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Tiny detector finds hydrogen better

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12:41pm, October 9, 2001
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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.

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