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

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

Friday, 24 January 2020

New UV-C laser diode promises to disinfect your various health conditions

Structure and prototype of the UV-C laser diode. [Image: Asahi Kasei Corp / Nagoya University]


Japanese researchers made a laser diode that emits the shortest wavelength ultraviolet light ever achieved, covering an area of ​​applications that until now has not benefited from lasers.

These new devices could be used for health disinfection, treatment of skin diseases, such as psoriasis, and gas and DNA analysis.

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"Our laser diode emits the shortest wavelength in the world, at 271.8 nanometers (nm), under injection of alternating [electrical] current at room temperature," announced Professor Chiaki Sasaoka, from Nagoya University.

Previous efforts in the development of ultraviolet laser diodes have only managed to achieve emissions up to 336 nm, explains Sasaoka, not reaching the short-wavelength ultraviolet, or UV-C, which is in the range between 200 and 280 nm.


Material quality

To overcome the various problems that had been preventing the manufacture of this UV-C diode, the team used a high quality aluminum nitride (AlN) substrate as a basis to form the layers of the laser diode. The quality of the material was essential, since the lower quality AlN contains a large number of defects, which end up affecting the efficiency of the active layer of the laser diode in converting electrical energy into light energy.

In a laser diode the ‘p-type’ and ‘n-type’ layers are separated by a ‘quantum well’. When an electric current is passed through a laser diode, positively charged openings in the p-type layer and negatively charged electrons in the n-type flow flow to the center to connect, energy in the form of light particles called photons, is released.

The researchers designed quantum so well that it emitted deep UV light. P and N type layers consist of aluminum gallium nitride (AlGaN). The cladding layer, also made of AlGaN, is arranged on both sides of the p and n layers. The layer below the n-type layer contains silicon impurities, a process called doping. Doping is used as a technique to change material properties.

The layer above the p-type layer is subject to distributed polarization doping which touches the layer without adding impurity.

The aluminum content of the p-side layer is designed so that it is highest at the bottom and reduced at the top. The researchers believe that this aluminum gradient increases the flow of positively charged openings. Finally, a top contact layer was added, which consisted of p-type AlGaN magnesium alloy.



The researchers found that the doping of polarization - insertion of elements to change the behavior of the material - of the coating layer on the positive side ensured operation with a "remarkably low operating voltage" of 13.8V, and the emission "of the shortest length of wave reported so far ".

Asahi Kasei Corporation has already taken an interest in the project, and will help researchers develop deep UV lasers to come up with a commercial product.


Bibliography:

Article: A 271.8 nm deep-ultraviolet laser diode for room temperature operation

Authors: Ziyi Zhang, Maki Kushimoto, Tadayoshi Sakai, Naoharu Sugiyama, Leo J. Schowalter, Chiaki Sasaoka, Hiroshi Amano

Magazine: Applied Physics Express

DOI: 10.7567 / 1882 -0786 / ab50e0

Saturday, 14 December 2019

Scientists discovered cheaper way to make hydrogen from water


Researchers have discovered a cheaper way to make hydrogen from water: a team of scientists led by the UNSW has demonstrated a sustainable way to get hydrogen, which is necessary, among other things, for fueling vehicles hydrogen.

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Scientists from UNSW Sydney, Griffith University and Swinburne University of Technology have demonstrated that the capture of hydrogen by separating it from oxygen in water can be done using low-metals cost like iron and nickel (as catalysts), which speeds up the chemical reaction, while requiring less energy.

It should be noted that iron and nickel, which are found in abundance on Earth, would replace ruthenium, platinum and iridium, precious metals which until now have been considered as reference catalysts in the process of "Water fractionation".



Professor Chuan Zhao, of the UNSW School of Chemistry, explains that in water fractionation, two electrodes apply an electrical charge to the water, which allows the hydrogen to be separated from the water. 'oxygen. It can then be used as an energy carrier in a fuel cell.

“ What we do is coat the electrodes with our catalyst to reduce energy consumption. On this catalyst, there is a tiny nanoscale interface where iron and nickel meet at the atomic level, which then becomes an active site for water separation: this is where hydrogen can be separated from oxygen and captured as fuel, and oxygen can be released as environmentally friendly waste,” he explains.

Iron and nickel, but on a nanometric scale

Already in 2015, Professor Zhao's team invented a nickel-iron electrode for generating oxygen with unprecedented efficiency. However, Zhao believes that iron and nickel alone are not good enough catalysts for the generation of hydrogen, but that it is when they meet on the nanometric scale that the “magic operates ".

Nanoparticle design and electron microscopies. a Schematic representation of the Ni and Fe nanoparticles and the Ni-Fe Janus nanoparticles synthesis through the oleate-assisted micelle formation and the illustration on the HER across the Ni-γ-Fe2O3 interface in alkaline medium. b STEM-HAADF image of a single Ni–Fe NP nanoparticle and its corresponding EDS line-scan spectrum (scale bar: 1 nm). c High-resolution EDS mapping on STEM-HAADF images of the nanoparticles for Ni and Fe, selected area electron diffraction inset (image scale bars: 20 nm; SAED scale bar: 2 nm−1).


The nanoscale interface fundamentally changes the properties of these materials. Our results show that the nickel-iron catalyst can be as active as platinum in the generation of hydrogen,  ”he explains. "  An added benefit is that our nickel-iron electrode can catalyze both hydrogen and oxygen generation, so not only could we reduce production costs by using elements that are abundant on Earth, but also allow the use of one catalyst instead of two . ”

And indeed: a quick glance at current metal prices clearly demonstrates why this could be the change needed to accelerate the transition to the so-called hydrogen economy. Iron and nickel are priced at € 0.12 and € 19.65 per kilogram respectively. On the other hand, ruthenium, platinum and iridium are priced at € 10.6, € 37.9 and € 62.6 per gram respectively. In other words, thousands of times more expensive.



“ Right now, in our fossil fuel economy, we have this great incentive to move to a hydrogen economy so that we can use hydrogen as a clean and abundant energy carrier on Earth. Many people have been talking about the hydrogen economy for ages, but this time it seems like it really does happen  , "said Professor Zhao.

According to him, if water separation technology is developed, there could one day be hydrogen refueling stations (just like the service stations we know today), where we could refuel our hydrogen vehicles with hydrogen produced by this water division reaction. This could be done in a few minutes, compared to recharging hours in the case of electric cars with lithium battery.


Bibliography:

Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide
Bryan H. R. Suryanto, Yun Wang, Rosalie K. Hocking, William Adamson & Chuan Zhao

Nature Communications volume 10, Article number: 5599

http://dx.doi.org/10.1038/s41467-019-13415-8

Thursday, 12 December 2019

New study: Energy can be stored in the mountains using sand

Energy can be stored as sand or water for as long as needed.

Store energy in the mountains

Storing energy for long periods of time is one of the biggest challenges for a permanent move to a renewable and environmentally friendly energy matrix.

Solar energy, wind energy, wave energy, tidal energy and others are widely available, but they cannot maintain a constant supply of energy needed to meet the continuing demand of society.

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Julian Hunt and colleagues from Austria, Denmark and Italy believe they have come up with a suitable solution for situations where current alternatives do not apply - such as underwater hydropower , flow batteries and various ways of " storing the wind ", for example. .

The concept was named MGES for "mountain gravity energy storage" - and can be combined with a hydroelectric dam.


Generate electricity with sand

MGES consists of placing cranes on the edge of a steep mountain with sufficient reach to carry sand (or gravel) from a base storage to a mountain top storage location. An engine / generator moves sand-filled storage containers from the bottom up, similar to a cable car.

During this process, the potential energy is stored. Electricity is generated by lowering the sand from the upper storage location back to the base, harnessing the energy of the descending containers like a zip line.

If there are streams in the mountain, the MGES system can be hybridized with hydropower, where water would be used to fill storage containers in periods of high availability rather than sand or gravel, generating power.

MGES systems have the benefit that water can be added at any time in the system, thus increasing the possibility of capturing water from different heights on the mountain, which is not possible with conventional hydroelectric dams.

The nuclear fusion continues in a very distant future, so there are those who still bet on cold fusion

Sand does not evaporate

"One of the benefits [of the MGES system] is that sand is cheap and, unlike water, doesn't evaporate - so you never lose potential energy, and it can be reused countless times. That makes it particularly interesting for dry regions.

"In addition, hydroelectric plants are limited to a height difference of 1,200 meters due to very high hydraulic pressures. MGES plants can have height differences of more than 5,000 meters.

"Regions with high mountains, for example the Himalayas, Alps and Rockies, could therefore become important long-term energy storage centers. Other interesting places for MGES are islands such as Hawaii, Cape Verde, Madeira and the Isles. Pacific, with steep mountain terrain, "detailed Hunt.

To test the concept, the team proposed a future energy matrix for Molokai Island in Hawaii, using only wind , solar , batteries and MGES to meet the island's energy demand.

Although designed to store electricity on a large scale, liquid batteries are being tested in electric cars

Store energy

Hunt emphasizes that MGES technology is not suitable for meeting peak demand or storing energy in daily cycles; Its main advantage is to fill a gap in the market as a long term energy storage location.

MGES systems could, for example, store energy continuously for months and then generate electricity continuously for months or when water is available for hydropower, while batteries would handle daily storage cycles.



"It's important to note that MGES technology does not replace current energy storage options, but opens up new ways to store energy and harness untapped water potential in high mountain regions," said Hunt.




Bibliography:

Article: Mountain Gravity Energy Storage: A new solution for closing the gap between existing short- and long-term storage technologies

Authors: Julian David Hunt, Behnam Zakeri, Giacomo Falchett, Andreas Nascimento, Yoshihide Wada, Keywan Riahi

Journal: Nature Energy

DOI: 10.1016 / j.energy.2019.116419

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