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Flexible And Wearable Electrical Generators Just Became A Lot More Practical

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Rice University postdoctoral researcher Michael Stanford holding a flip-flop with a triboelectric nanogenerator attached on it. During experiments, Stanford and colleagues found that the device stored 0.22 millijoules after a 1-kilometer walk.   ( Jeff Fitlow | Rice University )

In a new study, researchers created a metal-free device that generates electricity when it comes in contact with other surfaces, including human skin.

The team used a material called laser-induced graphene or LIG — a flaky foam of carbon created when chemicals are heated in the surface of polymer using laser. They adapted LIG into smaller devices that produce static electricity to power electronics.

The device, the researchers believe, can make wearable tech that harvest energy more practical. Details were published in the journal ACS Nano.

Developing Flexible Generators

The devices rely on something called triboelectric effect by which materials become electrically charged when they come in contact with another material. When materials are put together and then pulled apart, they build charges that can be channeled toward power generation.

In their experiments, researchers at Rice University connected a folded strip of LIG to a string of light-emitting diodes. They reported that by simply tapping the strips, they produced enough energy to produce flashes of light.

In another experiment, the team attached a larger piece of LIG on a flip-flop. They hoped that, by simply walking — through repeated contact between LIG and the wearer's ankle — the graphene composite would produce enough current to charge a small capacitor.

How Daily Activities Could Generate Power That Charge Electronic Devices

The researchers envision future wearable devices that can generate a charge from simple and everyday movements.

"This could be a way to recharge small devices just by using the excess energy of heel strikes during walking, or swinging arm movements against the torso," stated James Tour, a chemist at Rice University and one of the authors of the study. Tour was also involved in a previous study that produced LIG in 2014.

They reported that the best configurations produced voltages of above 3.5 kilovolts and more than 8 milliwatts in peak power.

"The nanogenerator embedded within a flip-flop was able to store 0.22 millijoules of electrical energy on a capacitor after a 1-kilometer walk," added Michael Stanford, lead author of the paper and a postdoctoral researcher at Rice University. "This rate of energy storage is enough to power wearable sensors and electronics with human movement."

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