A team of Stanford researchers including EE Professor Eric Pop report the design and fabrication of single-wall carbon nanotube thermoelectric devices on flexible polyimide substrates as a basis for wearable energy converters.

source: ScienceDaily.com [...]
Inspiration came from a desire to ultimately fabricate energy converting devices from the same materials as the active devices themselves, so they can blend in as an integral part of the total system. Today, many biomedical nanodevices' power supplies come from several types of batteries that must be separated from the active portion of the systems, which is not ideal.

In Applied Physics Letters, the researchers report the design and fabrication of single-wall carbon nanotube thermoelectric devices on flexible polyimide substrates as a basis for wearable energy converters.

"Carbon nanotubes are one-dimensional materials, known for good thermoelectric properties, which mean developing a voltage across them in a temperature gradient," said Professor Eric Pop. "The challenge is that carbon nanotubes also have high thermal conductivity, meaning it's difficult to maintain a thermal gradient across them, and they have been hard to assemble them into thermoelectric generators at low cost."

The group uses printed carbon nanotube networks to tackle both challenges.

Professor Pop continued, "For example, carbon nanotube spaghetti networks have much lower thermal conductivity than carbon nanotubes taken alone, due to the presence of junctions in the networks, which block heat flow. Also, direct printing such carbon nanotube networks can significantly reduce their cost when they are scaled up."

Thermoelectric devices generate electric power locally "by reusing waste heat from personal devices, appliances, vehicles, commercial and industrial processes, computer servers, time-varying solar illumination, and even the human body," said Hye Ryoung Lee, lead author and a research scientist.

"To eliminate hindrances to large-scale application of thermoelectric materials – toxicity, materials scarcity, mechanical brittleness – carbon nanotubes offer an excellent alternative to other commonly used materials," Lee said.

The group's approach demonstrates a path to using carbon nanotubes with printable electrodes on flexible polymer substrates in a process anticipated to be economical for large-volume manufacturing. It is also "greener" than other processes, because water is used as the solvent and additional dopants are avoided.

Excerpted from "Nontoxic, flexible energy converters could power wearable devices" April 27, 2021