A cow dung fuel cell
Researchers at Ohio State have concocted a fuel cell that produced between 300 and 400 millivolts, thanks to microbial action in cow dung. Granted, that's less than the energy produced by a AA battery, but you don't have to go to a convenience store for the basic materials either.
The electricity is produced when microorganisms break down cellulose, making the Ohio State project the first cellulose-based fuel cell, according to the university.
The fuel cell derived from an ongoing study of biofuels at the university. A recent study published by the university found that that the microbes in about a half a liter of rumen fluid--fermented, liquified feed extracted from the largest chamber of a cow's stomach--can produce about 600 millivolts of electricity. The fuel cell was a practical application of the findings.
Extracting electricity from biological waste products has been around for a while. Some California dairy farms derive much of their power from the stuff lying on the ground. Some biofuel advocates believe that decayed matter could be used to produce methane or other products which could then be used in cars or to heat homes. Others, however, note that the energy that goes into producing biofuels can outweigh the gain.