NTU Singapore researchers have created a stretchy and waterproof “fabric” that converts energy generated by human motions into electrical energy. A polymer is a key component in the fabric because it turns mechanical stress into electrical energy when pushed or compressed. It’s also created with a base layer of elastic spandex and a rubber-like substance to make it sturdy, flexible, and waterproof. The NTU Singapore team demonstrated that tapping on a 3cm by 4cm patch of the novel fabric generated enough electrical energy to light up 100 LEDs in a proof-of-concept experiment published in the scientific journal Advanced Materials in April. The cloth did not degrade in performance whether washed, folded, or crumpled, and it could sustain a constant electrical output for up to five months.
The study’s lead author, the materials scientist and NTU Associate Provost Professor Lee Pooi See, said: “Many attempts have been made to create fabric or garments that can harvest energy from movement, but one of the most difficult challenges has been to create something that does not degrade in function after being washed while maintaining excellent electrical output. In our research, we showed that our prototype still works after being washed and crumpled. We believe it might be weaved into t-shirts or built into the soles of shoes to capture energy from the body’s slightest motions and pipe it to mobile devices.”
Harvesting an alternative source of energy
The NTU team’s electricity-generating fabric is an energy collecting technology that converts vibrations produced by even the tiniest bodily motions into power. When the prototype fabric is crushed or squished (piezoelectricity), and when it comes into touch or is in friction with other materials, such as skin or rubber gloves, it creates electricity in two ways (triboelectric effect). To develop the prototype, the researchers first created a stretchy electrode by screenprinting silver and styrene-ethylene-butylene-styrene (SEBS), a rubber-like substance found in teethers and bike grips, to make it more flexible and waterproof.
This flexible electrode is then attached to a piece of nanofibre fabric composed of two major components: poly(vinylidene fluoride)-co-hexafluoropropylene, a polymer that generates an electrical charge when compressed, bent, or stretched, and lead-free perovskites, a promising material in the field of solar cells and LEDs.
Jiang Feng, an NTU Ph.D. student on the study team, explained: “The incorporation of perovskites into PVDF-HPF improves the prototype’s electrical output. As a more ecologically benign choice, we used lead-free perovskites in our investigation. While perovskites are naturally brittle, incorporating them into PVDF-HPF offers them outstanding mechanical endurance and flexibility. The PVDF-HPF also functions as an additional layer of protection for the perovskites, increasing their mechanical properties and stability.”
The end result is a prototype fabric that generates 2.34 watts per square meter of electricity—enough to run tiny electrical devices like LEDs and commercial capacitors. Proof of concept The NTU scientists demonstrated how a hand tapping on a 3cm by 4cm piece of cloth constantly could light up 100 LEDs or charge different capacitors, which are devices that store electrical energy and are present in gadgets such as mobile phones. The cloth demonstrated good durability and stability—its electrical qualities did not diminish after washing, folding, and crumpling.
It also produced a consistent electrical output for the next five months. By attaching their fabric to the arm, leg, hand, and elbow, as well as the insoles 3 of shoes, the researchers demonstrated that it could collect energy from a variety of human movements while having no effect on the movements. “Despite greater battery capacity and lower power demand, power sources for wearable devices still necessitate regular battery changes,” Prof. Lee explained. Our findings reveal that our vibration-harvesting prototype fabric might possibly improve the life of a battery or even be used to create self-powered devices by harvesting vibration energy from a human being. To our knowledge, this is the first hybrid perovskite-based energy device that is stable, stretchy, breathable, waterproof, and capable of generating exceptional electrical output performance. The NTU team’s body of work looks at how energy created in the environment might be scavenged, and our fabric-based energy collecting prototype expands on that. For example, the team recently created a form of film that could be put on roofs or walls to capture the energy generated by wind or rain falling on them. The researchers are currently investigating how the same cloth may be used to gather various types of energy.
