Let's just get this out of the way first. EWWWWW (not ewe)! OK, done. I'm not entirely sure what "rumen fluid" is, but I already don't like the sound of it. Apparently, it is fluid from the largest chamber of a cow stomach. Reseachers at Ohio State are using the "microbe-rich" fluid, which is "from a living cow, [extracted] through a cannula, a surgically implanted porthole that leads directly into its rumen" (I told you it sounds gross). They then filled one compartment of a fuel cell with "this microbe-rich fluid and with cellulose." There is another compartment in the fuel cell separated by a material that allows an electrical charge to move from one chamber to the other. All right, continuing on: "the anode chamber [is filled] with cellulose and with microbes derived from rumen fluid. Electrons are released as the microorganisms break down the cellulose." The second chamber is the cathode, which is filled "with potassium ferricyanide, a chemical that acts as an oxidizing agent and helps close the electrical circuit by accepting electrons from the cathode electrode. Once the circuit is closed, electrons flow from the anode to the cathode, creating electricity."
These fuel cells will run as long as the bacteria is fed with cellulose, meaning biomass like grasses or woodchips. The researchers in Ohio have had this latest prototype actively producing electricity for three months. In other words, these fuel cells are completely sustainable. The researchers are also working out how to create the rumen fluid in a lab, as opposed to "collecting" it from cows. Maybe 'cause that's just gross. This sounds like cow vomit to me, and that's just not cool.
[Source: The Ohio State University]