Researchers at Swinburne University of Technology’s Centre for Translational Atomaterials have developed a highly efficient solar absorbing film that absorbs sunlight with minimal heat loss and rapidly heats up to 83°C in an open environment.
The graphene metamaterial film has great potential for use in solar thermal energy harvesting and conversion, thermophotovoltaics (directly converting heat to electricity), solar seawater desalination, wastewater treatment, light emitters and photodetectors.
The researchers have developed a prototype to demonstrate the photo-thermal performance and thermal stability of the film. They have also proposed a scalable and low-cost manufacturing strategy to produce this graphene metamaterial film for practical applications.
“In our previous work, we demonstrated a 90 nm graphene metamaterial heat-absorbing film,” says Professor Baohua Jia, founding Director of the Centre for Translational Atomaterials.
“In this new work, we reduced the film thickness to 30 nm and improved the performance by minimising heat loss. This work forms an exciting pillar in our atomaterial research.”
Lead author Dr. Keng-Te Lin says: “Our cost-effective and scalable structured graphene metamaterial selective absorber is promising for energy harvesting and conversion applications. Using our film an impressive solar to vapour efficiency of 96.2 percent can be achieved, which is very competitive for clean water generation using renewable energy source.”
Co-author Dr. Han Lin adds: “In addition to the long lifetime of the proposed graphene metamaterial, the solar-thermal performance is very stable under working conditions, making it attractive for industrial use. The 30 nm thickness significantly reduced the amount of the graphene materials, thus saving the costs, making it accessible for real-life applications.”
More information: Keng-Te Lin et al. Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion, Nature Communications (2020). DOI: 10.1038/s41467-020-15116-z
Electrons can behave like a viscous liquid as they travel through a conducting material, producing a spatial pattern that resembles water flowing through a pipe. So say researchers in Israel and the UK who have succeeded in imaging this hydrodynamic flow pattern for the first time using a novel scanning probe technique. The result will aid developers of future electronic devices, especially those based on 2D materials like graphene in which electron hydrodynamics is important.
We are all familiar with the distinctive patterns formed by water flowing in a river or stream. When the water encounters an obstacle – such as the river bank or a boat – the patterns change. The same should hold true for electron flow in a solid if the interactions between electrons are strong. This rarely occurs under normal conditions, however, since electrons tend to collide with defects and impurities in the material they travel through, rather than with each other.
Making electrons hydrodynamic
Conversely, if a material is made very clean and cooled to low temperatures, it follows that electrons should travel across it unperturbed until they collide with its edges and walls. The resulting ballistic transport allows electrons to flow with a uniform current distribution because they move at the same rate near the walls as at the centre of the material.
If the temperature of this material is then increased, the electrons can begin to interact. In principle, they will then scatter off each other more frequently than they collide with the walls. In this highly interacting, hydrodynamic regime, the electrons should flow faster near the centre of a channel and slower near its walls – the same way that water behaves when it flows through a pipe.
Extremely clean 2D materials
In recent years, researchers have created extremely clean samples from 2D materials such as graphene to act as testbeds for studying electron hydrodynamics. The vast majority of this work, however, involved measuring electron transport, which only probes the physics of electrons at fixed positions along the perimeter of the device.
“Hydrodynamics, on the other hand, brings to mind dynamic images of electrons swirling around with interesting spatial patterns,” says Joseph Sulpizio, who is one of the lead authors of this new study. “Such patterns have been predicted in theory but never imaged spatially.”
Poiseuille current profile
Sulpizio and the other researchers, led Shahal Ilani at Israel’s Weizmann Institute for Science in collaboration with Andre Geim’s group at Manchester University, have now imaged the most fundamental spatial pattern of hydrodynamic electron flow for the first time. They obtained this parabolic or Poiseuille current profile by studying electrons travelling through a conducting graphene channel sandwiched between two hexagonal boron nitride layers equipped with electrical contacts.
Under an applied electric field, the electrons produce a voltage gradient along the current flow direction. Unfortunately, this local voltage gradient is the same for both hydrodynamic and ballistic electron flow and so cannot be used to distinguish between the two regimes. Ilani and colleagues overcame this problem by applying a weak magnetic field to the sample, which produces another voltage – the Hall voltage – perpendicular to the direction of the current. The gradient of this voltage is very different for hydrodynamic and ballistic flow.
The researchers imaged the Hall voltage profile for both flow regimes using a scanning probe recently developed in their laboratory. This ultraclean carbon nanotube single-electron-transistor-based device is held at cryogenic temperatures and is extremely sensitive to local electrostatic fields. The current flowing through it is thus indicative of the local potential of the sample and voltage gradients associated with the Hall voltage.
By measuring this current, the team was also able to observe the transition between the regime in which electron-electron scattering dominates and that in which the electrons flow ballistically. “As expected, we observed a flat Hall field profile across the graphene channels at low temperatures,” Sulpizio tells Physics World. “Upon heating, however, the profile becomes strongly parabolic, revealing less current flow near the walls and more near the centre, which indicates the transition to hydrodynamic/Poiseuille flow.”
The implications of the work, which has been published in Nature, are many, he says. Electron hydrodynamics only emerges at elevated temperatures (in contrast to many other kinds of electronic phenomena that exist only at very low temperatures) and this will be relevant for technological devices like computer chips that operate at room temperature. It will also be relevant in 2D van der Waals heterostructures like those made from graphene, and especially when they are super-clean. This behaviour is likely to play an important role in new generations of devices made from these materials.
“Looking further ahead, it might even be possible one day to engineer fundamentally new kinds of electronic devices that directly exploit electron hydrodynamics,” Sulpizio says. “When electrons interact hydrodynamically, their viscosity results in highly non-local spatial flow patterns that might be technologically advantageous.”
A toothpaste-like composite with hexagonal boron nitride developed by researchers at Rice University is an effective electrolyte and separator in lithium-ion batteries intended for high-temperature applications in a number of industries, including aerospace and oil and gas. (Source: Jeff Fitlow/Rice University)
One major and dangerous problem with lithium-ion batteries is that they can catch fire when heated to high temperatures, an issue that has caused damage and even death when devices ignited without warning.
Now researchers at Rice University have come up with a solution to this very serious safety problem in the form of a combined electrolyte and separator for rechargeable lithium-ion batteries that supplies energy at usable voltages and in high temperatures. The material is a toothpaste-like composite that is capable of performing well at and withstanding high temperatures without combusting.
The problem with most current lithium-battery chemistries is that they present safety concerns when heated beyond 50C (122F) due to the electrolyte/separator combination used in them, explained Marco-Tulio Rodrigues, a Rice graduate student and one of the authors of a paper on the research published in Advanced Materials Science.
“The separator is usually a thin polymer film and may deform at high temperatures, causing a short circuit,” Rodrigues told Design News. “The electrolytes are based on organic solvents, which tend to boil at high temperatures, increasing the internal pressure of the cell. Although commercial batteries implement some protection mechanisms to avoid these problems, any damages to the cell case may potentially lead to ignition, since the electrolyte is also highly flammable.”
The work of the Rice team addresses both the issue of developing a separator that will not cause a short circuit and an electrolyte that doesn’t have the tendency to catch fire, he said.
The batteries made with the components they developed functioned as intended in temperatures of 50C (122F) for more than a month without losing efficiency, according to researchers. Moreover, test batteries consistently operated from room temperature to 150C (302F), setting one of the widest temperature ranges ever reported for such devices, they said.
To solve the electrolyte problem, researchers used solutions based on ionic liquids in the electrolytes, which have largely been proposed as substitutes for organic solvents in the electrolyte of lithium-ion batteries because they present a much higher thermal stability, Rodrigues explained.
“These chemicals are basically special salts with a very low melting point, in such a way that they are liquid at room temperatures,” he said. “They are completely nonflammable and they do not evaporate at all until they decompose, which occurs beyond 350C (662F).”
With the electrolyte situation solved, researchers turned their attention to finding a new separator, which they addressed with a material called hexagonal boron nitride, also known as white graphene.
Films of platinum only two atoms thick supported by graphene could enable fuel cell catalysts with unprecedented catalytic activity and longevity, according to a study published recently by researchers at the Georgia Institute of Technology.
Platinum is one of the most commonly used catalysts for fuel cells because of how effectively it enables the oxidation reduction reaction at the center of the technology. But its high cost has spurred research efforts to find ways to use smaller amounts of it while maintaining the samecatalytic activity.
“There’s always going to be an initial cost for producing a fuel cell withplatinum catalysts, and it’s important to keep that cost as low as possible,” said Faisal Alamgir, an associate professor in Georgia Tech’s School of Materials Science and Engineering. “But the real cost of a fuel cell system is calculated by how long that system lasts, and this is a question of durability.
“Recently there’s been a push to use catalytic systems withoutplatinum, but the problem is that there hasn’t been a system proposed so far that simultaneously matches the catalytic activity and the durability of platinum,” Alamgir said.
The Georgia Tech researchers tried a different strategy. In the study, which was published on September 18 in the journalAdvanced Functional Materialsand supported by the National Science Foundation, they describe creating several systems that used atomically-thinfilmsof platinum supported by a layer of graphene—effectively maximizing the total surface area of the platinum available for catalytic reactions and using a much smaller amount of the precious metal.
Most platinum-based catalytic systems use nanoparticles of the metal chemically bonded to a support surface, where surface atoms of the particles do most of the catalytic work, and the catalytic potential of the atoms beneath the surface is never utilized as fully as the surface atoms, if at all.
Additionally, the researchers showed that the new platinum films that are at least two atoms thick outperformed nanoparticle platinum in the dissociation energy, which is a measure of the energy cost of dislodging a surface platinum atom. That measurement suggests those films could make potentially longer-lasting catalytic systems.
To prepare the atomically-thin films, the researchers used a process called electrochemical atomic layer deposition to grow platinum monolayers on a layer of graphene, creating samples that had one, two or three atomic layers of atoms. The researchers then tested the samples for dissociation energy and compared the results to the energy of a single atom of platinum on graphene as well as the energy from a common configurations of platinum nanoparticles used in catalysts.
“The fundamental question at the heart of this work was whether it was possible that a combination of metallic andcovalent bondingcan render the platinum atoms in a platinum-graphene combination more stable than their counterparts in bulk platinum used commonly in catalysts that are supported by metallic bonding,” said Seung Soon Jang, an associate professor in the School of Materials Science and Engineering.
The researchers found that the bond between neighboring platinum atoms in the film essentially combines forces with the bond between the film and the graphene layer to provide reinforcement across the system. That was especially true in the platinum film that was two atoms thick.
“Typically metallic films below a certain thickness are not stable because the bonds between them are not directional, and they tend to roll over each other and conglomerate to form a particle,” Alamgir said. “But that’s not true with graphene, which is stable in a two-dimensional form, even one atom thick, because it has very strong covalent directional bonds between its neighboringatoms. So this new catalytic system could leverage the directional bonding of the graphene to support an atomically-thin film of platinum.”
Future research will involve further testing of how the films behave in a catalytic environment. The researchers found in earlier research on graphene-platinum films that the material behaves similarly in catalytic reactions regardless of which side—graphene or platinum—is the exposed active surface.
“In this configuration, the graphene is not acting as a separate entity from the platinum,” Alamgir said. “They’re working together as one. So we believe that if you’re exposing thegrapheneside, you get the same catalytic activity and you could further protect the platinum, potentially further enhancing durability.”
More information:Ji Il Choi et al, Contiguous and Atomically Thin Pt Film with Supra‐Bulk Behavior Through Graphene‐Imposed Epitaxy,Advanced Functional Materials(2019).DOI: 10.1002/adfm.201902274
Samsung phones will have super fast graphene, rather than lithium, batteries within the next two years.
According to leaker Evan Blass, Samsung is developing graphene batteries for its smartphones — and we could see the first ones arrive as soon as next year.
The reason for the change is clear: exceptionally fast charging. Reportedly a full charge will now take just half an hour on a graphene battery, and despite recent leaps forward in fast-charging that would still be a significant improvement on the standard lithium ion battery.
The news is the latest update we’ve heard since Samsung reported in 2017 that they had developed a graphene ball that could charge 5x faster than standard phone batteries (reported byCnet). So why is it taking so long for the batteries to make it onto the market? Blass surmises that’s it’s simply a question of economics: “they still need to raise capacities while lowering costs.” Once that balance is found, this tech innovation could be a true game changer.
This news comes shortly after the release of Samsung’s latest flagship phablet, theGalaxy Note 10. It boasts an impressive 3500mAh battery, while it’s big brother — theGalaxy Note 10 Plus — has a whopping capacity of 4300mAh. But they’re not just about batteries. While both run on the powerful Exynos 9825 chip, specifications diverge significantly. The Galaxy note 10 has an 6.3-inch 1080 x 2280 resolution screen, with 8GB of RAM and a triple camera set-up; meanwhile, the Galaxy Note 10 Plus has an even larger 6.8-inch screen with a sharper 1440 x 3040 resolution, 12GB of RAM, and its triple rear camera is complemented with a Time of Flight 3D sensor.
With all the recent innovations in smartphone batteries, from huge capacities to Qi wireless charging, you might have thought there was nowhere else to innovate. But graphene technology could point towards an era of even faster charging. All that’s left to be seen is how pricey is it, and whether the capacity will be enough to satisfy demanding users.
A graphene container system for manufacturing has been developed by GrapheneCA. The 40-foot containers are designed specifically for industrial producers and high-tech applications of graphene.
“It has developed a novel Mobile Graphene Container System (MGCS), the world’s first scalable, modular graphene production system, to help companies manufacture graphene in-house.
The New York-based company, which develops graphene-based technology for industries, said MGCS is available in 40-foot containers that are designed specifically for industrial producers and high-tech applications. The company said that with MGCS’ high quality, “ecologically clean graphene can be produced in-house” anywhere in the world.
“Think of Mobile Graphene Container System as your own graphene production line,” said David Robles, head of business development at GrapheneCA. “Producers will be able to secure a constant graphene supply and have greater control over their production volume and price.”
Robles said the process eliminates the reliance on “third-party suppliers and complicated logistics.”The industrial containers produce a high volume of industrial graphene in quantities of 4 tons of powder or more than 12 tons of graphene paste, said the company.
For high-tech applications, MGCS is able to produce pure graphene and graphene oxides derivatives, a much finer quality of product. The manufactured products have additional drying and quality-control features that reduce the need for graphene experts.
The company said that the next generation method simplifies graphene production and addresses problems that crop up during product shipments.
Graphene shipping is filled with complications due to the material being a highly voluminous compound, greatly limiting the amount of product that can be stored in a shipping container. MGCS allows for a clever work-around whereby ecologically clean graphene can be produced in-house by a company eliminating high shipping costs. Production only needs a water source and electric, diesel or bio-diesel power.”
Researchers have created an ink made of graphene nanosheets, and demonstrated that the ink can be used to print 3-D structures. As the graphene-based ink can be mass-produced in an inexpensive and environmentally friendly manner, the new methods pave the way toward developing a wide variety of printable energy storage devices.
The researchers, led by Jingyu Sun and Zhongfan Liu at Soochow University and the Beijing Graphene Institute, and Ya-yun Li at Shenzhen University, have published a paper on their work in a recent issue ofACS Nano.
“Our work realizes the scalable and green synthesis of nitrogen-dopedgraphenenanosheets on a salt template by direct chemical vapor deposition,” Sun toldPhys.org. “This allows us to further explore thus-derived inks in the field of printable energy storage.”
As the scientists explain, a key goal in graphene research is the mass production of graphene with high quality and at low cost. Energy-storage applications typically require graphene in powder form, but so far production methods have resulted in powders with a large number of structural defects and chemical impurities, as well as nonuniform layer thickness. This has made it difficult to prepare high-quality graphene inks.
In the new paper, the researchers have demonstrated a new method for preparing graphene inks that overcomes these challenges. The method involves growing nitrogen-doped graphene nanosheets over NaCl crystals using direct chemical vapor deposition, which causes molecular fragments of nitrogen and carbon to diffuse on the surface of the NaCl crystals. The researchers chose NaCl due to its natural abundance and low cost, as well as its water solubility.
To remove the NaCl, the coated crystals are submerged in water, which causes the NaCl to dissolve and leave behind pure nitrogen-doped graphene cages. In the final step, treating the cages with ultrasound transforms the cages into 2-D nanosheets, each about 5-7 graphite layers thick.
The resulting nitrogen-doped graphene nanosheets have relatively few defects and an ideal size (about 5 micrometers in side length) for printing, as larger flakes can block the nozzle.
To demonstrate the nanosheets’ effectiveness, the researchers printed a wide variety of 3-D structures using inks based on the graphene sheets.
Among their demonstrations, the researchers used the ink as a conductive additive for anelectrode material(vanadium nitride) and used the composite ink to print flexible electrodes for supercapacitors with high power density and good cyclic stability.
In a second demonstration, the researchers created a composite ink made of the graphene sheets along with binder material (polypropylene) for printing interlayers for Li−S batteries.
Compared to batteries with separators made only of the conventional material, those made with the composite material exhibited enhanced conductivity, leading to an overall improvement in battery performance.
“In the future, we plan to exploit the directchemical vapor depositiontechnique for the mass production of high-quality graphene powders toward emerging printable energy storage applications,” Sun said.
More information:Nan Wei et al. “Scalable Salt-Templated Synthesis of Nitrogen-Doped Graphene Nanosheets toward Printable Energy Storage.”ACS Nano. DOI:10.1021/acsnano.9b03157
Only 30% of all freshwater on the planet is not locked up in ice caps or glaciers (not for much longer, though). Of that, some 20% is in areas too remote for humans to access and of the remaining 80% about three-quarters comes at the wrong time and place – in monsoons and floods – and is not always captured for use by people. The remainder is less than 0.08 of 1% of the total water on the planet (read more: “Nanotechnology and water treatment“)
An abundance of water equivalent to about 10% of the total freshwater in lakes exists in the earth atmosphere, which can be a non-negligible freshwater resource to fight against the water shortage.
That’s where the graphene nanocomposite foam comes in: The foam realizes water harvesting through a capture-release cycle:
1) the capture process is composed of moisture adsorption from air by lithium chloride (LiCl) and water preservation by poly(vinyl alcohol) (PVA) and
2) the release relies on the solar-to-thermal transformer, reduced graphene oxide (rGO), to facilitate evaporation. In addition, polyimide is employed as a substrate material for the purpose of 3D porous structure formation and mechanical property enhancement.
Photograph, schematic diagram, and SEM images of the graphene nanocomposite foam. (a) Photograph of the graphene nanocomposite foam. (b) Schematic diagram of the graphene nanocomposite foam. Foam was prepared through a three-step process: freeze-drying, thermal annealing, and hydrophilic treatment. rGO/PI nanosheet, as the basic unit, can achieve the water harvesting capture-release cycle without additional energy input. (c) SEM image presents a porous structure of the rGO/PI foam without hydrophilic treatment. (d) Magnified SEM image of the rGO/PI foam without hydrophilic treatment to show a relatively smooth surface of the nanosheet. (e) SEM image of the graphene nanocomposite foam after hydrophilic treatment. (f) Magnified SEM image of the hydrophilic rGO/PI foam with bumped nanostructures. (g) Schematic diagram of the water vapor capture-release cycle.
LiCl and PVA were responsible for the water capture and water storage, respectively. Adsorbed water was stored as crystallized water in LiCl hydrates and the free water molecules were restrained by hydroxyl groups on PVA through the hydrogen bond, which led to the transformation of the nanosheet from dry status to wet status. Opposite procedure, from wet status to dry status, was realized by the rGO converting the solar energy to thermal energy to facilitate water evaporation under irradiation. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
The as-fabricated foam can adsorb water up to 2.87 g per gram in 24 hours at a relative humidity of 90% and a temperature of 30°C, and release almost all the uptake water when it is exposed under a flux of 1 sun (1000 W per square meter, equal to the light intensity of natural sunlight) for 3 hours.
At the same time, the functional foam shows superelasticity, lightweight, and remarkable reusability, thus revealing its possibility to practical use.
The researchers write that, even though the rGO/PI nanocomposite foam can harvest freshwater from air, it is essential to enhance water harvesting efficiency.
“Another big challenge impedes the water harvesting system utilization to explore a more cost-effective way to prepare the products,” they conclude. “Though the three-step synthesis method and the composition of the foam have been optimized, it is still necessary to reduce the cost and increase the fabrication efficiency. Meanwhile, environmentally friendly materials are recommended, which would take the water harvesting system one step further to commercial application and large-scale production.”
†CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-Nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China
‡School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
§Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning, Guangxi 530004, P. R. China
Lithium batteries are what allow electric vehicles to travel several hundred miles on one charge. Their capacity for energy storage is well known, but so is their tendency to occasionally catch on fire—an occurrence known to battery researchers as “thermal runaway.” These fires occur most frequently when the batteries overheat or cycle rapidly. With more and more electric vehicles on the road each year, battery technology needs to adapt to reduce the likelihood of these dangerous and catastrophic fires.
Researchers from the University of Illinois at Chicago College of Engineering report that graphene—wonder material of the 21st century—may take the oxygen out of lithium battery fires. They report their findings in the journal Advanced Functional Materials.
The reasons lithium batteries catch fire include rapid cycling or charging and discharging, and high temperatures in the battery. These conditions can cause the cathode inside the battery—which in the case of most lithium batteries is a lithium-containing oxide, usually lithium cobalt oxide—to decompose and release oxygen. If the oxygen combines with other flammable products given off through decomposition of the electrolyte under high enough heat, spontaneous combustion can occur.
“We thought that if there was a way to prevent the oxygen from leaving the cathode and mixing with other flammable products in the battery, we could reduce the chances of a fire occurring,” said Reza Shahbazian-Yassar, associate professor of mechanical and industrial engineering in the UIC College of Engineering and corresponding author of the paper.
It turns out that a material Shahbazian-Yassar is very familiar with provided a perfect solution to this problem. That material is graphene—a super-thin layer of carbon atoms with unique properties. Shahbazian-Yassar and his colleagues previously had used graphene to help modulate lithium buildup on electrodes in lithium metal batteries.
Lithium cobalt oxide particles coated in graphene. Credit: Reza Shahbazian-Yassar.
Shahbazian-Yassar and his colleagues knew that graphene sheets are impermeable to oxygen atoms. Graphene is also strong, flexible and can be made to be electrically conductive. Shahbazian-Yassar and Soroosh Sharifi-Asl, a graduate student in mechanical and industrial engineering at UIC and lead author of the paper, thought that if they wrapped very small particles of the lithium cobalt oxide cathode of a lithium battery in graphene, it might prevent oxygen from escaping.
First, the researchers chemically altered the graphene to make it electrically conductive. Next, they wrapped the tiny particles of lithium cobalt oxide cathode electrode in the conductive graphene.
When they looked at the graphene-wrapped lithium cobalt oxide particles using electron microscopy, they saw that the release of oxygen under high heat was reduced significantly compared with unwrapped particles.
Next, they bound together the wrapped particles with a binding material to form a usable cathode, and incorporated it into a lithium metal battery. When they measured released oxygen during battery cycling, they saw almost no oxygen escaping from cathodes even at very high voltages. The lithium metal battery continued to perform well even after 200 cycles.
“The wrapped cathode battery lost only about 14% of its capacity after rapid cycling compared to a conventional lithium metal battery where performance was down about 45% under the same conditions,” Sharifi-Asl said.
“Graphene is the ideal material for blocking the release of oxygen into the electrolyte,” Shahbazian-Yassar said. “It is impermeable to oxygen, electrically conductive, flexible, and is strong enough to withstand conditions within the battery. It is only a few nanometers thick so there would be no extra mass added to the battery. Our research shows that its use in the cathode can reliably reduce the release of oxygen and could be one way that the risk for fire in these batteries—which power everything from our phones to our cars—could be significantly reduced.”