Micropower heats up: propane fuel cell packs a lot of punch.

Portable electronics such as laptops and MP3 players could soon run on miniature fuel cells that consume propane, the same fuel used in gas barbecues. In search of longer-lasting alternatives to conventional batteries, a team of researchers has developed just such a device.

"A propane-driven fuel cell could be the same size as a lithium battery but last 10 times longer," says Paul Ronney of the University of Southern California in Los Angeles.

Other groups have previously developed fuel cells for portable electronics. However, most of these run on methanol (SN: 9/7/02, p. 155). Propane and other large hydrocarbons are more desirable because their larger molecules pack more energy and can be easily stored as liquids rather than as pressurized gases. A small cartridge of liquid propane under moderate pressure could feed a fuel cell for days. Most batteries require recharging after only several hours of continuous use.

In the June 9 Nature, Ronney, Sossina Haile of the California Institute of Technology in Pasadena, and Scott Barnett of Northwestern University in Evanston, Ill., describe their dime-size fuel cells. A primary focus of their work was to design a fuel cell that could heat itself up to the 500[degrees] to 600[degrees]C required to convert propane into electricity. So far, such fuel cells work only when continuously heated by an external source.

To build a self-heating feature into their design, the researchers coated one of the fuel cell's electrodes with a catalyst--a mixture of ruthenium and cerium dioxide--that enhances the breakdown of propane by oxygen. That reaction releases heat and also produces hydrogen and carbon monoxide, which then undergo electrochemical reactions in the fuel cell. The result is electricity, with carbon dioxide and water as waste products.

In one experiment, the catalytic oxidation of propane in the fuel cell produced enough heat to sustain the fuel cell for 200 hours. In another test, a pair of the fuel cells, wrapped in thermal insulation, produced sufficient power to operate a 1.5-volt MP3 player.

"This is fabulous work," says Jesse Wainright of Case Western Reserve University in Cleveland. To compete with lithium-ion batteries. however, the fuel cell's efficiency would have to be increased tenfold, he estimates.

Another glitch with the prototype is that to initiate the catalytic reaction, the fuel cell first has to be heated to 300[degrees]C for about a minute inside a furnace. Once the cell reaches that temperature, it generates its own heat.

Ronney says that he and his colleagues are searching for a fuel additive that could ignite the reaction at room temperature. The ultimate goal is to create a self-starting fuel mixture, a small percentage of which would be the ignition fuel and the rest of which would be propane.