Graphene-MoS2 Hybrid Material for Energy Storage and Transfer Applications



The exponential growth rates of population density and the worldwide economy has required a significant investment in energy storage devices, particularly those which are portable and can be used for future flexible electronics.

To meet the increasing energy demands of a growing population, not only are new ways of creating the energy being devised, but so are new ways of storing this that energy. 

A team of Researchers from India have developed a hybrid nanomaterial composed of graphene and flower-shaped MoS2 nanostructures to store energy in a prototype supercapacitor.



As a result of an ever-expanding population and its associated energy consumption, there is a projection that the demand for energy in 2050 will exceed 40 terawatts (TW). 




Because of the requirements for a high amount of energy, new ways of producing renewable energy are being researched and implemented, as current non-renewable fuels will eventually run out.

Due to both the energy increase and nature of the produced energy, new materials are also being developed that can store this energy efficiently.

At present, such storage capabilities are not even close to meeting the energy demands set out in future predictions. Current devices can only store 1% of renewable energy that storage devices do for fossil fuels.

As such, there is a great need to not only create materials which can store renewable energy, but to also produce materials with a real-world function that can rival non-renewable storage options, potentially as a variant of Li-ion and Na-air batteries that can hold renewable-produced energy.



The team of Researchers have created a hybrid nanomaterial composed of flower-like MoS2 nanostructures and 3D graphene heterostructures to be used as an active material in energy storage and transfer devices.
 

The Researchers also tested and employed the material in a solid-state supercapacitor, where the 3D graphene-MoS2 material was used with a graphite current collector.

To create the active material, the Researchers first created MoS2 nanospheres through a hydrothermal method using ammonium molybdate and thiourea. 

A modified hydrothermal method was then utilized to deposit 3D graphene oxide onto a graphite electrode using a series of wet synthetic steps.

The MoS2 nanostructures were then also deposited onto the graphene sheets. To create the supercapacitor, the Researchers, alongside the electrodes, used a polyvinyl acetate (PVA) gel and a gel-soaked whatman filter paper as part of the internal components. A drying time of 12 hours was required for the device to be fully fabricated.

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Nanogels for heart attack patients: Getting to the “heart” of the matter


heart of the matter 59c23972eebce

Heart disease and heart-related illnesses are a leading cause of death around the world, but treatment options are limited. Now, one group reports in ACS Nano that encapsulating stem cells in a nanogel could help repair damage to the heart.

Myocardial infarction, also known as a heart attack, causes damage to the muscular walls of the heart. Scientists have tried different methods to repair this damage. For example, one method involves directly implanting stem cells in the heart wall, but the cells often don’t take hold, and sometimes they trigger an immune reaction. Another treatment option being explored is injectable hydrogels, substances that are composed of water and a polymer. Naturally occurring polymers such as keratin and collagen have been used but they are expensive, and their composition can vary between batches. So Ke Cheng, Hu Zhang, Jinying Zhang and colleagues wanted to see whether placing stem cells in inexpensive hydrogels with designed tiny pores that are made in the laboratory would work.

The team encapsulated stem cells in nanogels, which are initially liquid but then turn into a soft gel when at body temperature. The nanogel didn’t adversely affect stem cell growth or function, and the encased stem cells didn’t trigger a rejection response. When these enveloped cells were injected into mouse and pig hearts, the researchers observed increased cell retention and regeneration compared to directly injecting just the stem cells.

In addition, the heart walls were strengthened. Finally, the group successfully tested the encapsulated  in mouse and pig models of .

 Explore further: Cardiac stem cells from heart disease patients may be harmful

More information: “Heart Repair Using Nanogel-Encapsulated Human Cardiac Stem Cells in Mice and Pigs with Myocardial Infarction” ACS Nano (2017). pubs.acs.org/doi/abs/10.1021/acsnano.7b01008

 

Researchers make atoms-thick Post-It notes for solar cells and circuits: U of Chicago


23-scientistsmaSchematic diagram (left) and electron microscope image (right) of a stacked set of semiconductor films, made using the Park lab’s new technique. Credit: Park et. al./Nature

Over the past half-century, scientists have shaved silicon films down to just a wisp of atoms in pursuit of smaller, faster electronics. For the next set of breakthroughs, though, they’ll need novel ways to build even tinier and more powerful devices.

A study led by UChicago researchers, published Sept. 20 in Nature, describes an innovative method to make stacks of semiconductors just a few atoms thick. The technique offers scientists and engineers a simple, cost-effective method to make thin, uniform layers of these materials, which could expand capabilities for devices from solar cells to cell phones.

Stacking thin layers of materials offers a range of possibilities for making  with unique properties. But manufacturing such  is a delicate process, with little room for error.

“The scale of the problem we’re looking at is, imagine trying to lay down a flat sheet of plastic wrap the size of Chicago without getting any  in it,” said Jiwoong Park, a UChicago professor with the Department of Chemistry, the Institute for Molecular Engineering and the James Franck Institute, who led the study. “When the material itself is just atoms thick, every little stray atom is a problem.”

Today, these layers are “grown” instead of stacking them on top of one another. But that means the bottom layers have to be subjected to harsh growth conditions such as high temperatures while the new ones are added—a process that limits the materials with which to make them.

Park’s team instead made the films individually. Then they put them into a vacuum, peeled them off and stuck them to one another, like Post-It notes. This allowed the scientists to make films that were connected with weak bonds instead of stronger covalent bonds—interfering less with the perfect surfaces between the layers.

“The films, vertically controlled at the atomic-level, are exceptionally high-quality over entire wafers,” said Kibum Kang, a postdoctoral associate who was the first author of the study.

Kan-Heng Lee, a graduate student and co-first author of the study, then tested the films’ electrical properties by making them into devices and showed that their functions can be designed on the atomic scale, which could allow them to serve as the essential ingredient for future computer chips.

The method opens up a myriad of possibilities for such films. They can be made on top of water or plastics; they can be made to detach by dipping them into water; and they can be carved or patterned with an ion beam. Researchers are exploring the full range of what can be done with the method, which they said is simple and cost-effective.

“We expect this new  to accelerate the discovery of novel , as well as enabling large-scale manufacturing,” Park said.

 Explore further: A simple additive to improve film quality

More information: “Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures,” Kang et. al, Nature, Sept. 20. DOI: 10.1038/nature23905

 

Graphene and other carbon Nanomaterials can Replace Scarce Metals


Graphene Scarce Metals 170919091029_1_540x360

Scarce metals are found in a wide range of everyday objects around us. They are complicated to extract, difficult to recycle and so rare that several of them have become “conflict minerals” which can promote conflicts and oppression. New research shows that there are potential technology-based solutions that can replace many of the metals with carbon nanomaterials, such as graphene.

Scarce metals are found in a wide range of everyday objects around us. They are complicated to extract, difficult to recycle and so rare that several of them have become “conflict minerals” which can promote conflicts and oppression. A survey at Chalmers University of Technology now shows that there are potential technology-based solutions that can replace many of the metals with carbon nanomaterials, such as graphene.

They can be found in your computer, in your mobile phone, in almost all other electronic equipment and in many of the plastics around you. Society is highly dependent on scarce metals, and this dependence has many disadvantages.

Scarce metals such as tin, silver, tungsten and indium are both rare and difficult to extract since the workable concentrations are very small. This ensures the metals are highly sought after — and their extraction is a breeding ground for conflicts, such as in the Democratic Republic of the Congo where they fund armed conflicts.

In addition, they are difficult to recycle profitably since they are often present in small quantities in various components such as electronics.

Rickard Arvidsson and Björn Sandén, researchers in environmental systems analysis at Chalmers University of Technology, have now examined an alternative solution: substituting carbon nanomaterials for the scarce metals. These substances — the best known of which is graphene — are strong materials with good conductivity, like scarce metals.

“Now technology development has allowed us to make greater use of the common element carbon,” says Sandén. “Today there are many new carbon nanomaterials with similar properties to metals. It’s a welcome new track, and it’s important to invest in both the recycling and substitution of scarce metals from now on.”

The Chalmers researchers have studied the main applications of 14 different metals, and by reviewing patents and scientific literature have investigated the potential for replacing them by carbon nanomaterials. The results provide a unique overview of research and technology development in the field.

According to Arvidsson and Sandén the summary shows that a shift away from the use of scarce metals to carbon nanomaterials is already taking place.

“There are potential technology-based solutions for replacing 13 out of the 14 metals by carbon nanomaterials in their most common applications. The technology development is at different stages for different metals and applications, but in some cases such as indium and gallium, the results are very promising,” Arvidsson says.

“This offers hope,” says Sandén. “In the debate on resource constraints, circular economy and society’s handling of materials, the focus has long been on recycling and reuse. Substitution is a potential alternative that has not been explored to the same extent and as the resource issues become more pressing, we now have more tools to work with.”

The research findings were recently published in the Journal of Cleaner Production. Arvidsson and Sandén stress that there are significant potential benefits from reducing the use of scarce metals, and they hope to be able to strengthen the case for more research and development in the field.

“Imagine being able to replace scarce metals with carbon,” Sandén says. “Extracting the carbon from biomass would create a natural cycle.”

“Since carbon is such a common and readily available material, it would also be possible to reduce the conflicts and geopolitical problems associated with these metals,” Arvidsson says.

At the same time they point out that more research is needed in the field in order to deal with any new problems that may arise if the scarce metals are replaced.

“Carbon nanomaterials are only a relatively recent discovery, and so far knowledge is limited about their environmental impact from a life-cycle perspective. But generally there seems to be a potential for a low environmental impact,” Arvidsson says.

Facts:

Carbon nanomaterials consist solely or mainly of carbon, and are strong materials with good conductivity. Several scarce metals have similar properties. The metals are found, for example, in cables, thin screens, flame-retardants, corrosion protection and capacitors.

Rickard Arvidsson and Björn Sandén at Chalmers University of Technology have investigated whether the carbon nanomaterials graphene, fullerenes and carbon nanotubes have the potential to replace 14 scarce metals in their main areas of application (see table in attached image). They found potential technology-based solutions to replace the metals with carbon nanomaterials for all applications except for gold in jewellery. The metals which we are closest to being able to substitute are indium, gallium, beryllium and silver.

Story Source:

Materials provided by Chalmers University of TechnologyNote: Content may be edited for style and length.


Journal Reference:

  1. Rickard Arvidsson, Björn A. Sandén. Carbon nanomaterials as potential substitutes for scarce metalsJournal of Cleaner Production, 2017; 156: 253 DOI: 10.1016/j.jclepro.2017.04.048

Solar-to-Fuel System Recycles CO2 to Make Ethanol and Ethylene: Berkeley National Lab



Schematic of a solar-powered electrolysis cell which converts carbon dioxide into hydrocarbon and oxygenate products with an efficiency far higher than natural photosynthesis. Power-matching electronics allow the system to operate over a range of sun conditions. (Credit: Clarissa Towle/Berkeley Lab)

Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis

Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have harnessed the power of photosynthesis to convert carbon dioxide into fuels and alcohols at efficiencies far greater than plants. The achievement marks a significant milestone in the effort to move toward sustainable sources of fuel.

Many systems have successfully reduced carbon dioxide to chemical and fuel precursors, such as carbon monoxide or a mix of carbon monoxide and hydrogen known as syngas. This new work, described in a study published in the journal Energy and Environmental Science, is the first to successfully demonstrate the approach of going from carbon dioxide directly to target products, namely ethanol and ethylene, at energy conversion efficiencies rivaling natural counterparts.

The researchers did this by optimizing each component of a photovoltaic-electrochemical system to reduce voltage loss, and creating new materials when existing ones did not suffice.

“This is an exciting development,” said study principal investigator Joel Ager, a Berkeley Lab scientist with joint appointments in the Materials Sciences and the Chemical Sciences divisions. “As rising atmospheric CO2 levels change Earth’s climate, the need to develop sustainable sources of power has become increasingly urgent. Our work here shows that we have a plausible path to making fuels directly from sunlight.”

That sun-to-fuel path is among the key goals of the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub established in 2010 to advance solar fuel research. The study was conducted at JCAP’s Berkeley Lab campus.

The initial focus of JCAP research was tackling the efficient splitting of water in the photosynthesis process. Having largely achieved that task using several types of devices, JCAP scientists doing solar-driven carbon dioxide reduction began setting their sights on achieving efficiencies similar to those demonstrated for water splitting, considered by many to be the next big challenge in artificial photosynthesis.

Another research group at Berkeley Lab is tackling this challenge by focusing on a specific component in a photovoltaic-electrochemical system. In a study published today, they describe a new catalyst that can achieve carbon dioxide to multicarbon conversion using record-low inputs of energy.

Not just for noon


For this JCAP study, researchers engineered a complete system to work at different times of day, not just at a light energy level of 1-sun illumination, which is equivalent to the peak of brightness at high noon on a sunny day. They varied the brightness of the light source to show that the system remained efficient even in low light conditions.

When the researchers coupled the electrodes to silicon photovoltaic cells, they achieved solar conversion efficiencies of 3 to 4 percent for 0.35 to 1-sun illumination. Changing the configuration to a high-performance, tandem solar cell connected in tandem yielded a conversion efficiency to hydrocarbons and oxygenates exceeding 5 percent at 1-sun illumination.

Copper-Silver Cathode

At left is a surface view of a bimetallic copper-silver nanocoral cathode taken from a scanning electron micrograph. To the right is an energy-dispersive X-ray image of the cathode with the copper (in pink/red) and silver (in green) highlighted. (Credit: Gurudayal/Berkeley Lab)

“We did a little dance in the lab when we reached 5 percent,” said Ager, who also holds an appointment as an adjunct professor at UC Berkeley’s Materials Science and Engineering Department.

Among the new components developed by the researchers are a copper-silver nanocoral cathode, which reduces the carbon dioxide to hydrocarbons and oxygenates, and an iridium oxide nanotube anode, which oxidizes the water and creates oxygen.

“The nice feature of the nanocoral is that, like plants, it can make the target products over a wide range of conditions, and it is very stable,” said Ager.

The researchers characterized the materials at the National Center for Electron Microscopy at the Molecular Foundry, a DOE Office of Science User Facility at Berkeley Lab. The results helped them understand how the metals functioned in the bimetallic cathode. Specifically, they learned that silver aids in the reduction of carbon dioxide to carbon monoxide, while the copper picks up from there to reduce carbon monoxide further to hydrocarbons and alcohols.

Seeking better, low-energy breakups



Because carbon dioxide is a stubbornly stable molecule, breaking it up typically involves a significant input of energy.
“Reducing CO2 to a hydrocarbon end product like ethanol or ethylene can take up to 5 volts, start to finish,” said study lead author Gurudayal, postdoctoral fellow at Berkeley Lab. “Our system reduced that by half while maintaining the selectivity of products.”

Notably, the electrodes operated well in water, a neutral pH environment.

“Research groups working on anodes mostly do so using alkaline conditions since anodes typically require a high pH environment, which is not ideal for the solubility of CO2,” said Gurudayal. “It is very difficult to find an anode that works in neutral conditions.”

The researchers customized the anode by growing the iridium oxide nanotubes on a zinc oxide surface to create a more uniform surface area to better support chemical reactions.

“By working through each step so carefully, these researchers demonstrated a level of performance and efficiency that people did not think was possible at this point,” said Berkeley Lab chemist Frances Houle, JCAP deputy director for Science and Research Integration, who was not part of the study. “This is a big step forward in the design of devices for efficient CO2 reduction and testing of new materials, and it provides a clear framework for the future advancement of fully integrated solar-driven CO2-reduction devices.”

Other co-authors on the study include James Bullock, a Berkeley Lab postdoctoral researcher in materials sciences, who was instrumental in engineering the system’s photovoltaic and electrolysis cell pairing. Bullock works in the lab of study co-author Ali Javey, Berkeley Lab senior faculty scientist and a UC Berkeley professor of electrical engineering and computer sciences.

This work is supported by the DOE Office of Science.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. 
The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Graphene-wrapped nanocrystals may open door toward next-gen fuel cells



Ultra-Thin  oxide layer (oxygen atoms shown in red) coating graphene-wrapped magnesium nanoparticles (orange) still allows in hydrogen atoms (blue) for hydrogen storage applications

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory have developed a mix of metal nanocrystals wrapped in graphene that may open the door to the creation of a new type of fuel cell by enabling enhanced hydrogen storage properties.

Graphene-Wrapped Nanocrystals Make Inroads Toward Next-Gen Fuel Cells



Ultra-thin oxide layer (oxygen atoms shown in red) coating graphene-wrapped magnesium nanoparticles (orange) still allows in hydrogen atoms (blue) for hydrogen storage applications

The team studied how graphene can be used as both selective shielding, as well as a performance increasing factor in terms of hydrogen storage. 

The study drew upon a range of Lab expertise and capabilities to synthesize and coat the magnesium crystals, which measure only 3-4 nanometers (billionths of a meter) across; study their nanoscale chemical composition with X-rays; and develop computer simulations and supporting theories to better understand how the crystals and their carbon coating function together.

Reduced graphene oxide (or rGO) has nanoscale holes that permit hydrogen to pass through while keeping larger molecules away. This carbon wrapping was intended to prevent the magnesium – which is used as a hydrogen storage material – from reacting with its environment, including oxygen, water vapor and carbon dioxide. 

Such exposures could produce a thick coating of oxidation that would prevent the incoming hydrogen from accessing the magnesium surfaces. 

The study, however, suggests that an atomically thin layer of oxidation did form on the crystals during their preparation. Surprisingly, this oxide layer doesn’t seem to degrade the material’s performance.

The study’s lead author stated “Most people would suspect that the oxide layer is bad news for hydrogen storage, which it turns out may not be true in this case. Without this oxide layer, the reduced graphene oxide would have a fairly weak interaction with the magnesium, but with the oxide layer the carbon-magnesium binding seems to be stronger. 

That’s a benefit that ultimately enhances the protection provided by the carbon coating. There doesn’t seem to be any downside”.

The researchers noted that the current generation of hydrogen-fueled vehicles power their fuel cell engines using compressed hydrogen gas. “This requires bulky, heavy cylindrical tanks that limit the driving efficiency of such cars”, and the nanocrystals offer one possibility for eliminating these bulky tanks by storing hydrogen within other materials.

Ionic Industries announces a process for economically mass-producing graphene micro supercapacitors



Ionic Industries recently announced a process for economically mass-producing graphene micro supercapacitors and added that its directors and key personnel have taken direct stakes in the company.

Ionic Industries’ graphene supercapacitors patent image




Ionic stated that since it published the positive results on its graphene micro planar supercapacitors 2 years before, the company has been working toward developing a device that not only demonstrates similar performance but can be produced at scale to deliver an economically viable device.

The last 2 years of work reportedly culminated in the filing of a new patent titled: Capacitive energy storage device and method of producing same (Australian Provisional Patent Application 2017903619). 

The new patent covers: the design of new energy storage device, being a planar micro supercapacitor printed on a porous film; Ionic’s technique of stacking multiple layers of planar supercapacitors to create a 3D device that has ground-breaking energy and power density characteristics; and, most importantly, the company’s method for printing these devices so that they can be mass produced at low cost.

The critical element in this new technology is the ability to print the supercapacitors in the 1000s per minute, rather than individually creating each device with an expensive, direct-write approaches using lasers or ion beams. The technology builds on Ionic’s existing patent relating to graphene oxide membranes and it means the company could create these devices as easily as factories today produce food packaging and labels using gravure printers.

The team is now working on assembling the prototype device which is scheduled for completion in the next 6 weeks before it go into trials for a period of several months. 
The expected end result is a supercapacitor energy storage device comprised of printed graphene micro planar supercapacitors that can be produced economically at scale.

Ionic stated that it is extremely excited about this development as it brings it well within sight of a commercial product. The next steps involve identifying appropriate, world leading partners with whom Ionic can introduce this technology into products such as medical devices, wearable technologies, IoT devices or remote sensing applications.

More Durable – Less Expensive Fuel Cells Speeds the Commercialization of FC Vehicles – U. of Delaware


vehicles-cars-hydrogen-fuel-cellResearchers have developed a new technology that could speed up the commercialization of fuel cell vehicles

Summary: A new technology has been created that could make fuel cells cheaper and more durable. Hydrogen-powered fuel cells are a green alternative to internal combustion engines because they produce power through electro-chemical reactions, leaving no pollution behind. Platinum is the most common catalyst in the type of fuel cells used in vehicles, but it’s expensive. The UD team used a novel method to come up with a less expensive catalyst.

A team of engineers at the University of Delaware has developed a technology that could make fuel cells cheaper and more durable, a breakthrough that could speed up the commercialization of fuel cell vehicles.

They describe their results in a paper published in Nature Communications.

Hydrogen-powered fuel cells are a green alternative to internal combustion engines because they produce power through electrochemical reactions, leaving no pollution behind.

Materials called catalysts spur these electro-chemical reactions. Platinum is the most common catalyst in the type of fuel cells used in vehicles.F Cell Car images

However, platinum is expensive — as anyone who’s shopped for jewelry knows. The metal costs around $30,000 per kilogram.

Instead, the UD team made a catalyst of tungsten carbide, which goes for around $150 per kilogram. They produced tungsten carbide nanoparticles in a novel way, much smaller and more scalable than previous methods.

“The material is typically made at very high temperatures, about 1,500 Celsius, and at these temperatures, it grows big and has little surface area for chemistry to take place on,” said Dionisios Vlachos, director of UD’s Catalysis Center for Energy Innovation.. “Our approach is one of the first to make nanoscale material of high surface area that can be commercially relevant for catalysis.”

The researchers made tungsten carbide nanoparticles using a series of steps including hydrothermal treatment, separation, reduction, carburization and more.

“We can isolate the individual tungsten carbide nanoparticles during the process and make a very uniform distribution of particle size,” said Weiqing Zheng, a research associate at the Catalysis Center for Energy Innovation.

Next, the researchers incorporated the tungsten carbide nanoparticles into the membrane of a fuel cell. Automotive fuel cells, known as proton exchange membrane fuel cells (PEMFCs), contain a polymeric membrane. This membrane separates the cathode from the anode, which splits hydrogen (H2) into ions (protons) and delivers them to the cathode, which puts out current.

The plastic-like membrane wears down over time, especially if it undergoes too many wet/dry cycles, which can happen easily as water and heat are produced during the electrochemical reactions in fuel cells.

When tungsten carbide is incorporated into the fuel cell membrane, it humidifies the membrane at a level that optimizes performance.

“The tungsten carbide catalyst improves the water management of fuel cells and reduces the burden of the humidification system,” said Liang Wang, an associate scientist in the Department of Mechanical Engineering.

The team also found that tungsten carbide captures damaging free radicals before they can degrade the fuel cell membrane. As a result, membranes with tungsten carbide nanoparticles last longer than traditional ones.

“The low-cost catalyst we have developed can be incorporated within the membrane to improve performance and power density,” said . “As a result, the physical size of the fuel cell stack can be reduced for the same power, making it lighter and cheaper. Furthermore, our catalyst is able to deliver higher performance without sacrificing durability, which is a big improvement over similar efforts by other groups.”

The UD research team used innovative methods to test the durability of a fuel cell made with tungsten carbide. They used a scanning electron microscope and focused ion beam to obtain thin-slice images of the membrane, which they analyzed with software, rebuilding the three-dimensional structure of the membranes to determine fuel cell longevity.

The group has applied for a patent and hopes to commercialize their technology.

“This is a very good example of how different groups across departments can collaborate,” Zheng said.

Story Source:

Materials

provided by University of DelawareNote: Content may be edited for style and length.


Journal Reference:

  1. Weiqing Zheng, Liang Wang, Fei Deng, Stephen A. Giles, Ajay K. Prasad, Suresh G. Advani, Yushan Yan, Dionisios G. Vlachos. Durable and self-hydrating tungsten carbide-based composite polymer electrolyte membrane fuel cellsNature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-00507-6

Supercharging Silicon Batteries – Powering Up LI Batteries


super silicon LI batt anode 170906103638_1_540x360
The porosity of the nano-structured Tantalum (in black) enables the formation of silicon channels (in blue) allowing lithium ions to travel faster within the battery. The rigidity of the tantalum scaffold also limits the expansion of the silicon and preserve structural integrity. Credit: Okinawa Institute of Science and Technology Graduate University Nanoparticles by Design Unit

Scientists have designed a novel silicon-based anode to provide lithium batteries with increased power and better stability.

 

As the world shifts towards renewable energy, moving on from fossil fuels, but at the same time relying on ever more energy-gobbling devices, there is a fast-growing need for larger high-performance batteries. Lithium-ion batteries (LIBs) power most of our portable electronics, but they are flammable and can even explode, as it happened to a recent model of smartphone. To prevent such accidents, the current solution is to encapsulate the anode — which is the negative (-) electrode of the battery, opposite to the cathode (+) — into a graphite frame, thus insulating the lithium ions. However, such casing is limited to a small scale to avoid physical collapse, therefore restraining the capacity — the amount of energy you can store — of the battery.

Looking for better materials, silicon offers great advantages over carbon graphite for lithium batteries in terms of capacity. Six atoms of carbon are required to bind a single atom of lithium, but an atom of silicon can bind four atoms of lithium at the same time, multiplying the battery capacity by more than 10-fold. However, being able to capture that many lithium ions means that the volume of the anode swells by 300% to 400%, leading to fracturing and loss of structural integrity. To overcome this issue, OIST researchers have now reported in Advanced Science the design of an anode built on nanostructured layers of silicon — not unlike a multi-layered cake — to preserve the advantages of silicon while preventing physical collapse.

This new battery is also aiming to improve power, which is the ability to charge and deliver energy over time.

“The goal in battery technology right now is to increase charging speed and power output,” explained Dr. Marta Haro Remon, first author of the study. “While it is fine to charge your phone or your laptop over a long period of time, you would not wait by your electric car for three hours at the charging station.”

And when it comes to providing energy, you would want your car to start off quickly at a traffic light or a stop sign, requiring a high spike in power, rather than slowly creeping forward. A well-thought design of a silicone-based anode might be a solution and answer these expectations.img_0132-3

The idea behind the new anode in the Nanoparticles by Design Unit at the Okinawa Institute of Science and Technology Graduate University is the ability to precisely control the synthesis and the corresponding physical structure of the nanoparticles. Layers of unstructured silicon films are deposited alternatively with tantalum metal nanoparticle scaffolds, resulting in the silicon being sandwiched in a tantalum frame.

“We used a technique called Cluster Beam Deposition,” continued Dr. Haro. “The required materials are directly deposited on the surface with great control. This is a purely physical method, there are no need for chemicals, catalysts or other binders.”

“We used a technique called Cluster Beam Deposition,” continued Dr. Haro. “The required materials are directly deposited on the surface with great control. This is a purely physical method, there are no need for chemicals, catalysts or other binders.”

The outcome of this research, led by Prof. Sowwan at OIST, is an anode with higher power but restrained swelling, and excellent cyclability — the amount of cycles in which a battery can be charged and discharged before losing efficiency. By looking closer into the nanostructured layers of silicon, the scientists realized the silicon shows important porosity with a grain-like structure in which lithium ions could travel at higher speeds compared to unstructured, amorphous silicon, explaining the increase in power. At the same time the presence of silicon channels along the Ta nanoparticle scaffolds allows the lithium ions to diffuse in the entire structure. On the other hand, the tantalum metal casing, while restraining swelling and improving structural integrity, also limited the overall capacity — for now.

However, this design is currently only at the stage of proof-of-concept, opening the door to numerous opportunities to improve capacity along with the increased power.

“It is a very open synthesis approach, there are many parameters you can play around,” commented Dr. Haro. “For example, we want to optimize the numbers of layers, their thickness, and replace tantalum metal with other materials.”

With this technique paving the way, it might very well be that the solution for future batteries, forecast to be omnipresent in our lives, will be found in nanoparticles.

Story Source:

 

Material provided by Okinawa Institute of Science and Technology (OIST) Graduate UniversityNote: Content may be edited for style and length.

Journal Reference:

  1. Marta Haro, Vidyadhar Singh, Stephan Steinhauer, Evropi Toulkeridou, Panagiotis Grammatikopoulos, Mukhles Sowwan. Nanoscale Heterogeneity of Multilayered Si Anodes with Embedded Nanoparticle Scaffolds for Li-Ion BatteriesAdvanced Science, 2017; 1700180 DOI: 10.1002/advs.201700180

DNA and Nanotechnology: Protein ‘Rebar’ could help make Error-Free Nanostructures: NIST


DNA proteinrebarThe protein RecA (purple units), wraps around and fortifies double-stranded DNA, enabling scientists to build large structures with the genetic material. Credit: NIST

DNA is the stuff of life, but it is also the stuff of nanotechnology. Because molecules of DNA with complementary chemical structures recognize and bind to one another, strands of DNA can fit together like Lego blocks to make nanoscale objects of complex shape and structure.

But researchers need to work with much larger assemblages of DNA to realize a key goal: building durable miniature devices such as biosensors and drug-delivery containers. That’s been difficult because long chains of DNA are floppy and the standard method of assembling long chains is prone to error.

Using a DNA-binding protein called RecA as a kind of nanoscale rebar, or reinforcing bar, to support the floppy DNA scaffolding, researchers at the National Institute of Standards and Technology (NIST) have constructed several of the largest rectangular, linear and other shapes ever assembled from DNA. The structures can be two to three times larger than those built using standard DNA self-assembly techniques.

In addition, because the new method requires fewer chemically distinct pieces to build organized structures than the standard technique, known as DNA origami, it is likely to reduce the number of errors in constructing the shapes. That’s a big plus for the effort to produce reliable DNA-based devices in large quantities, said NIST researcher Alex Liddle.

Although RecA’s ability to bind to double-stranded DNA has been known for years, the NIST team is the first to integrate filaments of this protein into the assembly of DNA structures. The addition of RecA offers a particular advantage: Once one unit of the protein binds to a small segment of double-stranded DNA, it automatically attracts other units to line up alongside it, in the same way that bar magnets will join end-to-end. Like bricks filling out a foundation, RecA lines the entire length of the DNA strand, stretching, widening and strengthening it. A floppy, 2-nanometer-wide strand of DNA can transform into a rigid structure more than four times as wide.

“The RecA method greatly extends the ability of DNA self-assembly methods to build larger and more sophisticated structures,” said NIST’s Daniel Schiffels.

Schiffels, Liddle and their colleague Veronika Szalai describe their work in a recent article in ACS Nano.

The new method incorporates the DNA origami technique and goes beyond it, according to Liddle. In DNA origami, short strands of DNA that have a specific sequence of four base pairs are used as staples to tie together long sections of DNA. To make the skinny DNA skeleton stronger and thicker, the strand may loop back on itself, quickly using up the long string.

If DNA origami is all about the folding, Liddle likened his team’s new method to building a room, starting with a floor plan. The location of the short, single-stranded pieces of DNA that act as staples mark the corners of the room. Between the corners lies a long, skinny piece of single-stranded DNA. The enzyme DNA polymerase transforms a section of the long piece of single-stranded DNA into the double-stranded version of the molecule, a necessary step because RecA only binds strongly to double-stranded DNA. Then RecA assembles all along the double strand, reinforcing the DNA  and limiting the need for extra staples to maintain its shape.

With fewer staples required, the RecA  is likely able to build organized structures with fewer errors than DNA origami, Liddle said.

 Explore further: The promise of nanomanufacturing using DNA origami

More information: Daniel Schiffels et al. Molecular Precision at Micrometer Length Scales: Hierarchical Assembly of DNA–Protein Nanostructures, ACS Nano (2017). DOI: 10.1021/acsnano.7b00320