May 20th  2002

THE POWER OF SMALL TECH

Source:David Pescovitz

But that’s about half the efficiency needed for a methanol fuel cell to power portable devices such as cell phones or laptop computers, or military equipment such as stand-alone or wearable sensors. And the fuel processor is developed enough for Battelle, which operates the national lab for the U.S. Department of Energy, to begin discussions with companies to commercialize the technology.

“The target is 15 to 20 percent,” said Evan Jones, a staff development engineer at PNNL and a lead researcher on the project. “We want to get it as high as we can.”

The team fired up its fuel processor-fuel cell system in January,  and within  a week of testing began to seeing what Jones calls ”quite good” efficiencies. They shared some of their findings at the International Conference on Micro-reaction Technology held in New Orleans in March.

Batteries used in today’s handheld devices are at least three times more efficient than fuel cells, but have two drawbacks: They offer  less punch per pound, technically  known as energy density; and they lose their charge and can be recharged only a finite number of times before they must be replaced.

Fuel cells have a much higher energy density and only require a refill of hydrogen or a hydrocarbon source to produce electricity. Their high energy density more than makes up for their low efficiency, said Robert Savinell, director of Case’s Yeager Center for Electrochemical Sciences and a collaborator in the fuel cell project.

For instance, a lithium battery produces about 100 watt-hours per kilogram (Wh/kg) and with improvements could double that figure, he said. Pure methanol gets 6,000 Wh/kg. Methanol mixed with water, the combination used in the PNNL-Case platform, chalks up 3,000 Wh/kg.

“If you get only 20 percent efficiency, that’s 600 watt-hours per kilogram,” Savinell said.

Size and temperature pose the biggest challenges for the engineers, said Jones and Savinell. Unless the fuel cell uses pure hydrogen, it needs a high-temperature catalytic fuel processor or reformer to strip hydrogen atoms from their chemical companions in fuels such as methanol, diesel or butane. But the smaller the reformer gets, the more overall surface is exposed, and that leads to problematic heat losses, Jones said. “It’s like trying to keep a little match lit,” he said.

PNNL and Case Western’s solution was to use methanol combined with water, which is converted in the reformer to hydrogen and carbon dioxide gases in temperatures as low as 200 to 400 degrees Celsius. Diesel, by contrast, takes about 900 degrees Celsius while butane needs 500 to 900 degrees. The hydrogen is channeled from the reformer into the fuel cell, where an electrochemical reaction produces electricity and water.

The fuel processor itself is compatible with other miniaturized fuel cells, making it a candidate for commercialization. Bob Silva, who oversees commercialization efforts at PNNL, said the lab hopes to name commercial partners by Sept. 30. “We want to see this in the market as soon as possible,” he said.