Introduction: Lime Jello, Yeast and Carbon Paper Fuel Cell
Can Jello Brand Instant Gelatin replace coal fired power plants? Probably not but it can be used to build a demonstration microbial fuel cell from common materials. This is a fun classroom or rainy day project, tie multiple cells together and use the power to light an LED. You'll probably need a joule thief as well. Output voltage and current are a function of cell volume and carbon electrode size.
Here's how it works, we're going to mix a little Jello brand Instant Gelatin with some Fleischmann's Active Yeast and a few drops of plant food. Once that solidifies we're going to cut out some fun Jello squares (yes, they still jiggle) and, using the carbon paper as electrodes, we're going to tap the energy produced by the yeast to create electricity.
This is an innovative form of the popular single cell microbial fuel cell or MFC. The gelatin serves a variety of useful purposes, including MFC container, fuel source and electrolyte. The yeast will feed primarily off of the sugar in the gelatin mix while the gelatin seals out ambient oxygen.
As you can see we started off with about 500 mV which ain't bad for some Jello and yeast...
Now let's get started!
Step 1: Bill of Materials
Not much to this one.
The hardest item to find, believe it or not, was actual old fashioned carbon paper. I ended up ordering over the net since I couldn't find it in my local stores. Make sure you get real carbon paper since that is used for the carbon electrode and will significantly impact the performance of your MFC.
You'll need some instant gelatin. You want the kind with sugar in it (or that you add sugar to). I used Jello brand Instant Gelatin in lime flavor for reasons which will become obvious. Any gelatin should do, including unflavored gelatin with a cup or so of sugar dissolved in it.
You'll need some yeast. I used Fleischmann's Active Dry yeast for no particular reason other than it was there.
A candy thermometer or some other good way, including judgement, to keep from putting the yeast until the water has cooled down to 100 degrees or so.
A container, I used a square glass one that was handy. It should be convenient for cutting squares out of.
If you have some handy a little Instant-Gro or Shultz's plant food adds useful supplements to the medium.
Now that we have everything let's make some Jello...
Step 2: Preparing the Microbial Media
Nutrient media is a fancy name for gelatin, sugar, yeast and some nutrients.
Grab a bowl and pour the Jello mix into it.
Measure out two cups of water and place them off to the side with some ice cubes to cool it down.
Bring two cups of water to a strong boil. Make sure you get the full two cup measure of boiling water. Add this to the gelatin mix and stir for about two minutes. Make sure that all the contents are fully dissolved.
When the candy thermometer shows that the temperature has cooled to around 100 degrees add one packet of yeast and stir to dissolve. Stir for several minutes allowing the media to cool naturally. After about 5 minutes pour into the pan or mold you are using. Use the cold water to rinse out any yeast bits stuck to the side and pour into the mold. Mix well and place in refrigerator or freezer to set.
Step 3: Prepare the Electrodes
Once the jello has fully set ( a couple of hours ) we're ready to assemble our fuel cell.
First have we to make the carbon electrodes we will use to tap power from the MFC.
Cut a 2.5 inch strip from the bottom of the carbon paper, then cut 2.5 squares from that strip. This will form our electrodes.
Place one of pieces of carbon paper on a paper plate or other holder for your MFC. If you have an Easy Carbon Electrode you can place that on the anode, otherwise you can connect a lead from your MM directly to the anode.
Step 4: Charging and Operating
Okay now that we've got our two carbon paper electrodes cut out and the anode positioned We take our Jello out of the fridge and cut a square approximately 3 inches on a side.
Place that more or less carefully on top of the anode assembly. Now place the other piece of carbon paper on top of the Jello square. This is the cathode.
Attach one lead from your MM to the anode lead, attach the other to the cathode. As you can see in the intro picture I got an initial reading of approximately 500 mV which has subsequently dropped to about 280 mV on an open circuit.
You will notice that this ubiquitous green Jello just looks the part, don't it?
Plus, you know, it's really a green project...