello serves a dual role as electrolyte and feed with the jello acting as an agar like bridge. I don't know that the carbon paper decomposes fast enough to provide nitrogen to the yeast, its possible that supplemental nitrogen of some form might increase the yield. The barbon paper will, of course, eventually decompose leaving no trace of its existance. Output will also be affected by the environment. The happier the yeast are the higher the output. I noticed that power dropped overnight and resumed in the morning, this correlates nicely with the ambient temperature.

[egbertfitzwilly]

Voltage dropped significantly overnight the first night. It varies quite a bit during the day but is steadily rising. I have no idea how long it will take a container of this size to reach peak output. At the moment I'm seeing a steady 60 mV and rising.

[CoolKoon]

How about the current? And since many months have passed since this assembly, how much energy have you managed to extract from it (Wh or something)?

[egbertfitzwilly]

This device was disassembled long ago. All of these devices are experimental in nature and rarely survive more than a few weeks. Overall my results from this design were disappointing and did not compare well with the two chamber model.

I believe the 5 gallon pail ( and larger tanks ) are best suited for a single cell approach where chamber "seperation" into aerobic and anaerobic portions is controlled primarily by depth.

[CoolKoon]

Yeah, I'm even kinda surprised you've managed to separate the two processes, as that's kinda hard to do with off-the-shelf materials. This reminds me of the process of making sour cabbage (a local delicacy I guess), where you shred the cabbage, but it into a barrel/vat, add some salty water, cover the whole thing with a plastic bag and press it down for better seal (my grandma used a big rock for this). I know that the fermentantion process that takes place there is anaerobic (the bacteria involved use nitrogen in their metabolism instead of oxygen IIRC), and it's relatively slow (it takes a few weeks for the cabbage to turn sour). What I still don't get though is the need for dissolved O2. I thought that the only thing you need in an electrolyte are ions (molecules that will act as charge carriers) or am I missing something?
How did this two chamber model of yours perform then?

[egbertfitzwilly]

As I understand it, and it is by no means clear that I do, the salt bridge provides transport for hydrogen ions which carry a negative charge. These combine with dissolved O2 to produce water and release an electron or two. The dissolved oxygen can be provided by a number of sources including chemicals, algae byproducts or "gas uptake in a liquid" which is the long way to say the surface absorbs oxygen from the air.

I suspect that if a salt bridge were connected to the cabbage bucket a charge could be generated and multiple cells could be wired in series. Grandma would be proud....

[CoolKoon]

Hmmmm.......this goes contrary to much of the stuff I've learned about the chemical reaction involved in my chemistry class (hmmm........quite a few years ago). I mean water is a dipole molecule, which is caused by the big electronegativity of the oxygen atom (it almost strips the H atoms of their lonely electrons and keeps them for itself, making the O part negative). Therefore when you dissolve something in water, it's actually "disassembled" by the water molecules into positively and negatively charged ions. Take for example table salt: the water molecules separe it to H+ and Cl-. This separation remains while the water molecules are present.
A salt bridge is usually used to facilitate ion exchange between two separate electrolytes. You see the charge carriers are not the water constituents but the ions dissolved in it, otherwise some distilled water could work as an electrolyte too (without prior charging, of course). I'd say that the charge carriers (ions) give up their electrons by merging with the materials of the electrodes itself. Now I'm sure things are a bit different when microbes are involved, but I don't know much about the mechanics involved. So the question remains: if the microbes can survive only in an oxygen-free environment, what's the O2 there for?
As for the sour cabbage electricity thing I thought about that too. Unfortunately my grandma passed away about a year ago as the result of a final stroke. She never recovered fully even from their second one though (wasn't the same person anymore), but have I tried that before (attaching electrodes to sour cabbage and testing it with my multimeter) she would've surely been convinced that I've gone crazy and banned me from the basement (by hiding the key) :P No sour cabbage has been for a long time (probably for practical reasons as well, because it wouldn't be eaten I guess) so I don't think I could try it out (especially because none of my parents like my experiments either :S). Still, it's a really interesting idea that's worth a try.....