Micro fuel cell packs power

Researchers from the California Institute of Technology, the University of Southern California and Northwestern University have built a propane-driven fuel cell that's not much bigger than a watch battery, but lasts much longer.

Two of the fuel cells would have enough power to drive an MP3 player. The devices could also be used to power tiny flying robots, and to provide power for electronic devices like laptop computers and cameras, according to the researchers.

Propane packs twice as much energy for its weight as methane, which is more often used for fuel cells.

The challenge of making a small-scale propane fuel cell work was figuring out how to get the device to generate enough heat to sustain the chemical reaction that extracts energy from fuel.

The researchers met the challenge using a catalyst that generates enough heat to maintain the reaction at 500 to 600 degrees Celsius, and a heat exchanger to keep the heat within the device. The catalyst is a porous film of ruthenium metal particles and cerium dioxide. The catalyst speeds the chemical reaction that extracts energy from propane mixed with oxygen.

The researchers' prototype consists of a pair of propane fuel cells positioned back-to-back in a nested pair of quartz tubes that channel the fuel to and away from the cells. The prototype generates 1.44 volts.

The researchers' prototype requires that it be heated to 300 degrees Celsius in an oven to jump-start the reaction. The researchers are working on making the reaction work from a more practical starting temperature.

The technology could be made practical in 5 to 15 years, according to the researchers. The work appeared in the June 9, 2005 issue of Nature (A Thermally Self-Sustained Micro Solid-Oxide Fuel-Cell Stack with High-powered Density).