Carbon Nanotube Spaghetti Proves Perfect for Flexible, Wearable Energy-Harvesting Generators

A team of researchers from Stanford University has published a paper detailing non-toxic, flexible energy-harvesting devices which they say could power future wearable electronics — thanks to carbon nanotube spaghetti.

"Carbon nanotubes are one-dimensional materials, known for good thermoelectric properties, which mean developing a voltage across them in a temperature gradient," explains Professor Eric Pop of the material focused upon in the paper. "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 solution: Carbon nanotube networks. "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," Pop says. "Also, direct printing such carbon nanotube networks can significantly reduce their cost when they are scaled up."

Using direct-printed carbon nanotube spaghetti networks, the team were able to develop non-toxic, flexible, and environmentally-friendly thermoelectric generators — capable of harvesting energy from the wearer's body heat and either storing it in a battery or capacitor or directly powering worn electronics.

"[We] recycle energy as much as we can, converting uneven heat distribution to electrical energy for use for the next cycle of operation, which we demonstrated by using non-toxic nanotube-based thermoelectric generation," notes Professor Yoshio Nishi of the work. "This concept is in full alliance with the world's goal of reducing our total energy consumption."

"Traditional thermoelectrics that rely on bismuth telluride are brittle and stiff, with limited applications," adds Pop. "Carbon-based thermoelectrics are also more environmentally friendly than those based on rare or toxic materials like bismuth and tellurium."

The team's work has been published under open-access terms in the journal AIP Applied Physics Letters.