By Josh Perry, Editor
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Researchers from Rice University (Houston, Texas) demonstrated that laser-induced graphene (LIG) can be incorporated into metal-free devices that generate static electricity to power wearable electronics, according to a report from the school.

Rice University postdoctoral researcher Michael Stanford holds a flip-flop with a triboelectric nanogenerator, based on laser-induced graphene, attached to the heel.
(Jeff Fitlow/Rice University)

“In experiments, the researchers connected a folded strip of LIG to a string of light-emitting diodes and found that tapping the strip produced enough energy to make them flash,” the article explained. “A larger piece of LIG embedded within a flip-flop let a wearer generate energy with every step, as the graphene composite’s repeated contact with skin produced a current to charge a small capacitor.”

LIG is created by heating chemicals on the surface of a polymer with a laser and researchers took that material and created electrodes to test their ability to produce electricity. The best results came from materials on opposite ends of the triboelectric series, which defines the ability of a material to produce static electricity through contact.

“In the folding configuration, LIG from the tribo-negative polyimide was sprayed with a protecting coating of polyurethane, which also served as a tribo-positive material,” the article continued. “When the electrodes were brought together, electrons transferred to the polyimide from the polyurethane. Subsequent contact and separation drove charges that could be stored through an external circuit to rebalance the built-up static charge. The folding LIG generated about 1 kilovolt, and remained stable after 5,000 bending cycles.”

The best configuration was able to produce voltages above 3.5 kilovolts and power of more than eight milliwatts. In the flip-flop, the generator stored 0.22 millijoules of electricity after a one-kilometer walk.

The research was recently published in ACS Nano. The abstract read:

“Triboelectric nanogenerators (TENGs) show exceptional promise for converting wasted mechanical energy into electrical energy. This study investigates the use of laser-induced graphene (LIG) composites as an exciting class of triboelectric materials in TENGs. Infrared laser irradiation is used to convert the surfaces of the two carbon sources, polyimide (PI) and cork, into LIG.

“This gives the bilayer composite films the high conductivity associated with LIG and the triboelectric properties of the carbon source. A LIG/PI composite is used to fabricate TENGs based on conductor-to-dielectric and metal-free dielectric-to-dielectric device geometries with open-circuit voltages >3.5 kV and peak power >8 mW.

“Additionally, a single sheet of PI is converted to a metal-free foldable TENG. The LIG is also embedded within a PDMS matrix to form a single-electrode LIG/PDMS composite TENG. This single-electrode TENG is highly flexible and stretchable and was used to generate power from mechanical contact with skin.

“The LIG composites present a class of triboelectric materials that can be made from naturally occurring and synthetic carbon sources.”

See the new generator work in the video below: