Thermoelectric (TE) materials convert heat into electricity and vice versa. The materials offer great potential for waste heat recovery and solid-state cooling.
In recent years, low-dimensional materials have recently attracted much interest as thermoelectric materials. Such materials have charge carrier confinement that enhances thermoelectric performance. One such material is a carbon nanotube. Because they are one-dimensional, flexible, and lightweight, carbon nanotubes are promising candidates.
However, preserving the significant power factor of individual carbon nanotubes in macroscopic assemblies has been challenging. Scientists at Rice University used tiny carbon nanotubes, aligned them as fibers, and sew them into fabrics. Their setup creates flexible thermoelectric generators that can convert heat or other sources into energy.
This is for the first time that macroscopic assemblies of nanomaterials have displayed the necessary ‘giant power factor,’ about 14 milliwatts per meter kelvin squared.
The carbon nanotubes that scientists used could also be used as heat sinks to cool sensitive electronics with high efficiency.
Rice graduate student Natsumi Komatsu, the lead author of the paper, said, “The power factor tells you how much power density you can get out of a material upon certain temperature difference and temperature gradient.”
“The ultrahigh electrical conductivity of this fiber was one of the key attributes.”
The effect seems simple: If one side of thermoelectric material is hotter than the other, it produces energy. The heat can come from the sun or other devices like the hotplates used in the fabric experiment. Conversely, adding energy can prompt the material to cool the hotter side.
The source of this superpower also relates to tuning the nanotubes’ inherent Fermi energy, a property that decides electrochemical potential. Scientists controlled the Fermi energy by chemically doping the nanotubes made into fibers. This enabled them to tune the fibers’ electronic properties.
Rice graduate student Natsumi Komatsu, the paper’s lead author, said, “While the fibers they tested were cut into centimeter lengths, there is no reason devices can’t make use of the excellent nanotube fibers from the Pasquali lab that are spooled in continuous 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 meters of fiber.”
Rice lab of co-author and chemical and biomolecular engineer Matteo Pasquali said, “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.”
“Nanotubes have been around for 30 years, and scientifically, a lot is known. But 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.”
- Komatsu, N., Ichinose, Y., Dewey, O.S. et al. Macroscopic wearable fibers of carbon nanotubes with giant thermoelectric power factor. Nat Commun 12, 4931 (2021). DOI: 10.1038/s41467-021-25208-z