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Microbial Hydrogen Generation
Jamais Cascio, 25 Apr 05

Although some fear that the hydrogen economy, should it come, will be built atop of nuclear power plants, and others hope that solar and wind will provide enough juice to crack hydrogen from water, it may well turn out that the ideal source of hydrogen for fuel cells is the lowly bacteria.

We've mentioned microbial fuel cells before, tiny powerhouses that generate electricity while cleaning wastewater. But researchers at Penn State have taken the microbial fuel cell off in a new direction, pulling hydrogen out of wastewater at a rate four times greater than the standard fermentation process, and ten times greater than straight electolysis.

In their paper, the researchers explain that hydrogen production by bacterial fermentation is currently limited by the "fermentation barrier" -- the fact that bacteria, without a power boost, can only convert carbohydrates to a limited amount of hydrogen and a mixture of "dead end" fermentation end products such as acetic and butyric acids.

However, giving the bacteria a small assist with a tiny amount of electricity -- about 0.25 volts or a small fraction of the voltage needed to run a typical 6 volt cell phone -- they can leap over the fermentation barrier and convert a "dead end" fermentation product, acetic acid, into carbon dioxide and hydrogen.

Logan notes, "Basically, we use the same microbial fuel cell we developed to clean wastewater and produce electricity. However, to produce hydrogen, we keep oxygen out of the MFC and add a small amount of power into the system."

[...] The researchers call their hydrogen-producing MFC a BioElectrochemically-Assisted Microbial Reactor or BEAMR. The BEAMR not only produces hydrogen but simultaneously cleans the wastewater used as its feedstock. It uses about one-tenth of the voltage needed for electrolysis, the process that uses electricity to break water down into hydrogen and oxygen.

The process does produce CO2, but as it's derived from biomass, the setup is closer to carbon neutral than other carbon dioxide generating methods of distilling hydrogen.

The big potential here is suggested in the final line of the excerpt: this process is significantly more efficient than straight electrolysis as a means of separating out hydrogen from water. One of the strongest arguments made in support of the use of nuclear plants for hydrogen generation is that the electricity generated by solar and wind will be insufficient to generate enough hydrogen. If this process does in fact work as described, it could be the breakthrough making solar & wind a competitive path to hydrogen generation.

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Oh wow. This is pretty amazing. and if we threw a little GM in there, made these things twice as powerful...

hell, there's a viable solution. our power plants of the future could look like waste water plants with a few small solar panels out front.

Posted by: Andrew on 25 Apr 05

First, voltage is not equivalent to power. Although these devices use a low voltage, you can be quite sure that it will use much more power than a cellphone. It will use less power than electrolysis, exactly how much is not well-represented in the Environ. Sci Technol. article, since there are no controls for cells growing without a power supply or sterile electrodes connected via power supply.

Second, microbial catalysis of just about anything is very slow. If you want to build one of these things beneath your solar panel or windmill, and continually take up the power generated, it will have to be very large.

Finally, although the catalysis of the anode is capable of responding to demand and is extremely cheap (since the microbes are doing the catalysis), the hydrogen is produced by the platinized cathode, and the hydrogen protons to make hydrogen gas are conducted by a Nafion membrane. Both Nafion and platinum are very expensive, and both degrade fairly quickly when you throw wastewater at them.

Although he mentions that you can have very low loadings of platinum and still be effective, fuel cells going backwards or forwards still need a lot of work before they will be anything close to competing with burning acetate (or ethanol or biomass or any other hydrocarbons you are throwing away) very quickly at very high temperatures over a metal catalyst.

Posted by: Ben Hunt on 26 Apr 05



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