Wednesday, September 13, 2006

Better Fuel Cells for Laptops

Adding a chemical found in antifreeze to fuel cells could provide a longer-lasting alternative to batteries in portable electronics.

By Kate Greene

Batteries are the bane of consumer electronics users. They provide only a limited amount of power, take hours to recharge, and over time become less long-lasting. For years, engineers have been eyeing fuel cells--devices that produce electricity by mixing a fuel with oxygen molecules--as a longer-lasting alternative power supply. But the technology has always encountered hurdles that keep it from being as practical and cost effective as batteries.

Now researchers at Arizona State University's Biodesign Institute in Tempe have developed a technique that could help make better fuel cells for laptops, military-grade communication devices, and, potentially, cell phones. In research presented yesterday at the American Chemical Society meeting in San Francisco, Dominic Gervasio, associate professor in the Center for Applied Nanobioscience at Arizona State, and his team showed that by adding a chemical found in antifreeze to sodium borohydride--a liquid used to store hydrogen, the molecule that powers fuel cells--they can make a longer-lasting fuel cell. The resulting fuel could power a laptop twice as long as any battery on the market, while allowing room temperature operation, unlike many other fuel cells.

Fuel cells for portable devices have been gaining traction in the past few years as the technology behind them has steadily improved. Indeed, they've now reached beyond research labs, and made their way into various forms of production. Millennium Cell, an Eatontown, NJ-based company, supplies fuel cells for military applications. And by year-end, New York-based Medis Technologies plans to offer a consumer fuel cell device designed to instantly recharge standard batteries in cell phones, MP3 players, and laptops.

Sodium borohydride, the solution used by Millennium Cell, Medis, and the Arizona State team is becoming a popular choice to store hydrogen for portable fuel cells, says Gervasio. One reason is that it's used with the most-established fuel cell design. This type of fuel cell works by combining hydrogen with oxygen from the air to produce electric current. In addition, systems that use sodium borohydride can be made as small as conventional batteries because the solution stores a large amount of hydrogen in a small volume. Moreover, it's a relatively safe liquid that isn't flammable. "You could take a match and put it out in it," Gervasio says.

But to succeed as a replacement for batteries, these fuel cells have to prove themselves significantly better than the batteries they aim to replace, says Gervasio. Currently, most sodium borohydride fuel cells produce only slightly more electrical energy per volume of fuel than conventional batteries, he says. To increase the performance of their fuel cell system, Gervasio and his team knew they needed to increase the amount of hydrogen available to the fuel cell from the sodium borohydride solution.

Micro-fuel-cell systems generally contain three parts: a cartridge of fuel, a hydrolysis chamber where hydrogen is extracted from the liquid fuel, and a fuel cell where hydrogen mixes with oxygen, creating electricity. In the Arizona State researchers' system, a mixture of water and sodium borohydride is pumped from the cartridge into the hydrolysis chamber, which contains a catalyst. The catalyst sets off a chemical reaction that liberates hydrogen from the sodium borohydride solution, and also creates byproducts that are pumped out of the chamber and back into the fuel cartridge to be disposed later.