A team of researchers—from the University of Texas and Hanyang University (South Korea)—have recently developed a type of carbon nanotube-based yarn that, they say, can produce electricity when you stretch it. This yarn is made up of carbon nanotubes which have been spun into a thread and twisted into a coil, like many other clothing threads. This thread, though, has internal structures that distribute stress evenly among each of the wrapped nanotubes. When you stretch the tubes, then, the strain and friction that creates, the tubes release a charge of electricity that can be harvested.
Nanotubes are, basically, very tiny, hollow cylinders of carbon—10,000 times smaller in diameter than the average human hair.
NanoTech Institute research scientist, Dr. Na Li explains, “Fundamentally, these yarns are supercapacitors.” The study co-lead author goes on to say, “In a normal capacitor, you use energy — like from a battery — to add charges to the capacitor. But in our case, 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.”
When you twist or stretch a harvester yarn, the carbon nanotube yarn volume decreases. This brings the electrical charges within the yarn closer together and that increases their potential energy. More potential energy means higher voltage contained in the charge that is stored within the yarn and that enables the harvesting of electricity from the yarn.
Specifically, stretching or coiling of the yarn at rate of 30 times per second is capable of generating about 250 watts per kilogram of peak electrical power.
Study co-author Dr. Ray Baughman is the director of the NanoTech Institute. he comments, “Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second.”
Baughman adds, “Electronic textiles are of major commercial interest, but how are you going to power them? Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries. Our yarns produced over a hundred times higher electrical power per weight when stretched compared to other weavable fibers reported in the literature.”