High-tech yarns generate electricity when stretched or twisted

Source:Xinhua Published: 2017/8/27 10:08:24

Scientists from the US, South Korea and China have developed high-tech yarns that generate electricity when stretched or twisted, an achievement they believed could eventually help curb the use of fossil fuels blamed for global warming. 

In a study published this week in the US journal Science, the researchers reported stretching their yarns, called twistron, 30 times a second, and generated 250 watts per kilogram of peak electrical power, which is about 100 times higher than that of other wearable fibers reported in the literature 

In the lab, the researchers showed that a twistron yarn weighing less than a housefly could power a small LED, which lit up each time the yarn was stretched. 

"Just stretch it, and out comes electricity directly," said co-lead author Na Li, a research scientist in the Alan G. MacDiarmid NanoTech Institute at the University of Texas at Dallas. 

Li said their yarns are constructed from carbon nanotubes, which are hollow cylinders of carbon 10,000 times smaller in diameter than a human hair. 

To generate electricity, the yarns must first be either submerged in or coated with an ionically conducting material, or electrolyte, which can be as simple as a mixture of ordinary table salt and water. 

"When you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed," she said. 

When a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy, Li explained. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity. 

Li said the yarns are most suitable for powering sensors for the Internet of Things, where "changing batteries is impractical." 

"Based on demonstrated average power output, just 31 milligrams of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a two-kilobyte packet of data over a 100-meter radius every 10 seconds for the Internet of Things," she said. 

The researchers also showed when sewed into a shirt, the yarns have the potential to serve as a self-powered respiration sensor. 

In addition, a proof-of-concept demonstration showed that a 10-centimeter-long yarn attached between a balloon and a sinker that rested on the seabed off the east coast of South Korea produced measured electricity from ocean waves every time they stretched the yarn. 

"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," said Ray Baughman, director of the NanoTech Institute and a corresponding author of the study. 

The article also included researchers from Virginia Tech, Wright-Patterson Air Force Base, Hanyang University in South Korea and Nankai University in China.



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