Tiny detector finds hydrogen better. (Materials Science).

Researchers have made a miniature device that can quickly detect hydrogen leaks. Such a device might be useful in future cars powered by fuel cells since hydrogen concentrations above a few percent can be explosive. The same device also could be useful for regulating hydrogen concentrations in the cars' engines.

Most hydrogen sensors rely on thin palladium wires, which decrease their conductivity within seconds or minutes after adsorbing molecules of the gas. Reginald M. Penner of the University of California at Irvine and his colleagues suspected that sensors made with much smaller wires would operate in the same way but more quickly.

In their experiments, tiny arrays of 10 to 200 palladium wires--each with a diameter of 100 to 300 nanometers--detected hydrogen in as little as 20 to 80 milliseconds. Unlike conventional sensors' wires, however, the wires of the new sensor became more conductive in the presence of hydrogen, says Penner, whose team reports its results in the Sept. 21 SCIENCE.

Penner learned that the superthin wires work in an entirely new way. After they're exposed to and removed from hydrogen once, they develop tiny cracks that reduce conductivity. Subsequent exposure to gas containing as little as 0.5 percent hydrogen makes the wires swell again, reestablishing connections.

The device requires very little power, says Penner, who envisions a tiny hydrogen alarm that could be worn as a lapel pin. --J.G.