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Showing posts with label Energy. Show all posts
Showing posts with label Energy. Show all posts

Wednesday, 19 February 2020

New device generates electricity from moisture in the air


In the race for renewable energies, engineers are redoubling their inventiveness to find and exploit the energies freely available from the environment. But sometimes it's nature itself that gives scientists a boost. This is particularly the case of a very specific bacterium, Geobacter sulfurreducens, whose bacterial nanowires naturally conduct electricity. And researchers used these nanowires to create a device that generates electricity from the humidity of the air.

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This unusual bacterium, belonging to the genus Geobacter, was first spotted for its ability to produce magnetite in the absence of oxygen, but over time scientists discovered that it could also make other things, like bacterial nanowires that conduct electricity.

For years, researchers have tried to find ways to use this natural gift usefully. And they recently did it with a device called Air-gen.

According to the team, their device can generate electricity from practically nothing. “We literally generate electricity from the air. Air-gen generates clean energy 24/7,” said Jun Yao, electrical engineer at the University of Massachusetts. The study was published in the journal Nature.



Generate electricity via air humidity thanks to nanowires from G. sulfurreducens

The claim may seem exaggerated, but a new study by Yao and his team describes how the generator can indeed create electricity with nothing but the presence of air around it. All this thanks to the nanowires of electrically conductive proteins produced by Geobacter ( G. sulfurreducens, in this case).

The Air-gen consists of a thin film of protein nanowires measuring only 7 micrometers thick, positioned between two electrodes, but also exposed to air.

(A) Bacterial nanowires and generator structure. (B, C, D) Properties of the output voltage. Credits: Xiaomeng Liu et al. 2020


Due to this exposure, the nanowire film is capable of absorbing water vapor present in the atmosphere, allowing the device to generate a direct electric current conducted between the two electrodes. The team says the charge is likely created by a humidity gradient that causes protons to diffuse into the nanowire material.

"This diffusion of charges should induce an electric field of counterweight or a potential similar to that of membranes at rest in biological systems. A maintained humidity gradient, which is fundamentally different from anything seen in previous systems, explains the continuous output voltage of our nanowire device.”

Hydroelectric production more efficient than graphene

The discovery was made almost by accident, when Yao noticed that the devices he was experimenting with were conducting electricity apparently on their own. “I saw that when the nanowires were in contact with electrodes in a specific way, the devices generated a current. I found that exposure to atmospheric humidity was essential and that protein nanowires absorb water, producing a voltage gradient across the device.”

Properties of the voltage supplied by the generator. The generation of 0.5 V continuously allows powering small electronic devices. Credits: Xiaomeng Liu et al. 2020

Previous research has demonstrated the production of hydroelectric power using other types of nanomaterials - such as graphene, but these attempts have largely produced only short bursts of electricity, lasting only a few seconds. In contrast, the Air-gen produces a sustained voltage of approximately 0.5 V, with a current density of approximately 17 microamps per square centimeter.

Towards large-scale energy production

It doesn't take a lot of energy, but the team says connecting multiple devices could generate enough to charge small devices like smartphones and other personal electronics - all without wasting and using only ambient humidity (even in regions as dry as the Sahara Desert).

“The ultimate goal is to build systems on a large scale. Once we reach an industrial scale for the production of nanowires, I expect we will be able to build large generation systems that will make a major contribution to sustainable energy production," said Yao, explaining that the efforts future could use the technology to power homes via nanowires embedded in the mural.



If there is one obstacle to realizing this seemingly incredible potential, it is the limited amount of nanowires produced by G. sulfurreducens. Related research from one of the teams - microbiologist Derek Lovley, who first identified Geobacter bacteria in the 1980s - may have a solution: genetically designing other bacteria, such as E. coli, to perform the same process in larger proportions.


Bibliography:

Power generation from ambient humidity using protein nanowires.

Xiaomeng Liu, Hongyan Gao, Joy E. Ward, Xiaorong Liu, Bing Yin, Tianda Fu, Jianhan Chen, Derek R. Lovley, Jun Yao.

Nature, 2020;

DOI: 10.1038/s41586-020-2010-9

Friday, 14 February 2020

Movement of a liquid droplet on MoS2 generates over 5 volts of electricity


Japanese scientists have developed an energy capture device that generates more than 5 volts of electricity from a single drop of liquid rolling downhill. It was already known that a sheet of graphene can generate electricity from the movement of a liquid on its surface. However, the output voltage is limited to about 0.1 volts, which is not enough to drive electronic devices.

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The result was much better using molybdenite , or molybdenum disulfide (MoS2), as the active material in the nanogenerator, allowing to reach just over 5 volts of electricity from a drop of liquid rolling over the surface of the thin and flexible material - molybdenite is one of the stars of ultrafine electronics , surpassing graphene in several ways.

This voltage is important because it is at the level required for any electronic circuit, but the current generated by a single drop is also miniscule, with peaks of six nanowatts, which directs the nanogenerator for applications where there are continuous flows of liquids.



"To use MoS2 for the generator, it was necessary to form a large-area single-layer MoS2 film on a plastic film. With conventional methods, however, it was difficult to grow MoS2 uniformly on a large-area substrate," says Professor Ohno of the Institute of Materials and Systems for Sustainability at Nagoya University. "In our study, we succeeded in fabricating this form of MoS2 film by means of chemical vapor deposition using a sapphire substrate with molybdenum oxide (MoO3) and sulphur powders. We also used a polystyrene film as a bearing material for the MoS2 film, so that we were able to transfer the synthesized MoS2 film to the surface of the plastic film quite easily."

Harvesting Energy

The harvest of energy , incorporated in nanogenerators capable of transforming small amounts of naturally occurring energy (by light, heat and vibration) into electricity, is gaining attention as a method to power the Internet of Things (IoT) devices.

This technology is expected to have applications, for example, in autonomous and self-powered sensors, which will be able to work continuously without any concern with power or battery change.

The newly developed generator is flexible enough to be installed on the curved inner surface of plumbing, and is thus expected to be used to power IoT devices used in liquids, such as self-powered rain gauges and acid rain monitors, as well as water quality sensors that can generate power from industrial wastewater while monitoring it.



Professor Ohno says, "Our MoS2 nanogenerator is able to harvest energy from multiple forms of liquid motion, including droplets, spraying, and sea waves. From a broader perspective, this device could also be used in applications involving hydrodynamics, such as generating electricity from rainwater and waterfalls."


Bibliography:

Article: High output voltage generation of over 5 V from liquid motion on single-layer MoS2

Authors: Adha Sukma Aji, Ryohei Nishi, Hiroki Ago, Yutaka Ohno

Magazine: Nano Energy

Vol .: 68, 104370

DOI: 10.1016 / j. nanoen.2019.104370

Tuesday, 11 February 2020

New Electricity generator powers 100 small LED bulbs with a single drop of water

City University HK


Liquid water is omnipresent on Earth, from rivers to oceans through rain. However, the energy potential it contains is still insufficiently exploited. Recently, a team of Chinese engineers has developed a new method capable of harnessing the kinetic energy of water movements, such as falling raindrops, and converting it into electricity. A single drop of rain could thus power 100 LED bulbs.

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A single drop of rain can now power 100 small LED bulbs, setting a new milestone for energy generation technologies. The droplet-based electricity generator developed has a high energy conversion efficiency and a power density a thousand times greater than its counterparts. The study was published in the journal Nature .

The developers hope the technology will help tackle the global energy crisis by providing new ways to use the environmental energy that surrounds us in water and rain. The generator could be used in a variety of contexts where water meets a solid surface - such as on boat hulls, along coasts and even above shelters or umbrellas.

“Our research shows that a drop of 100 microliters of water released from a height of 15 centimeters can generate a voltage of more than 140 volts. The power generated can light up 100 small LED bulbs,” said Zuankai Wang, engineer at City University of Hong Kong.



Limited current hydroelectric technologies

Although the concept of hydroelectricity is not new - hydroelectric dams and tidal power plants operate around the world, the limitations of current technology have prevented us from taking full advantage of the available energy from waves and raindrops. This power is in the form of low frequency kinetic energy. “The kinetic energy caused by waterfalls is due to gravity and can be considered free and renewable. It should be used better.”

Conventional droplet energy generators take advantage of the triboelectric effect, in which electricity is generated when certain materials come into contact with each other, friction causing them to exchange electrons . Unfortunately, the size of the charge that can be generated on such surfaces is generally very limited, leading to very low energy conversion efficiency. The researchers' new energy recovery method overcomes these limitations in two different ways.

Optimized electricity generation thanks to polytetrafluoroethylene

First, the team used a material called polytetrafluoroethylene (or PTFE), which has an almost permanent electrical charge. They found that when drops hit the PTFE, the charges on its surface gradually accumulated until reaching a saturation point - which allowed them to overcome the bottleneck presented by the previous approaches, which could not accumulate only small charges.

(Left): the technology uses the kinetic energy generated by the drop of the drops on the electrodes in order to generate electricity. (Right): diagram of the structure of the PTFE-based device. Credits: City University HK


The second characteristic of the new method is its resemblance to a field effect transistor - a basic element of modern electronics and for which the 1956 Nobel Prize in physics was awarded. The design of the power generator includes two electrodes - one made of aluminum, the other made of tin and indium oxide with a PTFE coating, on which the charge is generated.

Many potential applications

When droplets fall on this last surface, they connect the two electrodes, transforming the original configuration into an electric circuit in a closed loop, releasing the stored charge and generating an electric current to power the LEDs. The researchers also found that the technique is not affected by lower relative humidities - and that it works with both rainwater and seawater.



According to the researchers, the concept could be used on various surfaces where liquids come into contact with solids, to fully exploit the low frequency kinetic energy that can be found in water. Professor Wang said he hopes the technology will help harvest energy from water to tackle the global problem of renewable energy shortages. Researchers have patented their technology in the United States and mainland China.


Bibliography:

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

Authors: Wanghuai Xu, Huanxi Zheng, Yuan Liu, Xiaofeng Zhou, Chao Zhang, Yuxin Song, Xu Deng, Michael Leung, Zhengbao Yang, Ronald X. Xu, Zhong Lin Wang, Xiao Cheng Zeng & Zuankai Wang

Nature (2020).

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

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".

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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

Tuesday, 4 February 2020

Anti-solar cell: a photovoltaic cell that works at night



One of the major drawbacks of photovoltaic solar panels is that they do not produce electricity at night. The energy generated during the day must therefore be stored for use in the evening. What if we could develop solar panels that generate electricity at night? Jeremy Munday, professor in the Department of Electrical and Computer Engineering at UC Davis, says it is entirely possible. A specially designed photovoltaic cell could generate up to 50 watts of energy per square meter under ideal conditions at night, about a quarter of what a conventional solar panel can generate during the day.

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Munday, who recently joined UC Davis, is developing prototypes of these nocturnal solar cells capable of generating small amounts of energy. The researchers now hope to improve the power output and the efficiency of the system.

The operation would be similar to that of a normal solar cell, but involves a reverse process. An object that is warm relative to its surroundings will emit heat in the form of infrared light. A conventional solar cell is cold (compared to solar radiation), so it absorbs light.



Space is an extremely cold place, so if a hot object is pointed at the sky, it will radiate heat towards it. This phenomenon has been used in particular for night cooling for hundreds of years. "Over the past five years, there has been a lot of interest in devices that can generate energy during the day (by harnessing sunlight)," said Munday.

A conventional photovoltaic cell (left) absorbs photons from sunlight and generates an electric current. A thermoradiative cell (on the right) generates an electric current when it radiates infrared light (heat) towards the extreme cold of deep space. UC Davis engineers suggest that such cells could generate a significant amount of energy and help balance the power grid over the day-night cycle. Credits: Tristan Deppe / Jeremy Munday, UC Davis


Generate energy by radiating heat

There is another type of device called a “thermoradiative cell”, which generates energy by radiating heat to its environment. Researchers have notably explored its use to capture residual heat from engines.

"We said to ourselves, what if we took one of these cells and placed it in a hot area with the sky pointing at it," said Munday. This thermoradiative cell pointed towards the night sky would emit infrared radiation because it is hotter than outer space.

“An ordinary solar cell generates energy by absorbing sunlight, which causes voltage to appear across the device and the flow of current. In these new devices, the light is rather emitted and the current and voltage go in the opposite direction, but it still generates energy," said Munday. "It requires different materials, but the physics is the same."



The device would also work during the day, as long as direct sunlight is blocked. Because this new type of solar cell could potentially operate 24 hours a day, it is an attractive option for balancing the electrical network on the day-night cycle.


Bibliography:

Nighttime Photovoltaic Cells: Electrical Power Generation by Optically Coupling with Deep Space

Tristan Deppe Jeremy N. Munday*

ACS Photonics 2020, 7, 1, 1-9

Publication Date:November 20, 2019

https://doi.org/10.1021/acsphotonics.9b00679

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