Using a stew of enzymes culled from several organisms, researchers have developed a way to convert starch, available from numerous sources including corn and potatoes, into hydrogen gas at low temperatures and pressures. The method produces three times more hydrogen than an older enzymatic method does, suggesting that it might be practical to use such enzymes to produce hydrogen for fuel-cell vehicles.
While fuel-cell vehicles are appealing because they emit no pollutants, it’s been a challenge to find clean and affordable ways to produce, transport, and store hydrogen to fuel them. Most commonly, hydrogen is extracted from fossil fuels. Making hydrogen by electrolyzing water is energy intensive and can be expensive. The new system improves on other experimental methods for creating hydrogen from biomass by using low temperatures, making it potentially more convenient and energy efficient.
The researchers–from Virginia Tech, in Blacksburg, VA; Oak Ridge National Laboratory; and the University of Georgia, in Athens–combined 13 commercially available enzymes isolated from yeast, bacteria, spinach, and rabbit muscle. The work is available online in PLoS ONE, a journal published by the Public Library of Science. The hydrogen comes from two sources: the starch and the water used to oxidize the starch. The enzymes facilitate chemical reactions in which the water and starch can be completely converted into hydrogen and carbon dioxide, says Y. Percival Zhang, professor of biological systems at Virginia Tech. (The carbon dioxide released is offset by the carbon dioxide captured by plants that provide the starch.)
The new system produces a higher yield of hydrogen than previous experimental systems that used enzymes for converting sugars into hydrogen. But while the yield of hydrogen is high, so far the rates at which the gas is produced are extremely low. That’s in part because the researchers used off-the-shelf enzymes and have not optimized the system, Zhang says. The scientists’ next project will include analyzing each stage of the process in detail to find the rate-limiting steps.
For example, one of the enzymes may be producing a by-product that slows down later steps, says Michael Adams, professor of biochemistry and molecular biology at the University of Georgia. The researchers would then look for other enzymes, or modify current ones, to minimize the by-product. They will also look for enzymes that can operate at higher temperatures. “If you increase the temperature by 10 degrees, most times you can increase the reaction rate twofold,” Zhang says.
One of the first applications of the system, Zhang says, could be generating hydrogen for fuel cells in portable electronics. The starch could be a safer way of storing energy than using methanol, a current leading option for such small fuel-cell systems. He estimates that it will take about six to eight years to improve the rates enough for such applications. Eventually, he hopes to use his process to solve one of the biggest current problems with hydrogen fuel-cell vehicles: fitting enough hydrogen on board to compete with gasoline-powered vehicles.