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Device to speed chemists' studies of catalysts
Monday, June 15, 1998 By Byron Spice, Science Editor, Post-Gazette
Someday, the streets may be filled with electrically powered, environmentally friendly cars powered by fuel cells, but fuel cell technology isn't quite ready. If and when that day comes, scholars tracing the breakthroughs that led to commercially viable fuel cells may cite the day Tom Mallouk took a hacksaw to his inkjet printer.
It was an act not of anger or frustration but of ingenuity. By modifying his $250 Apple Stylewriter, Mallouk, a chemist at Penn State University, built an apparatus that could rapidly test hundreds of combinations of metals that might be used as catalysts - materials that speed up chemical reactions.
As he and his colleagues reported last week in the journal Science, this makeshift device identified one combination that, based on preliminary analysis, might be 40 percent to 100 percent more efficient than the best known catalyst used in one type of fuel cell.
"I don't want to overstate the case and say we've solved the problem," said Eugene Smotkin, a chemical and environmental engineer at the Illinois Institute of Technology, who collaborated with Mallouk. The catalyst appears to be the best available for converting methanol into electrical energy, but it's still not good enough to make methanol-air fuel cells commercially viable.
But Mallouk's discovery promises to reduce dramatically the time chemists must spend evaluating thousands of possible catalysts.
It's an approach known as combinatorial chemistry. Rather than make and test compounds one by one, combinatorial chemistry takes the shotgun approach, testing hundreds of compounds simultaneously. It's an approach that is already revolutionizing the search for new pharmaceuticals.
By marrying this approach to electrochemistry, Mallouk and two students, Erik Reddington and Anthony Sapienza, were able to evaluate 640 potential catalysts simultaneously.
"It's a technique with tremendous power," said Michael Ward, an electrochemist at the University of Minnesota. A single graduate student, evaluating catalysts by conventional methods, might take four years to complete the same task, he guessed.
Speed has become important as auto manufacturers and states face increasing pressure to reduce vehicle emissions. Car makers face mandates to sell electric cars in California and Massachusetts, yet General Motors reports sluggish demand for the $34,000, battery-powered EV1 car it began selling and leasing last year in California.
Manufacturers are thus investing hundreds of millions of dollars in fuel cell development. Unlike batteries, which require frequent and lengthy recharging, fuel cells can be replenished quickly by simply adding more fuel, much like filling a conventional car with gas. Unlike internal combustion engines, fuel cells emit only water and carbon dioxide, not the nitrogen oxides and volatile organic compounds that lead to smog.
The National Aeronautics and Space Administration has used hydrogen-oxygen fuel cells since the Gemini program of the 1960s. This fuel cell technology is well developed, Smotkin acknowledged, but the use of high-pressure hydrogen and oxygen gas will probably not be practical for most motor vehicles.
Last year, the U.S. Department of Energy and A.D. Little Co. announced the development of a fuel cell that uses gasoline as a source of hydrogen. Unlike hydrogen gas, gasoline is readily available and easily handled.
The work by Smotkin and Mallouk is directed at what could be a second generation of fuel cell that would use methanol. Though methanol, like gasoline, can be produced from petroleum, it can also be made from renewable sources and thus would have some environmental advantages.
Several problems must first be solved, however. One of them is to improve the efficiency of the catalyst -- the material that helps break methanol down into carbon dioxide, electrons and hydrogen nuclei, or protons. A second reaction within the fuel cell combines the electrons and protons with oxygen from the air to form water.
After three decades of research, the best known catalyst for breaking down methanol is a platinum-ruthenium alloy. But researchers would like to find an alloy that is more resistant to carbon monoxide, a compound that is produced as part of the process of producing carbon dioxide. Carbon monoxide, Smotkin said, poisons the catalytic reaction, bringing the chemical reactions to a halt.
But when contemplating different metals, or adding a third, fourth or fifth metal to the mix, the number of potential combinations becomes daunting.
Mallouk had read about other experiments using inkjet-like systems to spray samples of metals together for testing. But he realized that it might take a year and $1 million to build such a device. Having neither, he had a graduate student pick up the Apple inkjet printer and hack open the four inkwells. Instead of magenta, cyan, yellow and black inks, they used the jets to spray drops of platinum, ruthenium, osmium, iridium and rhodium salts onto a carbon backing.
Each test sample was about the size of a lower-case "o."
Mallouk then made a second innovation. Rather than individually measure the electrical current of each of these hundreds of dots, he connected all of the dots onto a single circuit, painted them with a dye that fluoresces in response to acid and immersed the array in a bath of methanol.
An active catalyst, Mallouk said, produces acid. So he and his students needed only to look at the array and note which dots were lit up and which ones were brightest to determine the best catalysts.
Smotkin and his research team in Illinois are now evaluating the best candidate, a combination of platinum, ruthenium, osmium and iridium. He doubts that it will be good enough for commercial use, but the approach he and Mallouk developed should rapidly ferret out better candidates.
"It's like throwing a fishnet out into an ocean of fish," Smotkin said. "You don't necessarily get the biggest one on your first try."
The same techniques could be used for other types of catalysts, both those used in other types of fuel cells and those used in an array of commercial processes. It might be used to find better materials for rechargeable lithium batteries, for instance, or more efficient catalysts for producing chlorine or nylon feedstocks.
"Problems like that are just waiting to be solved with those methods," Mallouk said.
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