In a microbial fuel cell, bacteria break down organic matter, releasing electrons and protons into a solution. The protons migrate through a membrane, while the electrons enter a cathode and pass through a circuit that delivers them to the protons on the other side. There, protons--ionized hydrogen--and electrons react with oxygen to produce water, at the same time generating a voltage that keeps the electrons flowing, so the device produces a small amount of electric power (SN: 2/4/06, p. 72).
In the absence of oxygen, and with the help of a metal catalyst, the protons and electrons will instead combine into hydrogen gas. However, such hydrogen-producing bioreactors require an external voltage to pull the electrons from one side to the other, and so far have been very inefficient:
A 1-liter bioreactor would normally produce 4 milliliters of hydrogen per day, says Bruce Logan of Pennsylvania State University in University Park.
By switching to a different membrane and using phosphates to ferry protons through it, Logan and his colleague Shaoan Cheng have now created a prototype bioreactor that can produce hydrogen 300 times as fast as before, with bacteria that can feed on a variety of foods, including glucose and cellulose. It produces almost three times as much energy--in the form of hydrogen gas--as it uses electrically, the researchers write in the Nov. 20 Proceedings of the National Academy of Sciences.
"This is an important step;' says Derek Lovley of the University of Massachusetts in Amherst, who's working on genetically engineered microbes that can produce hydrogen more efficiently.--D.C.
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|Date:||Dec 1, 2007|
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