Diesel-Fueled Fuel Cell Making Big Advances

Diesel Fuel News, Sept 17, 2001 by Jack Peckham

Chemical engineering researchers at University of Pennsylvania last week reported a significant breakthrough in diesel-fueled fuel-cell power that eventually could pave the way for practical and efficient auxiliary, portable and stationary power systems.

For the first time ever, the researchers discovered that it's quite feasible to use diesel fuel without reforming it to hydrogen prior to introduction in a fuel cell, and without the costly precious metals required of proton-exchange membrane (PEM) fuel cells as typically proposed for vehicle power.

"There used to be a saying that you could run a fuel cell on any fuel as long as it's hydrogen," quipped U-Penn. chemical engineering professor Ray Gorte, who first published the findings in a peer-reviewed science periodical, Journal of The Electrochemical Society, earlier this year.

Since then, various researchers have talked of direct-methanol fuel cells as a possible future replacement for relatively costly hydrogen. But now it looks like conventional liquid fuels -- with none of the deadly toxicity of methanol nor the huge refueling infrastructure cost obstacles of hydrogen or natural gas -- might surpass competitors in the race for practical, low-cost fuel cell applications.

At the U-Penn. labs, researchers built a solid-oxide fuel cell (SOFC) for testing hydrocarbons including typical gasoline components (n-decane and toluene) and a synthetic diesel fuel provided by gas-to-liquids developer Syntroleum.

This SOFC required development of a scheme for vaporizing denser fuels such as diesel, employing a device "analogous to a fuel injector," Gorte said.

While it's conceivable that future development could lead to transient-type applications, the initial focus is orr steady-state stationary or portable power, Gorte told us.

The synthetic diesel used in the tests was a zero-sulfur variant of conventional diesel, but further testing now shows that more conventional diesels, containing some sulfur, wouldn't be a show-stopper for this SOFC, Gorte said in an interview.

Not only will ordinary diesel work, but so will ordinary unleaded gasoline, he said. "We have another paper coming out, and this shows it's pretty tolerant of sulfur," Gorte said, which makes this SOFC device a potentially blockbuster invention.

SOFCs generate electricity via reduction of [O.sub.2] to [O.sup.2-] anions at the cathode, transfer of the anions through an electrolyte, then oxidation of fuel by [O.sup.2-] anions at the anode. Typical SOFC anodes contain nickel in a yttria-stabilized zirconia ceramic-metal (cermet) composite, but this formulation would cause a big problem with diesel fuel.

* Avoiding Carbon Formation

"The primary limitation for direct oxidation of hydrocarbons in an SOFC is the propensity of Ni to catalyze carbon formation," the researchers reported in their paper. But they discovered that by substituting copper for nickel, they could avoid carbon formation and enhance catalytic properties.

Still, a lot of work needs to be done to achieve more realistic hydrocarbon conversion rates, as well as temperature and fuel-concentration control to avoid tar formation found under the test conditions. Otherwise, tars formed by the process would block the anode pores and decrease performance.

Besides commercial applications such as trucking (auxiliary power for heating, cooling and freight compartment temperature control) or distributed power, the breakthrough means potentially huge advantages for the military.

That's why the U.S. government (through Defense Advanced Research Projects Agency, DARPA) is funding a $1.8 million, three-year R&D project employing the U.-Penn. fuel cell, together with technology development experts at Honeywell.

The military initially sees applications for so-called "palm power," allowing soldiers to carry around small, 20-watt, 12-volt (DC) electronic devices for many days, without worrying about losing power as is typical with batteries. The single battlefield fuel for the U.S. military is a light diesel fuel, so that's why the U.-Penn. fuel cell is key to the project. Scale-up to larger, higher-power-level devices should be fairly simple once the initial 20-watt system is proven, as DARPA researcher Robert Nowak explains.

While such systems initially might be more costly than batteries (though batteries are less durable or efficient), advanced fuel-cell technologies, once widely employed, could make a huge difference on the battlefield. That's because new studies show it can cost the military up to $400/gallon to deliver fuels to battle fronts, because of complex, dangerous and often difficult logistics in delivering fuel for military aircraft, vehicles and power systems, Nowak said.

In some instances, the Air Force actually burns up 84% of the fuel load carried before it can make a final delivery, and up to 90% of the mass of battlefield materiel delivered is actually fuel.

Electric power reliability and power quality increasingly becomes critical for the high-tech, electronics-dependent military, further boosting prospects for reliable, fuel-cell powered distributed generation, Nowak told us.