carbon nanotube thread

Energy-harvesting nanotube thread can be sewn into clothing

Image credit: University of Texas

University of Texas researchers have developed a yarn woven from carbon nanotubes capable of producing an electrical current when stretched by human movement.

Thanks to the inconvenience of clunky batteries, researchers around the world are working hard on alternative ways to power our devices. Technologies such as a system to collect energy from the motion of hikers to store as electricity or an ultrathin harvesting system that extracts energy from a person’s movements to power gadgets are under development, although these are often impractical and inefficient.

A group of University of Texas nanoscientists took on the challenge, and have succeeded in creating energy-harvesting yarn which they say could have applications in smart textiles and wave power generation.

They began by spinning carbon nanotubes – tiny, hollow cylinders of carbon – into a “twistron” thread, using a similar method to that for standard wool fibres. During this process, the researchers were careful to create a structure with evenly distributed stress. The threads were then twisted to form a coil.

When this coil is stretched – much like a Slinky – the internal friction and strain within the structure causes electrical charge to be released from the carbon nanotubes. This charge was harvested by submerging the yarn into a salt solution, similar to seawater, which allows a current to flow to electrodes, and light up an LED.

At maximum strain, the yarn can provide 250W per kg: enough to power a speaker system or strimmer.

Having proved that their device worked in a laboratory, the team then tried placing their carbon nanotube yarn in the ocean off the coast of South Korea, attached to a floating balloon. They found that as the waves rolled, raising the balloon, the device generated electricity. By updating the device with a platinum electrode, they were able to make it resistant to corrosion by seawater.

The researchers were even able to incorporate the yarn into wearable fabrics by placing an electrolyte in a gel and using an uncoiled nanotube yarn as the electrode. When woven into a shirt, the device produced a current whenever the wearer breathed.

“Electronic textiles are of major commercial interest, but how are you going to power them?” said Professor Ray Baughman, director of the University of Texas’ NanoTech Institute. “Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries.”

According to the researchers, writing in Science, the yarn could be used in fashion fabric, but also in hardy wave power generators to be placed in oceans to generate clean energy.

“If our twistron harvesters could be made less expensively, they might ultimately be able to harvest the enormous amount of energy available from ocean waves. However, at present these harvesters are most suitable for powering sensors and sensor communications,” said Professor Baughman.

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