26 AUG 2017
A twisted fibre made of gel-coated carbon nanotubes could be the very thing we need to steal energy from our surroundings that would otherwise go to waste.
Threads of a material dubbed “twistron” have already shown incredible promise in the laboratory, but could one day be built into power harvesters that collect the energy equivalent of spare change from our bodies, furniture, or wider environment.
“The easiest way to think of twistron harvesters is, you have a piece of yarn, you stretch it, and out comes electricity,” says Carter Haines from The University of Texas at Dallas, whose international team of researchers developed the technology.
It’s little wonder why we’re obsessed with the idea – our world buzzes with low level electromagnetic waves, friction, and temperature gradients that can be tapped into and used to shuffle around a few electrons.
But for all of their variety, the hunt is still on to make a material that can harvest that energy, and is as robust, cheap, versatile, and efficient as possible.
The twistron might not be the final answer, but it’s certainly showing promise.
The mechanism responsible for the fibre’s generation of electricity is surprisingly simple. A mesh of carbon atoms rolled into tubes 10,000 times thinner than the width of a human hair makes up the fundamental fibres of the complete filament.
Bundles of these long carbon nanotubes are woven together and twisted, making them elastic. Imagine over-winding a piece of string, which can then be stretched and relaxed as the twists pull back on themselves.
When coated in an electrolyte solution – something as simple as salt water, for example – the changing shape of the fibre moves the carbon-nanotubes around, rearranging charges to generate a voltage.
“Fundamentally, these yarns are supercapacitors,” says researcher Na Li.
“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.”
The charge generated by stretching the thread is impressive considering it’s basically a length of carbon string.
If you can get a kilogram (about 2.2 pounds) of the stuff to buzz at a rate of 30 times a second you’ll be sparking a generous 250 watts of electricity. More than enough to run a desktop computer and perhaps a small heater.
Of course there are plenty of more efficient ways to generate this kind of charge, but tethering the material to something already moving, such as clothing, could provide easy access to energy in places where batteries or solar power aren’t convenient.
“There is a lot of interest in using waste energy to power the Internet of Things, such as arrays of distributed sensors,” says Li.
As a proof of concept, the researchers sewed twistron into a shirt, and found normal breathing was enough to produce a charge.
Cranking it up a notch, they attached a thin, 10-centimetre (4-inch) long thread to a balloon and a sinker, and measured its change in voltage as it experienced the rise and fall of waves at a rate of about one every second.
The output was 1.79 microwatts of electricity; not bad for barely a milligram of fibre dangling from a balloon.
“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,” says researcher Ray Baughman.
Even in small amounts, the carbon nanotube harvesters could conceivably pull sufficient power for free-floating ocean probes to beam communications back to reporting stations.
Right now production isn’t simple or cheap, meaning the technology still has some way to go before it ticks all the boxes.
But carbon nanotube technology is showing wide promise in many different fields, so who knows? Maybe one day in the not-too-distant future you’ll be charging up your smart phone by busting out some lush moves in your shiny new twistron suit.