A newly developed water-tube-based triboelectric nanogenerator effectively transforms several irregular and low frequency mechanical energies, such as ocean wave energy, into electricity, opening a new path for developing 'blue energy.'
The triboelectric nanogenerator was recently developed by a group of researchers from the Chinese University of Hong Kong (CUHK), Faculty of Engineering.
Nearly 70% of the Earth’s surface area is covered by oceans, which are the largest reservoirs of energy. Scientists have been investigating the method for tapping ocean energy to find a solution to the global energy crisis and pollution problems due to thermal power generation.
The nanogenerator integrates triboelectric, piezoelectric and pyroelectric nanogenerators and is one of the main technologies for mechanical energy conversion. The triboelectric nanogenerator (TENG) uses the triboelectric effect and electrostatic induction to harness mechanical energy depending on contact or sliding electrification.
But traditional TENG device usually depends on solid-to-solid contact, and it is difficult to guarantee the close contact of the two tribo-materials. At the same time, the surfaces of the materials will wear out or get damaged upon exposure to long-term friction.
The solid-to-solid-based TENGs require shell structures and/or mechanical components like rotors, holders and springs to harness random vibration energy. The complicated structure will decrease the efficiency of harnessing energy.
Under the guidance of Professor Zi Yunlong, Assistant Professor of the Department of Mechanical and Automation Engineering at CUHK, the researchers have recently solved the above technical restrictions and designed a water-tube-based TENG (WT-TENG) for irregular and low frequency environmental energy harvesting, like water waves.
The researchers enclosed water in a finger-sized tube (FEP). The movement of water in the tube between regions of the two electrodes leads to the formation of triboelectrification, thus enabling the production of electric current.
By leveraging water’s flexibility, the WT-TENG can be made to function in several modes, such as seesaw, swing, rotation and horizontal linear modes, to harness energy from various mechanical movements in the surrounding, like wind, ocean waves, vehicle, and body movements.
As a result of the high contact closeness present between the water and the tube surface, the output volumetric charge density of the WT-TENG is considerably improved, thereby achieving 9 mC/m3 at a frequency as low as 0.25 Hz, which is more than all earlier reports.
Furthermore, quite similar to toy building bricks, several small WT-TENG units can be simply integrated and combined as one bigger unit to achieve multiplied electric outputs. Scientists developed two power generation units.
The first one is a box with 34 WT-TENG units, which was positioned in the sea to gather ocean wave energy.
The second one is a wristband made of 10 WT-TENG units. One of the researchers worn it on and continued to swing her arms for body motion energy harnessing. The maximum power generations of the two tests were both sufficient to power 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. 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 carbo neutrality.
Zi Yunlong, Assistant Professor, Department of Mechanical and Automation Engineering, Chinese University of Hong Kong
The article’s first author is Postdoctoral Fellow Dr Wu Hao, and Professor Zi Yunlong is the only corresponding author. Professor Wang Zuankai from the City University of Hong Kong contributed to the study by offering guidance.
Wu, H., et al. (2021) Multi‐Mode Water‐Tube‐Based Triboelectric Nanogenerator Designed for Low‐Frequency Energy Harvesting with Ultrahigh Volumetric Charge Density. Advanced Energy Materials. doi.org/10.1002/aenm.202100038.