Electrical Energy from Stretching Yarn

by Emil Morhardt

Well, yarn, sort of. This yarn is made by twisting carbon nanotubes until they become so twisted that the coil up into a helical spring-like configuration. You can do the same thing with cotton yarn or string. When the South Korean researchers (Kim et al., 2017) put the coil into an electrolyte then stretched it what they got was electrical current. Not a lot, but these are small laboratory-scale experiments and what the researchers had in mind was generating small amounts of energy to power sensors, for example, sewn into a shirt or gloves that are stretched and released under normal activities, but that wouldn’t work very well if the subject had to be immersed in an electrolyte. Or would it? They tried immersing the device, which they call a twistron, into the Gyeonpo Sea off South Korea where the temperature was 13ºC (a chilly 55ºF) and the sodium chloride content was 0.31 M, a nice electrolyte solution. But instead of sewing the yarn into a diver’s wetsuit, they attached it between a floating balloon and a sinker on the seabed to see if they could harvest ocean wave energy. Yes! They got it to light up a green LED whenever a wave came by.

And for clothing, they figured out how to incorporate the necessary electrolyte into the twistron by overcoating it with a gel electrolyte then insulated that with an ionically conducting hydrogel. When sewn into a shirt this acted on its own as a self-powered solid state strain sensor that worked for monitoring breathing.

But the goal that emerged was building a large-scale ocean energy harvester. The shirt thing sounds usable, but if they can make an ocean energy harvester out of their device, that would be terrific.

Kim, S.H., Haines, C.S., Li, N., Kim, K.J., Mun, T.J., Choi, C., Di, J., Oh, Y.J., Oviedo, J.P., Bykova, J., 2017. Harvesting electrical energy from carbon nanotube yarn twist. Science 357, 773-778.


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