PHILADELPHIA Chemical engineers at the University of Pennsylvania have developed a prototype fuel cell that the first to run on a readily available liquid fuel source, in this case ordinary diesel fuel. The work nudges fuel cells closer to viability, offering the promise of compact, portable power sources that offer much more bang for the buck than combustion engines or existing batteries.

Scientists, corporations and the military are all interested in fuel cells, which are far more efficient and less polluting than other energy sources. Work to develop commercial fuel cells, however, has been hindered by the limited fuel sources on which they have been known to run.

"There used to be a saying that you could run a fuel cell on any fuel as long as it hydrogen," said Raymond J. Gorte, professor of chemical engineering at Penn and the lead author of a Journal of the Electrochemical Society paper reporting the finding.

Gorte and colleague John M. Vohs, professor and chair of chemical en-gineering at Penn, shook the fuel cell world in March 2000 with the publica-tion of a Nature paper in which they reported developing a fuel cell that could run on butane, the first fuel cell to operate on a fuel other than hydrogen. With the development of a fuel cell that runs directly on liquid diesel of the type sold at gas stations, the team has sidestepped the thorny problem of "reforming" fuels to hydrogen to run fuel cells.

"In our earlier work, we were unable to feed liquid diesel to the fuel cell because we did not have a means for vaporizing fuels that have a low vapor pressure at room temperature," Gorte said. "This paper demonstrated that we could feed these liquids to a fuel cell using a method analogous to a fuel injector in an internal combustion engine and still get stable operation of the fuel cell."

Much past research with fuel cells has focused on the messy question of how best to process, or "reform," available hydrocarbon fuels such as diesel into pure hydrogen, an expensive and inefficient proposition. The Penn fuel cell is the first to run directly on hydrocarbons, without requiring complicated reforming into hydrogen either within the device itself or at specialized filling stations. Generating electric power through controlled electrochemical reactions rather than combustion, its only emissions are water, carbon dioxide and heat.

Smaller than a penny, the prototype fuel cell developed by Gorte, Vohs, graduate student Hyuk Kim and postdoctoral researcher Seungdoo Park operates in a furnace set at 700 degrees Celsius. A commercial, self-contained fuel cell would ideally generate that heat itself using the fuel placed in it.

Although unlikely to replace household batteries for small appliances and portable electronics, researchers have suggested that fuel cells might be appropriate for powering cars and laptop computers.

"We are excited by the progress that Professor Gorte and his colleagues are making in the area of direct oxidation of hydrocarbon fuels using solid oxide fuel cells," said David Bauer, team leader for the Solid Oxide Fuel Cell project at the Ford Research Laboratory in Dearborn, Mich. "The ability to utilize conventional fuels with little or no reforming is particularly important in transportation applications where fuel storage and system packaging are such critical issues."

Fuel cells could also make possible electric generators that operate on propane or butane. Gorte team is interested in developing a relatively small, five-kilowatt fuel cell. Such a unit, placed in a home basement, could be used to generate electricity from natural gas, using the excess energy to heat the home or its hot water.

"It much more efficient to produce energy on-site than it is to make it many miles away," Gorte said.

The U.S. military regards fuel cells as a possible source of portable "palm power" for soldiers carrying electronic devices. Together with Honeywell, Penn researchers have recently been awarded $1.8 million by the U.S. Army and the Defense Advanced Research Projects Administration to develop a coffee-can-sized fuel cell capable of generating power equivalent to 50 D-cell batteries. The military is particularly interested in diesel-run fuel cells because diesel low vapor pressure makes it less explosive and therefore safer; the Penn fuel cell also runs on the hydrocarbons toluene and n-decane.

DARPA has indicated to the team that it would like fuel cell technology to find civilian applications. "We believe this is very doable and that this technology should be very easily modifiable for many applications," Gorte said.

Gorte, Vohs, Kim and Park work with solid-oxide fuel cells was funded by the Office of Naval Research and published in the July issue of JECS.