Scientists at NTU Singapore have developed stretchable & waterproof “fabric” that converts the energy generated by body movements into electrical energy.
A crucial component in fabric is a polymer that, when pressed or squeezed, converts mechanical stress into electrical energy. It’s also made with stretchy spandex as a base layer and is integrated with a rubber-like material to keep it strong, flexible & waterproof.
In a proof-of-concept experiment published in April in the scientific journal Advanced Materials, the NTU Singapore team showed that tapping on a 3 x 4 cm piece of the new fabric generates enough electrical energy to light-up 100 LEDs .
Washing, folding & crumpling of the fabric did not cause performance degradation, and it could maintain stable electrical output for up to 5 months.
Lee Pooi See, materials scientist and associate provost (postgraduate education) at NTU, who led the study, said: “There have been many attempts to develop fabrics or garments that can harvest energy from movement, but a major challenge has been to make something that does not degrade after washing, and at same time retains excellent electrical output. In our study, we show that our prototype still works well after washing & crumpling. We think it could be woven into T-shirts or integrate into the soles of shoes to collect energy from the body’s smallest movements and send power to mobile devices.”
Harvesting an alternative source of energy
The electricity-generating substance developed by the NTU team is an energy-harvesting device that converts the vibrations generated by the smallest body movements in everyday life into electricity. The prototype fabric generates electricity in two ways: when it is pressed or squashed (piezoelectricity), and when it comes in-to contact or is in friction with other materials such as skin or rubber gloves (triboelectric effect).
To fabricate the prototype, scientists first made a stretchable electrode by screen-printing an “ink” of silver and styrene ethylene butylene styrene (SEBS), a rubber-like material found in teethers & handlebar grips, to make it more stretchy & to make it more waterproof. This stretchable electrode is then attached to a piece of nanofiber fabric made up of 2 main components: Poly(vinylidene fluoride)-co-hexafluoropropylene (PVDFHPF), a polymer that generates an electrical charge when compressed, bent, or stretched; and lead-free perovskites, a promising material in field of solar cells & LEDs.
NTU Ph.D. Student Jiang Feng, who is part of the research team, explains: “Embedding perovskites in PVDF-HPF increases the electrical output of the prototype. In our study, we chose lead-free perovskites as a more environmentally friendly option.” Although perovskites are brittle by nature, integrating them in-to PVDF-HPF gives perovskites exceptional mechanical durability & flexibility. PVDF-HPF also acts as an additional protective layer to perovskites, increasing their mechanical properties & stability.”
The result is a prototype fabric that generates 2.34 watts per square meter of electricity, enough to power small electronic devices like LEDs & commercial capacitors. Proof of Concept To demonstrate how their fabric prototype might work, the NTU scientists demonstrated how a hand tapping on a 3 x 4 cm piece of fabric can light up 100 LEDs or charge multiple capacitors, These are devices that store electrical energy and are found in devices such as mobile phones. The fabric showed good durability& stability: its electrical properties did not deteriorate after washing, folding & creasing.
It also continued to generate continuous stable electric output for up to 5 months. The scientists showed that their fabric can harness the energy from a range of human movements by attaching it to the arm, leg, hand & elbow, and to the insoles 3 of shoes, did so without impacting on movement. Professor Lee said: “Despite improved battery capacity & reduced power requirements, power sources for wearable devices still require frequent battery changes. Our results show that our prototype energy-harvesting fabric prototype can harness a human’s vibrational energy to potentially extend the life of a battery or even build self-powered systems. To our knowledge, this is the first perovskite hybrid based energy device that is stable, stretchy, breathable, waterproof, and at the same time capable of delivering outsanding electrical-output-performance.”
This fabric-based energy harvesting prototype builds-on NTU team body of work that looks at how energy generated in the environment could be scavenged. For example, the team recently developed a type of film that could potentially be mounted on roofs or walls to harness the energy created by wind or raindrops falling on-to film.