Water-filled nanogenerators harvest energy from just about any movement
There are energy sources all over the place, if you know where to look. Researchers at the Chinese University of Hong Kong (CUHK) have now designed new modular nanogenerators that can harvest energy from a variety of different types of motion, such as ocean waves or a person's body movements.
The new devices are a type of triboelectric nanogenerator (TENG), which generate electricity through friction. These systems have shown promise in harvesting energy from body movements, touchscreen taps, footsteps on flooring, and even raindrops rolling down solar cells.
But as the CUHK team says, one of the main limitations for TENGs is that they require solid surfaces to remain in contact for long periods, which can be hard to sustain. Plus, over time they can damage each other.
For the new device, the researchers tapped into the friction between a solid and a liquid. They filled a finger-sized plastic tube with deionized water, which can produce electricity as this water sloshes around between two electrodes. The team calls the resulting device a water-tube-based triboelectric nanogenerator (WT-TENG).
Because the water can maintain contact with the electrodes more easily, the team says that the WT-TENGs have higher output volumetric charge densities. They report that it reaches 9 milliColoumbs per m3, at frequencies down to just 0.25 Hz. That’s not a whole lot on their own, but the units are modular so they can be combined into larger generators.
This design has several advantages, the team says. Not only do they not need any other moving parts, like springs or rotors, but they can harvest energy from a range of different motions. The team tested their generating abilities in rotation, swinging, seesawing and side-to-side motions, and found they worked well in all movements. This suggests they could be useful to harvest energy from a variety of sources, like devices that attach to vehicles, float on ocean waves, or wearables that harness a user’s body movements.
In experiments, the team tested the latter two of these setups. In one, 34 WT-TENG units were combined into one box and floated on the sea to harvest wave energy, while in the second, the team made a wristband out of 10 WT-TENGs. Both setups generated enough electricity to power 150 LEDs.
“Previous designs of ocean energy harvesters have been equipped with electromagnetic-based generators which are large in size and heavy, and will only generate power if the frequency of ocean waves reaches a certain high level,” says Zi Yunlong, corresponding author of the study. “Our latest research has overcome the technical hurdles and will promote the use of nanogenerators, especially in “blue energy” harvesting, offering a new direction for the development of renewable energy to achieve carbon neutrality.”
The research was published in the journal Advanced Energy Materials, and the team demonstrates the range of motions in the video below.