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Monday, 10 February 2020

New droplet-based electricity generator Produces 1000 times more electricity than convectional systems



Researchers have designed a system that generates electricity from falling water drops. A drop is enough to light up 100 small LEDs. This is made possible by a combination of Teflon, the semiconductor indium tin oxide and an aluminum electrode. If a drop hits this ensemble, electrical current is generated. This opens up completely new ways of generating electricity, the researchers report in the journal "Nature".



Electrical energy can be obtained from water - as evidenced by hydroelectric power plants at dams , run-of-river power plants or tidal power plants. Water can also be used to store energy. However, all of these systems require larger amounts of water to work efficiently. This is different with test systems that are based on the triboelectric effect : In these, the contact of certain materials with water causes an electrostatic charge and thus generates electricity - albeit in very small quantities.



Teflon, a semiconductor and a few pieces of aluminum

But there is another way: Researchers led by Zuankai Wang from City University Hong Kong have now developed a generator that generates electricity from individual drops of water - and this is a thousand times more efficient than previous approaches of this kind Drop generator on the interaction of water drops with certain materials.

Structure of the drop generator in the diagram and in the photo.

The device consists of a layer of indium tin oxide (ITO), on which the polymer polytetrafluoroethylene (PTFE) is applied - better known as Teflon. This electrically insulating material is a so-called electret, which can store electrical charges or accumulate, for example, through friction. A small piece of aluminum connects both layers and serves as an electrode.

Accumulating charges

If a drop of water falls on this ensemble, it spreads out on the water-repellent Teflon surface and creates an electrical charge through electrochemical interactions. In contrast to previous drop generators, this electrical energy is not lost after every drop, but accumulates. "With an increasing number of water drops hitting the surface, the charge increases," report Wang and his team. "After around 16,000 drops, the surface charge reaches a stable value of around 50 nanocoulombs."

Now a second process comes into play: The water spreading on the surface forms a bridge between the aluminum electrode and the ITO and Teflon layer. This creates an electrical circuit through which the charge can flow. As the researchers explain, the functioning of the system is similar to that of a field effect transistor. According to her, the drop generator achieves an energy density of 50 watts per square meter.

One drop lights up 100 LEDs

In initial tests, a prototype of this drop generator already generated a thousand times more energy than conventional systems: "A drop of 100 microliters of tap water that falls from a height of 15 centimeters can generate a voltage of 140 volts and a current of 270 microamperes," report Wang and his team. "This electrical energy is sufficient to make a hundred small LEDs light up."

According to the researchers, their drop generator can be used not only with tap water, but also for sea water and raindrops. They adapted the design for use in the rain so that the rainwater is first collected and then divided into small, regularly falling droplets by a capillary. Seawater can be dosed in a similar way.

"By adjusting the diameter of the capillary and the drop height, we can control the size and speed of the drops and thus the amount of energy generated," explains Wang and his colleagues.



Renewable, decentralized energy

According to the scientists, this technology opens up new possibilities for using the energy of water. "The kinetic energy of the falling water comes from gravity and can therefore be viewed as freely available and renewable," says Wang. “It should therefore be used better. Electricity from drops of water instead of oil or nuclear power could advance the sustainable development of the world."

The drop generator is particularly suitable for decentralized power generation. Wherever rain falls or there is water, it could be used to generate electrical energy - even on the hull of a ferry or on the surface of an umbrella.


Bibliography:

Xu, W., Zheng, H., Liu, Y. et al.

A droplet-based electricity generator with high instantaneous power density.

Nature (2020).

https://doi.org/10.1038/s41586-020-1985-6

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