Flexible thermoelectric generators could be a useful way to make carbon ‘green’ – ScienceDaily

Invisibly small carbon nanotubes lined up in the form of fibers and sewn into fabrics become a thermoelectric generator that can transform heat from the sun or other sources into other forms of energy.

The lab of physicist Junichiro Kono at Rice University led an effort with scientists from Tokyo Metropolitan University and the Rice-based Carbon Hub to fabricate custom nanotube fibers and test their potential for large-scale applications.

Their small-scale experiments led to a flexible, fiber-reinforced cotton fabric that transformed thermal energy into enough electrical energy to power an LED. With further development, they say these materials could become building blocks for fiber and textile electronics and energy harvesting.

The same nanotube fibers could also be used as heat sinks to actively cool sensitive electronic components with high efficiency.

An article on the project appears in Natural communications.

The effect seems simple: if one side of a thermoelectric material is hotter than the other, it produces usable energy. The heat can come from the sun or from other devices like the hotplates used in the fabric experiment. Conversely, adding energy can cause the material to cool on the hotter side.

So far, no macroscopic assembly of nanomaterials has displayed the “giant power factor,” about 14 milliwatts per square Kelvin meter, that Rice researchers have measured in carbon nanotube fibers.

“The power factor tells you how much power density you can get from a material with a certain temperature difference and a certain temperature gradient,” said Natsumi Komatsu, graduate student of Rice, and lead author of the article. She noted that a material’s power factor is a combined effect of its electrical conductivity and what’s known as the Seebeck coefficient, a measure of its ability to translate thermal differences into electricity.

“The ultra-high electrical conductivity of this fiber was one of the key attributes,” said Komatsu.

The source of this superpower also relates to the tuning of the Fermi energy inherent in nanotubes, a property that determines electrochemical potential. The researchers were able to control Fermi’s energy by chemically doping the nanotubes transformed into fibers by the Rice laboratory of co-author and chemical and biomolecular engineer Matteo Pasquali, allowing them to adjust the electronic properties of the fibers.

While the fibers they tested were cut into centimeters, Komatsu said there was no reason the devices couldn’t use the excellent nanotube fibers from the Pasquali lab that are coiled into continuous lengths. “No matter where you measure them, they have the same very high electrical conductivity,” she said. “The part I measured was small only because my installation is not capable of measuring 50 meters of fiber.”

Pasquali is director of the Carbon Hub, which promotes the expansion of the development of carbonaceous materials and hydrogen in a way that is also fundamentally changing the way the world uses fossil fuels.

“Carbon nanotube fibers are on a steady growth trajectory and are proving advantageous in more and more applications,” he said. “Rather than wasting carbon burning it for carbon dioxide, we can turn it into useful materials that have other environmental benefits in the production and transmission of electricity.”

Whether the new research leads to a solar panel you can throw in the washing machine remains to be seen, but Kono agreed the technology has great and varied potential.

“Nanotubes have been around for 30 years, and scientifically, we know a lot,” he said. “But to make real-world devices, we need macroscopically ordered or crystalline assemblies. These are the types of nanotube samples that Matteo’s group and my group can make, and there are many possible applications. . “

The co-authors of the article are Rice graduate students Oliver Dewey, Lauren Taylor and Mitchell Trafford and Geoff Wehmeyer, assistant professor of mechanical engineering; and Yota Ichinose, Professor Yohei Yomogida and Professor Kazuhiro Yanagi from Tokyo Metropolitan University.

Kono is Karl F. Hasselmann Professor of Engineering and Professor of Electrical and Computer Engineering, Physics and Astronomy, Materials Science and Nanoengineering. Pasquali is AJ Hartsook Professor of Chemical and Biomolecular Engineering and Professor of Chemistry, Materials Science and Nanoengineering.

The Department of Energy’s Basic Energy Sciences Program, the National Science Foundation, the Robert A. Welch Foundation, the Japan Society for the Promotion of Science, the US Air Force, and the Department of Defense have supported the research.

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