Scientists have made custom nanotube fibers and tested their potential for large-scale applications. The small-scale experiments led to a fiber-enhanced, flexible cotton fabric that turns heat into enough energy to power an LED. With further development, such 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 electronics with high efficiency.
The effect seems simple: If one side of a 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.
Until now, no macroscopic assemblies of nanomaterials have displayed the necessary “giant power factor” — about 14 milliwatts per meter kelvin squared — that the researchers measured in carbon nanotube fibers. A material’s power factor is a combined effect from its electrical conductivity and what’s known as the Seebeck coefficient, a measure of its ability to translate thermal differences into electricity.
The source of this power also relates to tuning the nanotubes’ inherent Fermi energy, a property that determines electrochemical potential. The researchers were able to control the Fermi energy by chemically doping the nanotubes made into fibers, allowing them to tune the fibers’ electronic properties. While the fibers they tested were cut into centimeter lengths, devices can make use of the nanotube fibers that are spooled in continuous lengths.