The solution to saving energy might not be something big—it could be small. Nanoscale, to be exact.
There’s a lot of energy in the world that goes uncollected. Engines rattle around in their casings, breezes blow too weakly to turn a windmill, and clothes rustle as we walk. But hypothetically, all this energy could be harvested and recycled with devices called nanogenerators. They turn friction into electricity. The concept has been around for a while, but so far it’s been hard to make a device that’s cost-efficient enough to mass-produce and collect energy on a large scale.
An engineering team has moved closer to putting the idea into practice. In a new study in Advanced Functional Materials, they report the lightest generator ever made, weighing less than a tenth of a gram. It’s able to harness even small amounts of friction—tapping it repeatedly with a finger allows it to power a grid of 20 LED lightbulbs.
“This is the lightest nanogenerator ever reported so far,” said Wenzhuo Wu, an engineering professor at Purdue University who wasn’t involved in the study. “I am very impressed by the elegant design.”
Nanogenerators of this general type have just a few basic components. In the center, two surfaces that can conduct energy lie against each other. When there’s pressure on the device, the two surfaces rub together and build up static energy from the friction—just like when your fleece jacket rubs against your sweater underneath. Electrodes then carry the charge away to a circuit or a rechargeable battery. Two durable outer layers hold all those parts in the right place and shape, protecting the more fragile inner parts.
The engineers made their nanogenerator even simpler and lighter by using one part for two purposes. Carbon substances are both strong and able to conduct energy. The team used a spongy layer of carbon to hold the charging surfaces in place and to carry the electricity generated within the device.
Because of their tiny size, nanogenerators like this one could be used to power portable electronics like smartphones and activity trackers, said Xia Cao, an author of the new study and an engineering professor at the University of Science and Technology Beijing.
While this device was a prototype, the engineers showed that their design is efficient enough for mass production, said San-Woo Kim, a materials science professor at Sungkyunkwan University in South Korea. The simplified design opens the way for similar devices.
“Compared to other energy harvesting technologies… [this] generator is a very promising technology, because it can generate a very high electrical output with a wide range of materials choices,” Kim said.
Since this type of nanogenerator is both durable and cheap, Wu said that it could challenge other alternative energy sources like solar panels, which still have high material costs, despite recent advances . “This can be very competitive,” he said.