Filling in the gaps. Ultrafine palladium wires (connected to silver contacts at each end) swell in the presence of hydrogen, allowing a current to flow.

Conserving Energy With Nanotechnology

Using nanotechnology, researchers have developed the world's fastest and most energy-efficient hydrogen detector. The detector consists of an array of hundreds of ultrathin metal wires that become less resistant when exposed to whiffs of hydrogen. It could become a key component of motors fueled by hydrogen.

Abundant and clean to burn, hydrogen makes sense as an alternative fuel. But existing hydrogen sensors are too sluggish to monitor a continuous stream of hydrogen gas, so combustion engines can't precisely vary the amount of hydrogen they need at a given time. Consequently, when hydrogen is used as fuel, it's not burned efficiently. A sensor that quickly and accurately tells the engine how much hydrogen it needs could solve that problem.

To build a speedy hydrogen detector, chemist Reginald Penner at the University of California, Irvine, teamed up with researchers at Montpellier University in France. As they report in the September 21 issue of Science, the scientists made the detector with palladium, a metal extremely sensitive to hydrogen. Penner then designed an array measuring 10 microns across and made up of nanoscale wires, to maximize the surface area exposed to the gas and thereby speed the sensor's response time.

The scientists tested their new detector by exposing it to traces of hydrogen. The wires rapidly absorbed the gas and swelled slightly, which closed miniscule gaps and allowed an electrical current to flow more easily. When researchers removed the hydrogen from the chamber, the detector sensed the change instantly, reopening the gaps and releasing hydrogen from the wires in milliseconds--thousands of times faster than any current technology. When attached to an engine, the sensor could vastly improve energy efficiency.

"It's a very beautiful piece of work," said Paul Bohn, a chemist at the University of Illinois, Urbana-Champaign. Bohn hopes that the research will lead to even smaller sensing technologies that would be built with single atoms or molecules.

Related sites

The Penner group's home page
The National Hydrogen Association
The Amazing Metal Sponge (a Web site about palladium)