Rice University researchers designed a wearable device that harvest energy from movement.
The researchers led by James Tour designed laser-induced graphene (LIG) into devices free from metals to produce electricity. This phenomenon is similar to rubbing a balloon on hair as this connects LIG composites with other surfaces that produce static electricity that powers devices.
The principle that works behind materials gathering a charge through contact is called the triboelectric effect. There is an occurrence of a build-up of surface charge when materials combine and separate that could be used to generate power.
A LIG-folded strip was connected to a string of light-emitting diodes. This set-up allowed enough energy to be produced by tapping that made them flash. The researchers were able to generate an embedded LIG piece within a flip-flop enough energy as the wearer moves with every step. Current enough to charge was produced due to the repeated contact of the graphene composite with skin.
"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," Tour said.
Heating chemicals through a laser on the surface of a polymer or other material produces LIG, a graphene foam. This leaves only interconnected flakes of two-dimensional carbon. The researchers utilized common polyamide to create LIG. However, this was extended to paper, wood, food, and plants. Their findings were published in the American Chemical Society journal ACS Nano.
Different materials such as polyamide and cork were tested for their capacity to produce energy and quality. Materials on the opposite ends of the triboelectric series produced the best results were and were quantified in terms of the capacity to generate a static charge by contact electrification.
Polyurethane, a tribo-positive material, was sprayed on LIG from the tribo-negative polyamide. Electrons moved from the polyurethane to the polyamide when the electrodes were coupled together. Charges were built through contact and separation of these electrodes. An estimated 1 kilovolt was produced by the folding LIG, which remained stable after 5, 000 bending cycles.
"The best configuration, with electrodes of the polyimide-LIG composite and aluminum, produced voltages above 3.5 kilovolts with a peak power of more than 8 milli Watts," according to Phys.
"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," said Rice postdoctoral researcher Michael Stanford, lead author of the paper. "This rate of energy storage is enough to power wearable sensors and electronics with human movement."
