Carbon Nanotube Yarns Unlock Low-Grade Waste Heat Energy Harvesting [Study]

Okayama University researchers have made carbon nanotube (CNT) yarns to get energy from low-grade waste heat efficiently.

This is a big step forward toward sustainable energy options.

(Photo: Wikimedia Commons/ Rao010384)

CNT Yarns to Take on Low-Grade Waste Heat

A new study in Small Methods describes this vital breakthrough. It provides a new way to turn waste heat into electrical energy, which could make industrial processes and everyday devices much more energy efficient.

Low-grade waste heat, below 200°C, has been hard to use as an energy source because thermoelectric materials aren't widespread. Most common thermoelectric materials are dangerous, expensive, or don't have the freedom needed for a wide range of uses, like making electronics you can wear.

A study group at Okayama University, led by Research Associate Professor Hiroo Suzuki, investigated how CNT yarns could be used for thermoelectric conversion to solve this problem.

CNT yarns, made of carbon nanotubes, seem like a good idea because they are bendable and can be used in fabric-based thermoelectric devices. However, one big problem is the lack of high-performance n-type CNT yarns (with too many electrons).

One way the researchers got around this problem was to use a new dopant called 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzimidazole-2-yl) phenyl) dimethylamine (N-DMBI) to make n-type CNT yarns that worked well.

New Methods for Doping and Processing: What This Means for IoT and Energy Harvesting

The researchers started by making CNT yarns using dry spinning. Next, they used a Joule annealing method to strengthen the yarns. In this process, an electric current is run through the material to control the high temperature, making the CNTs more crystallized and less thermally conductive.

This step is crucial for making the yarns better at thermoelectricity and mechanical features.

Next, the team improved the doping method by testing it with different solvents. They found that o-dichlorobenzene worked best for doping N-DMBI at low temperatures.

The improvements allowed n-doped CNT yarns to have very high thermoelectric power from 30°C to 200°C. The team also showed how these materials could be used by making a prototype π-type thermoelectric generator that could produce energy with a temperature difference of as little as 20°C.

Dr. Suzuki discussed the bigger implications of this research. He said that making power at low temperatures, even with small temperature differences, is very important for making thermoelectric modules that can use heat from many places, such as body heat, industrial waste heat, and even vehicle heat dissipation.

There are plenty of applications for this tech. Thermoelectric generators, for instance, can power local Internet of Things (IoT) gadgets like flexible health monitoring.

This novel concept might achieve better utilization of lost energy, which would address global energy issues and improve living conditions worldwide.

Complementary Advances in CNT Yarns

In addition to this study, Nara Institute of Science and Technology (NAIST) scientists have also made progress in making thermoelectric generators that can be worn. They made CNT yarns that quickly make electricity from body heat by aligning the bundles of CNTs and adding molecules that stop heat from escaping.

This work shows how valuable and flexible CNT yarns can be in many thermoelectric uses.

The NAIST team, led by Masakazu Nakamura, released a study in ACS Applied Nano Materials describing how to spread CNTs using glycerol and surfactants. This created CNT bundles that were very well aligned. This method improves the electrical and thermoelectric properties of CNT yarns. This makes them perfect for energy-harvesting devices that are made of stretchy fabrics.

Creating n-type CNT yarns that work well is a big step forward in energy gathering. These new ideas make it easier to turn low-grade waste heat into electricity, which leads to more environmentally friendly business practices and everyday uses.

As more studies are done to improve and expand the use of CNT yarns, the future of energy harvesting looks brighter and brighter, bringing new solutions to the world's energy problems.