Quick screening yields better catalysts.

Fuel cells that convert methanol and water into electricity may one day offer a clean, portable source of power for electric vehicles. To date, however, the materials used as catalysts to perform this conversion haven't been efficient enough to make such fuel cells practical.

Now, researchers have developed a technique to screen potential catalysts rapidly. They mix together small amounts of metals in different proportions and then identify visually which combinations work best. With this method, "we can spot catalytic compositions that we would never have considered" with an approach based on chemical theory, says Eugene S. Smotkin of the Illinois Institute of Technology (IIT) in Chicago.

Smotkin had been looking for new materials by trying to deduce which metals would blend well with platinum to catalyze efficiently the breakdown of methanol in a fuel cell. "I had some success," says Smotkin, "but the process was laborious and time-consuming." Thomas E. Mallouk of Pennsylvania State University in State College suggested that they look instead at a large number of catalysts simultaneously.

Using an ink-jet printer, Mallouk and his colleagues laid down hundreds of daubs of different metal combinations on conductive carbon paper. They immersed the array of spots in a mixture of methanol, water, and a fluorescent dye that glows under acidic conditions. When they applied an electric voltage, the best metal combinations triggered an electrochemical reaction that increased the acidity of the solution around those spots. Simply by observing which spots glowed, the researchers could identify good candidate materials.

Smotkin then tested the most promising ones in fuel cells and found that a particular blend of platinum, ruthenium, osmium, and iridium is much more active than the platinum-ruthenium alloy now considered the best catalyst available. Using the old strategy, "I never would have considered iridium," he says. Smotkin, Mallouk, and their colleagues report their findings in the June 12 Science.

Robert C. Haushalter of Symyx Technologies in Santa Clara, Calif., says scientists there have been examining the same kinds of materials with similar methods (SN: 11/1/97, p. 278).

After using this technique to search for methanol fuel cell catalysts, the researchers at IIT and Penn State began developing such combinatorial methods to find catalysts for cells that run on hydrogen and oxygen, which power some of today's electric vehicles (SN: 11/13/93, p. 314). Methanol fuel cells are "at least a decade away," Smotkin says.