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How Bacterial Hydrogen Fuel Cells Work


pennstate_microbialfuelcells_500.jpg“When bacteria are placed in the anode chamber of a specially-designed fuel cell that is free of oxygen, they attach to an electrode. Because they do not have oxygen, they must transfer the electrons that they obtain from consumption (oxidation) of their food somewhere else than to oxygen — they transfer them to the electrode. In a MFC these electrons therefore go to the anode, while the counter electrode (the cathode) is exposed to oxygen. At the cathode the electrons, oxygen and protons combine to form only water. The two electrodes are at different potentials (about 0.5 V), creating a bio-battery (if the system is not refilled) or a fuel cell (if we constantly put in new food or “fuel” for the bacteria).

“By adding a small amount of voltage (0.25 V) to that produced at the anode in a MFC, and by not using oxygen at the cathode, you can produce pure hydrogen gas at the cathode! This is a modified MFC process we call the “bioelectrochemically assisted microbial reactor” or BEAMR process. This is a MFC operated in a completely anaerobic manner that uses the potential produced by bacteria, plus a small additional voltage (which could be produced by a MFC or other ways), that produces hydrogen through the recombination of protons and electrons at the cathode. Theoretically we need only 0.41 V to achieve this, so if the potential produced by bacteria could be increased (currently it is 0.3V), and the overpotential (losses) at the cathode reduced, we could one day produce hydrogen gas without additional voltage.”

The process produces 288% more energy than the electricity required to extract it. Compared to water hydrolysis, for example, which is only 50% to 70% efficient making it require more input energy than the extracted hydrogen yields, this process is far more desirable. It can be shown that even using enough of the harnessed energy to sustain the reaction, 144% more energy is produced. This makes the microbial soup solution a real application for energy generation.

The researchers indicate another possible use for these kinds of microbial cells is for manufacturing fertilizer. Instead of using current methods, which involve trucking in fertilizer made in factories, very large farms could begin using microbial cells. They would take wood chips processed through a common practice used today, along with nitrogen from the air, to produce ammonia or nitric acid. These can both be used as sources of fertilizer, or as feed material to make ammonium nitrate, sulfate or phosphate.

source: here

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