Approaches for harnessing ocean energy have been explored as a solution to the pollution caused by thermal power generation. Nanogenerators, including piezoelectric, triboelectric and pyroelectric, are key technologies used for mechanical energy conversion.
A triboelectric nanogenerator (TENG) makes use of the triboelectric effect and electrostatic induction to harvest mechanical energy based on contact or sliding electrification.
Conventional TENG devices are often based on solid/solid contact, and it is hard to ensure contact intimacy of the two tribo-materials. Material surfaces can wear or become damaged after long-term friction, and the solid-contact-based TENGs need shell structures and mechanical components such as springs, holders and rotors to harvest vibration energy.
According to the CUHK team, these limitations have been overcome with the development of its water-tube-based TENG (WT-TENG) for irregular and low-frequency environmental energy harvesting.
Researchers said they encapsulated water in a finger-sized tube. When water moves in the tube between regions of the two electrodes, triboelectrification happens and electric currents can be generated. The WT-TENG can operate in various modes, the team said, including rotation, swing, see-saw and horizontal linear modes to harvest energy from diverse mechanical movements such as ocean wave, wind, body and vehicle movements.
The output volumetric charge density of the WT-TENG reportedly reached 9mC/m3 at a frequency as low as 0.25Hz. Multiple small WT-TENG units can also be combined into one larger unit, researchers confirmed.
Led by Zi Yunlong, associate professor in CUHK’s Department of Mechanical and Automation Engineering, the team designed two power generation units: a box with 34 WT-TENG units placed in the sea to collect wave energy, and a wristband composed of 10 WT-TENG units. When tested, the peak power generations of the two were confirmed to be sufficient for driving 150 LED light bulbs.
“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,” said Yunlong. “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.