Bendy HFC Sensors Created
ARGONNE, Ill., Aug. 1, 2007 -- Nanodevices have been fabricated to create bendy hydrogen sensors, which are at the heart of hydrogen fuel cells (HFCs) used in hydrogen vehicles.
The promise of vehicles that use hydrogen fuel cells is intriguing, but experts have said several technology problems must be resolved before they are more than a novelty.
A flexible hydrogen sensor fabricated from nanodevices. (Image courtesy Argonne National Laboratory)
Yugang Sun and H. Hau Wang, researchers at the US Department of Energy's Argonne National Laboratory Center for Nanoscale Materials and Materials Science Div., fabricated the new sensing devices using a two-step process separated by high and low temperatures. First they grow SWNTs on a silicon substrate using chemical vapor deposition, at around 900 °C; they then they transfer the SWNTs onto a plastic substrate using dry-transfer printing at lower than 150 °C.
Compared to typical hydrogen sensors, which are rigid and use expensive, pure palladium, the new sensors are bendy and use single-walled carbon nanotubes (SWNTs) to improve efficiency and lower costs.
This precise process is what allows the film of nanotubes to form on the plastic, after which the palladium nanoparticles can be deposited on the SWNTs to make the sensors. The palladium nanoparticles have an important role in increasing the interaction between hydrogen and the SWNTs to enhance the change of resistance of the device when it is exposed to hydrogen molecules.
Sun said the sensors exhibit excellent performance in terms of high sensitivity, fast response time and quick recovery, and that the use of plastic sheets reduces their overall weight and increases their mechanical flexibility and shock resistance. The sensors can also be wrapped around curved surfaces, which is useful in many applications, notably in vehicles, aircraft and portable electronics.
“The leakage of hydrogen caused by tiny pinholes in the pipe of a space shuttle, for example, could not be easily detected by individual rigid detectors because the locations of pinholes are not predetermined,” Sun said. “However, laminating a dense array of flexible sensors on the surfaces of the pipe can detect any hydrogen leakage prior to diffusion to alert control units to take action.”
Flexible hydrogen sensors show a change of 75 percent in their resistance when exposed to hydrogen at a concentration of 0.05 percent in air. The devices can detect the presence of 1 percent hydrogen at room temperature in three seconds. Even after bending -- with a bending radius of approximately 7.5 mm -- and relaxing 2000 times, the devices still perform with as much effectiveness.
"The development of these hydrogen sensors will help to ensure economical, environmental and societal safety, as the nation is realizing the potential for a more hydrogen-based economy," Argonne said in a statement.
For more information, visit: www.anl.gov
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