Though the method has not yetbeen evaluated for economic feasibility on a large scale, chemist MahdiAbu-Omar said it could offer solutions to several problems facingdevelopers of fuel cells, which are looked upon as a potentialreplacement to fossil-fuel burning engines in automobiles. Thetechnique requires only water, a catalyst based on the metal rhenium(REE-nee-um) and an organic liquid called an organosilane, which can bestored and transported easily.
"We have discovered a catalystthat can produce ready quantities of hydrogen without the need forextreme cold temperatures or high pressures, which are often requiredin other production and storage methods," said Abu-Omar, an associateprofessor of chemistry in Purdue's College of Science. "It is possiblethat this technique could lead to fuel cells that are safe, efficientand not dependent on fossil fuels as their energy source."
Abu-Omar'sresearch team, which includes Purdue's Elon A. Ison and Rex A. Corbin,published their findings today (Wednesday, Aug. 31) in the Journal ofthe American Chemical Society.
Hydrogen is the most plentifulelement on Earth and, once isolated, is a clean-burning fuel thatproduces neither greenhouse gases nor toxic emissions. Because hydrogencan be used for electricity production, transportation and other energyneeds, many see a changeover to a "hydrogen economy" from our oil-basedone as the solution to global energy problems. But before hydrogen canbe used as fuel, it must be extracted from other substances that areoften fossil fuels, and then stored safely in sufficient quantities. Ifthese problems can be solved, hydrogen-powered generators, known asfuel cells, might replace internal combustion engines everywhere fromelectrical plants to cars.
Abu-Omar and his colleagues were notconcentrating on these problems when they began studying organosilanes,a group of organic molecules that have been slightly modified in thelaboratory. But as commonly happens in science, he said, a projectoften takes researchers in different directions than originallyanticipated.
"Initially, we were concerned with finding usefulcatalysts to convert these silicon-based fluids into silanols, anothertype of substance that is valuable in the chemical industry," he said."It's the sort of work chemists do all the time, and it's usually ofinterest only to other chemists. But sometimes the byproducts ofconversions are as interesting as what you wanted in the first place."
Abu-Omar'steam took a compound based on rhenium, a comparatively rare metal oftenobtained while mining copper, and added it to the organosilane in thepresence of water. Over the course of an hour, the organosilane changedcompletely into silanol, leaving the water and rhenium catalystunchanged. But the team also noticed there was a gas bubbling from themixture.
"It turned out to be pure hydrogen," Abu-Omar said. "Thereaction is not only efficient at creating silanol, but it alsogenerates hydrogen at a high rate in proportion to the amount of water."
Theteam estimates that about 7 gallons each of water and organosilanecould combine to produce 6 1/2 pounds of hydrogen, which could power acar for approximately 240 miles.
"The big question is, of course,whether it would be economically viable to create organosilane fuels inthe quantities necessary to power a world full of cars," Abu-Omar said."As of right now, there simply isn't enough demand to make more thansmall volumes of this liquid, and while it's a relatively easy process,it's not dirt cheap either."
But, Abu-Omar speculated, producingorganosilanes in larger quantities would bring the price down, and thebyproduct – silanol – also could be recycled or sold to lessen theoverall cost.
"On today's chemical market, silanol is even moreexpensive than organosilanes are, but their value would of coursedecline as well if there were suddenly millions of gallons of them onthe market," he said. "These are the sorts of questions that economistswould have to look at, and we have other questions of our own, such aswhether these reactions can be carried out on naturally occurringhydrogen sources."
Abu-Omar said this question might prove to be the more relevant one as investigations continue.
"Ithink the big point here is that hydrogen can be produced from waterand a form of organic matter," he said. "If this rhenium-based catalystcan do the trick on organosilanes, perhaps we can find other catalyststhat can generate hydrogen from garbage, or from biomass left over fromthe harvest."
The current findings, he said, demand that the method be scrutinized more carefully.
"Fornow, we've demonstrated the initial premise that we can produce andstore hydrogen on demand with this method," he said. "It's a greatstart, but we need to know more about the economic and ecological priceof doing this on a larger scale."
Abu-Omar is affiliated withPurdue's new Energy Center in Discovery Park. The center will focus ondeveloping economically and environmentally sound energy sources, andon helping to change policies and perceptions about the way we useenergy. More than 75 campus experts in disciplines from engineering,science, agriculture and liberal arts will contribute to the effort.
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