Nanotechnology Helps Scientists Make Bendy Sensors for Hydrogen Vehicles
16 Aug, 2007 11:51 am
Flexible hydrogen sensors and sensor arrays (i.e., sensory skins) can be used in a wide of range of systems which require demanding low cost, large area, light weight, mechanical flexibility and mechanical shock resistance.
Scientists at the U.S. Department of Energy's Argonne National Laboratory have used their insights into nanomaterials to create bendy hydrogen sensors and sensory skins, which are at the heart of hydrogen fuel cells.
The driving force for us to develop low-cost, high-performance hydrogen sensors was the Department of Energy’s Energy Hydrogen Program which is making progress towards the goal of a 2015 commercialization decision. In the program, fast and precise detection of leakage of hydrogen is critical to ensure the safe use of hydrogen technologies in realizing a “hydrogen economy.” Therefore, hydrogen sensors represent one of the core technologies in the program. As one of the best national laboratories of DOE, Argonne has the opportunity to propel the research pace in this field.
In comparison to previously designed hydrogen sensors, which are rigid and use expensive, pure palladium, the new sensors are flexible and use single-walled carbon nanotubes (SWNTs) to improve efficiency and reduce cost. 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.
Yugang Sun and H. Hau Wang, researchers in Argonne's Center for Nanoscale Materials and Materials Science Division, respectively, fabricated the new sensing devices using a two-step process separated by high and low temperatures. First, at around 900 degrees C, researchers grow SWNTs on a silicon substrate using chemical vapor deposition. Then, researchers transfer the SWNTs onto a plastic substrate at temperatures lower than 150 degrees C using a technique called dry transfer printing.
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 play 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.
According to Sun, these sensors exhibit excellent sensing performance in terms of high sensitivity, fast response time and quick recovery, and the use of plastic sheets reduces their overall weight and increases their mechanical flexibility and shock resistance. The sensors are also able to be wrapped around curved surfaces, and this proves useful in many applications, notably in vehicles, aircraft and portable electronics.
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 3 seconds. Even after bending—with a bending radius of approximately 7.5 mm—and relaxing 2,000 times, the devices still perform with as much effectiveness.
The next stage of research will involve scaling up the fabrication strategy to make large-area sensor arrays.
Sun, Yugang. Applied Physics Letters. 90, 213107 (2007)