Driving on starch?
Using sugar contained in corn or potatoes to build hydrogen-powered fuel cells has already been done. But now, a team of U.S. researchers has developed a new sugar-to-hydrogen technology. Why not put the starch inside the tank of your car? With the help of 13 specific enzymes, "a car with an approximately 12-gallon tank could hold 27 kilograms (kg) of starch, which is the equivalent of 4 kg of hydrogen. The range would be more than 300 miles, estimates one of the researchers. One kg of starch will produce the same energy output as 1.12 kg (0.38 gallons) of gasoline." The beauty behind this idea is that no special infrastructure would be needed. Starch could be distributed by your local grocery store.
Above is a picture of Percival Zhang, an assistant professor of biological systems engineering at Virginia Tech, posing in front of the raw material he plans to use, and who was a leading researcher for this project, along with other members of his group (Credit for picture: Zhang Group).
Here are some details about this research project.
Polysaccharides like starch and cellulose are used by plants for energy storage and building blocks and are very stable until exposed to enzymes. Just add enzymes to a mixture of starch and water and "the enzymes use the energy in the starch to break up water into only carbon dioxide and hydrogen," Zhang said.
A membrane bleeds off the carbon dioxide and the hydrogen is used by the fuel cell to create electricity. Water, a product of that fuel cell process, will be recycled for the starch-water reactor. Laboratory tests confirm that it all takes place at low temperature -- about 86 degrees F -- and atmospheric pressure.
And what about the advantages of this method?
Over the years, many substances have been proposed as "hydrogen carriers,"such as methanol, ethanol, hydrocarbons, or ammonia – all of which require special storage and distribution. Also, the thermochemical reforming systems require high temperatures and are complicated and bulky. Starch, on the other hand, can be distributed by grocery stores, Zhang points out.
"So it is environmentally friendly, energy efficient, requires no special infrastructure, and is extremely safe. We have killed three birds with one stone,"he said. "We have hydrogen production with a mild reaction and low cost. We have hydrogen storage and transport in the form of starch or syrups. And no special infrastructure is needed."
But will this be an energy efficient process? Of course yes, say the researchers.
"What is more important, the energy conversion efficiency from the sugar-hydrogen-fuel cell system is extremely high – greater than three times higher than a sugar-ethanol-internal combustion engine,"Zhang said. "It means that if about 30 percent of transportation fuel can be replaced by ethanol from biomass as the DOE proposed, the same amount of biomass will be sufficient to provide 100 percent of vehicle transportation fuel through this technology."
This new step towards a future hydrogen economy has been abundantly commented this week. Here is an arbitrary selection of three articles on this subject.
- In "Gassed up: A new, green way to make hydrogen," The Economist comments that "Dr Zhang's method is a step towards that goal. Though starch is a refined and relatively expensive starting point, [Dr Zhang's] method is more efficient than any of the alternatives that begin with plant matter. It is also a proof of principle. Now, he and his team are working on a still longer chain that starts with cellulose. This is a much more abundant glucose polymer than starch, but is also much harder to break down." (May 24, 2007)
- In "Starch diet could power car of the future," New Scientist adds that this technology could be used for other purposes. "If the financial support is sufficient, within three to five years, this technology will be applied to high-end markets such as cellular phone and laptop batteries," says Zhang. "After another three to five years it will be integrated with hydrogen-fuel-cell vehicles. If everything goes well, we will see the first real-size sugar car on the way after eight to ten years." (Catherine Brahic, May 24, 2007)
- And in "Running Cars on Hydrogen Made from Starch," Technology Review reports that "Zhang notes that employing starch to make hydrogen would be a much better use of the available corn than turning it into ethanol: fuel cells can be three times more efficient than ethanol-burning internal combustion engines. Nevertheless, he sees starch as a temporary solution. Zhang is also developing a version of the process that starts with cellulose, found primarily in the nonfood parts of plants." (Kevin Bullis, May 24, 2007)
Finally, if you prefer scientific facts to comments, this research work has been published on May 23, 2007 by PLoS ONE under the name "High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway." Here is a link to the full article.
Sources: Susan Trulove, Virginia Tech News, May 22, 2007; and various websites
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