Rensselaer Research Review Winter 2010-11
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* Graphene foam

Photo Credit: Rensselaer/Nikhil Koratkar

Results of the study show the new graphene foam structure detected ammonia at 1,000 parts-per-million in 5 to 10 minutes at room temperature and atmospheric pressure. The accompanying change in the graphene’s electrical resistance was about 30 percent. This compared favorably to commercially available conducting polymer sensors, which undergo a 30 percent resistance change in 5 to 10 minutes when exposed to 10,000 parts-per-million of ammonia. In the same time frame and with the same change in resistance, the graphene foam detector was 10 times as sensitive. The graphene foam detector’s sensitivity is effective down to 20 parts-per-million, much lower than the commercially available devices. Additionally, many of the commercially available devices require high power consumption since they provide adequate sensitivity only at high temperatures, whereas the graphene foam detector operates at room temperature.

Koratkar’s team used nitrogen dioxide as the second test gas. Different explosives including nitrocellulose gradually degrade, and are known to produce nitrogen dioxide gas as a byproduct. As a result, nitrogen dioxide also is used as a marker when testing for explosives. Additionally, nitrogen dioxide is a common pollutant found in combustion and auto emissions. Many different environmental monitoring systems feature real-time nitrogen dioxide detection.

The new graphene foam sensor detected nitrogen dioxide at 100 parts-per-million by a 10 percent resistance change in 5 to 10 minutes at room temperature and atmospheric pressure. It showed to be 10 times more sensitive than commercial conducting polymer sensors, which typically detect nitrogen dioxide at 1,000 part-per-million in the same time and with the same resistance chance at room temperature. Other nitrogen dioxide detectors available today require high power consumption and high temperatures to provide adequate sensitivity. The graphene foam sensor can detect nitrogen dioxide down to 20 parts-per-million at room temperature.

First Practical Nanostructure-Based Gas Detector

“We see this as the first practical nanostructure-based gas detector that’s viable for commercialization,” said Koratkar, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer. “Our results show the graphene foam is able to detect ammonia and nitrogen dioxide at a concentration that is an order of magnitude lower than commercial gas detectors on the market today.”

The graphene foam can be engineered to detect many different gases beyond ammonia and nitrogen dioxide, he said.

Studies have shown the electrical conductivity of an individual nanotube, nanowire, or graphene sheet is acutely sensitive to gas adsorbtion. But the small size of individual nanostructures made it costly and challenging to develop into a device, plus the structures are delicate and often don’t yield consistent results.

* Graphene foam

Photo Credit: Rensselaer/Nikhil Koratkar

The new graphene foam gas sensor overcomes these challenges. It is easy to handle and manipulate because of its large, macroscale size. The sensor also is flexible, rugged, and robust enough to handle wear and tear inside of a device. Plus it is fully reversible, and the results it provides are consistent and repeatable. Most important, the graphene foam is highly sensitive, thanks to its 3-D, porous structure that allows gases to easily adsorb to its huge surface area. Despite its large size, the graphene foam structure essentially functions as a single nanostructure. There are no breaks in the graphene network, which means there are no interfaces to overcome, and electrons flow freely with little resistance. This adds to the foam’s sensitivity to gases.

“In a sense we have overcome the Achilles’ heel of nanotechnology for chemical sensing,” Koratkar said. “A single nanostructure works great, but doesn’t mean much when applied in a real device in the real world. When you try to scale it up to macroscale proportions, the interfaces defeats what you’re trying to accomplish, as the nanostructure’s properties are dominated by interfaces. Now we’re able to scale up graphene in a way that the interfaces are not present. This allows us to take advantage of the intrinsic properties of the nanostructure, yet work with a macroscopic structure that gives us repeatability, reliability, and robustness, but shows similar sensitivity to gas adsorbtion as a single nanostructure.”

Along with Koratkar, co-authors of the paper are: Rensselaer graduate students Fazel Yavari and Abhay Varghese Thomas; along with professors W.C. Ren, H.M. Cheng and graduate student Z.P. Chen of the Shenyang National Laboratory for Materials Science at the Chinese Academy of Sciences.

This research was supported in part by the Advanced Energy Consortium (AEC), the National Science Foundation of China, and the Chinese Academy of Sciences.

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