Tiny fuel cell

Engineers have created a propane-burning fuel cell that’s almost as small as a watch battery, yet many times higher in power density.

Led by Sossina Haile of the California Institute of Technology, the team of engineers says that two of the cells have sufficient power to drive an MP3 player. If commercialized, such a fuel cell would have the advantage of driving the MP3 player for far longer than the best lithium batteries available.

According to Haile, who is an associate professor of materials science and of chemical engineering at Caltech, there are three advances that make the technology possible.

Two of the advances were made at Caltech. The first was to make the fuel cells operate with high power outputs at lower temperatures than conventional hydrocarbon-burning fuel cells. The second was to use a single-chamber fuel cell that has only one inlet for premixed oxygen and fuel and a single outlet for exhaust, which makes for a very simple and compact fuel cell system.

The third involves catalysts developed at NorthwesternUniversity that cause sufficient heat release to sustain the temperature of the fuel cell.In addition, a linear counter-flow heat exchanger makes sure that the hot gases exiting from the fuel cell transfer their heat to the incoming cold inlet gases.

Although the technology is still experimental, Haile says that future collaborations with design experts should tremendously improve the fuel efficiency. In particular, she and her colleagues are working with David Goodwin, a professor of mechanical engineering and applied physics at Caltech, on design improvements. One such improvement will be to incorporate compact “Swiss roll” heat exchangers, produced by collaborator Paul Ronney at USC.

As for applications, Haile says that the sky is literally the limit. Potential applications could include the tiny flying robots in which the defence funding agency DARPA has shown so much interest in recent years. For everyday uses, the fuel cells could also provide longer-lasting sources of power for laptop computers, television cameras, and pretty much any other device in which batteries are too heavy or too short-lived.