Aug 17 2021Reviewed by Alex Smith

Invisibly minute carbon nanotubes, drawn as fibers and sewn into fabrics, turn out to be a thermoelectric generator that can convert heat from the sun or other sources into energy.

Physicist Junichiro Kono from Rice University laboratory guided a team of scientists at Tokyo Metropolitan University (TMU) and the Rice-based Carbon Hub to develop tailored nanotubes and test their potential for large-scale applications.

The small-scale experiments of the researchers resulted in a fiber-improvised, flexible cotton fabric that converted heat into required energy to power an LED. Further improvements will enable the materials to form building blocks for fiber and textile electronics and energy harvesting. The same nanotube fibers can find application as heat sinks to actively cool sensitive devices with greater efficiency.

The study has been published in the journal Nature Communications.

The effect looked to be simple, where, if one side of thermoelectric material is hotter compared to the other, it generates energy. The heat may arrive from the Sun or other devices such as the hotplates that are employed in the fabric experiment. In another way, adding energy can encourage the material to cool the hotter side.

So far, macroplastic assemblies of nanomaterials have not displayed the required, “giant power factor” of around 14 mW/mK². This is the value quantified by the Rice researchers in carbon nanotube fibers.

The power factor tells you how much power density you can get out of a material upon certain temperature difference and temperature gradient.

Natsumi Komatsu, Study Lead Author and Graduate Student, Rice University

According to Komatsu, the power factor of a material is a joint effect achieved from its electrical conductivity and Seebeck coefficient, which is a measure of its potential to convert thermal differences into electricity.

“The ultrahigh electrical conductivity of this fiber was one of the key attributes,” added Komatsu. The source of this superpower also links to tuning the inherent Fermi energy of the nanotubes, which is a characteristic that determines the electrochemical potential.

The scientists were able to regulate the Fermi energy by chemically doping the nanotubes turned into fibers by the Rice University laboratory associated with Matteo Pasquali, who is the co-author and a chemical and biomolecular engineer, enabling the researchers to tune the electronic properties of the fibers.

While the tested fibers were cut into centimeter lengths, Komatsu stated that there is no evidence to suggest that the devices cannot utilize the exceptional nanotube fibers from the Pasquali laboratory that are spooled in constant lengths.

No matter where you measure them, they have the same very high electrical conductivity. The piece I measured was small only because my setup isn’t capable of measuring 50 m of fiber.

Natsumi Komatsu, Study Lead Author and Graduate Student, Rice University

Pasquali is the director of the Carbon Hub, which encourages expanding the enhancement of hydrogen and carbon materials in a way that also basically alters the global usage methods of fossil hydrocarbons.

Carbon nanotube fibers have been on a steady growth path and are proving advantageous in more and more applications. Rather than wasting carbon by burning it into carbon dioxide, we can fix it as useful materials that have further environmental benefits in electricity generation and transportation.

Matteo Pasquali, Study Co-Author and Chemical and Bio-Molecular Engineer, Rice University

Whether the new study results in a solar panel that people can dump in the washing machine remains to be seen, but Kono agreed the technology has huge and varied capabilities.

“Nanotubes have been around for 30 years, and scientifically, a lot is known. But in order to make real-world devices, we need macroscopically ordered or crystalline assemblies. Those are the types of nanotube samples that Matteo’s group and my group can make, and there are many, many possibilities for applications,” stated Pasquali.

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

Kono is the Karl F. Hasselmann Professor in Engineering and a professor of electrical and computer engineering, physics and astronomy and materials science and nanoengineering. Pasquali is the A.J. Hartsook Professor of Chemical and Biomolecular Engineering and a professor of chemistry and materials science and nanoengineering.

This study was financially supported by the Department of Energy Basic Energy Science program, the National Science Foundation, the Robert A. Welch Foundation, the Japan Society for the Promotion of Science, and the U.S. Air Force, and the Department of Defense.

Woven nanotubes make a thermoelectric generator. Video Credit: Rice University.

Komatsu, N., et al. (2021) Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor. Nature Communications. doi.org/10.1038/s41467-021-25208-z.

Source: https://www.rice.edu/