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Nanomaterial inspired by nature paves way for greener energy (w/video)
Posted: Dec 21st, 2012
(Nanowerk News) A new nanomaterial, which finds its inspiration in nature, will provide the potential for more efficient and greener vehicles, rechargeable batteries and solar cells.
Researchers at the University of Reading have patented a new method of making electrode coatings with a thousand-fold increase in surface area compared with a flat electrode. This larger surface means that conversion of fuel or sunlight into electricity can take place in a smaller, more compact cell, making the cells cheaper to produce. The chemical reaction to create the energy also takes place at room temperature allowing the cells to be fitted to cheap materials such as plastic for the first time.
Based on structures found in the natural world which occur within mitochondria and chloroplasts, nature's own "fuel cells" and "solar cells", the new nanostructure is formed of a network of tiny wires, millionths of a millimetre in size, and is created by growing the metal in a template made from a plant molecule. This creates a structure known as a "bicontinuous cubic phase".
Dr Adam Squires, of the Department of Chemistry at the University of Reading, said: "Making electrodes more efficient lies at the heart of making our energy production more sustainable. This novel electrode coating technique has applications for fuel cells¹ in the newest generation of hybrid cars, photovoltaic cells, rechargeable batteries or battery production for a wide range of green technologies."
The process works in water using a technique known as electrochemical deposition, similar to silver plating a coin, and can be applied to any conducting electrode, creating a low cost, mass manufacture component. The unique 3D nanostructure enables much better conductivity and is the ideal shape for a high area electrode to create a more effective energy supply. Potentially, the technique could lead to energy storage devices with much greater capacity than traditional cells.
Dr Squires continued: "The method of production is chemically mild, environmentally friendly and crucially takes place at room temperature, which means that electrodes could be fitted to a range of other materials. It will allow, for example, photovoltaic cells to be located on a plastic base rather than the currently used metal or glass, which will make renewable energy technologies more flexible, lightweight and cost effective."
The work was carried out by Dr Samina Akbar when she was a PhD student at the University of Reading, in a joint project between the research groups of Dr Adam Squires and Dr Joanne Elliott. The findings are published in the journal Advanced Materials ("Facile Production of Ordered 3D Platinum Nanowire Networks with “Single Diamond” Bicontinuous Cubic Morphology") this week.
Source: University of Reading
http://www.nanowerk.com/news2/newsid=28207.php
Sponge-like graphene makes promising supercapacitor electrodes
October 12, 2012 by Lisa Zyga
SEM micrographs of the 3D sponge-like graphene, which can be used as electrodes in supercapacitors with ultrahigh power density and relatively good energy density. Image credit: Zhanwei Xu, et al. ©2012 American Chemical Society (Phys.org)
—While most of today's electric vehicles rely on batteries to store energy, supercapacitors have enjoyed significant improvements that have made them serious competitors to batteries. Batteries traditionally have the upper hand in terms of capacity, since supercapacitors' low capacities mean very short driving ranges for electric vehicles. Supercapacitors' biggest advantage lies in their much higher power density compared to batteries, enabling a quicker charge time and the ability to quickly discharge for fast acceleration.
A new study by a group of researchers at the University of Alberta and the National Research Council of Canada, both in Alberta, Canada, has shown that supercapacitors have great potential for continuing improvements.
The researchers have synthesized a new material that they call sponge-like graphene due to its 3D macroporous structure and demonstrated that it can be used to make supercapacitor electrodes. Supercapacitors with these new electrodes have fair energy density when operating at low power densities, but their biggest attraction is when operating at ultrahigh power densities of around 48,000 W/kg, where they're able to deliver an attractive energy density of 7.1 Wh/kg.
At first, an energy density of 7.1 Wh/kg may not sound remarkable compared to the energy density of the best Li-ion batteries, such as Envia System's record-breaking 400 Wh/kg announced earlier this year. However, in order to reduce the time it takes to charge Li-ion batteries for electric vehicles from hours to minutes, batteries need to have a higher power density than their current best values of around 10,000 W/kg. So the 48,000 W/kg power density of the supercapacitors reported here, coupled with a 7.1 Wh/kg energy density, shows that supercapacitors may offer batteries some competition.
"Supercapacitors and batteries are quite different electrochemical energy storage devices," coauthor Zhi Li, of both the University of Alberta and the National Research Council of Canada, told Phys.org. "Here is an example used quite often to demonstrate their differences. If you are driving an electric vehicle, you would like a high-energy-density battery to keep the vehicle running for many miles and you would probably also prefer a high-power-density supercapacitor to make the car start/accelerate faster. Supercapacitors are designed to work at much higher power density (fast charging/discharging). 7.1 Wh/kg is far from attractive for a battery. However, this energy is delivered in less than 2 seconds. I believe none of the existing batteries is ready to do that."
The synthesis process in which graphene is grown between CNTs, resulting in 3D sponge-like graphene. Image credit: Zhanwei Xu, et al. ©2012 American Chemical Society
http://phys.org/news/2012-10-sponge-like-graphene-supercapacitor-electrodes.html
http://dx.doi.org/10.1021/jz301207g
Batteries made from graphene could power tomorrow's electric cars
Posted: Aug 20th, 2012
(Nanowerk News) Engineering researchers at Rensselaer Polytechnic Institute made a sheet of paper from the world’s thinnest material, graphene, and then zapped the paper with a laser or camera flash to blemish it with countless cracks, pores, and other imperfections. The result is a graphene anode material that can be charged or discharged 10 times faster than conventional graphite anodes used in today’s lithium (Li)-ion batteries.
Rechargeable Li-ion batteries are the industry standard for mobile phones, laptop and tablet computers, electric cars, and a range of other devices. While Li-ion batteries have a high energy density and can store large amounts of energy, they suffer from a low power density and are unable to quickly accept or discharge energy. This low power density is why it takes about an hour to charge your mobile phone or laptop battery, and why electric automobile engines cannot rely on batteries alone and require a supercapacitor for high-power functions such as acceleration and braking.
The Rensselaer research team, led by nanomaterials expert Nikhil Koratkar, sought to solve this problem and create a new battery that could hold large amounts of energy but also quickly accept and release this energy. Such an innovation could alleviate the need for the complex pairing of Li-ion batteries and supercapacitors in electric cars, and lead to simpler, better-performing automotive engines based solely on high-energy, high-power Li-ion batteries. Koratkar and his team are confident their new battery, created by intentionally engineering defects in graphene, is a critical stepping stone on the path to realizing this grand goal. Such batteries could also significantly shorten the time it takes to charge portable electronic devices from phones and laptops to medical devices used by paramedics and first responders.
SEM image of the cross section of photo-thermally reduced graphene shows an expanded structure. The graphene sheets are spaced apart with an inter-connected network allowing for greater electrolyte wetting and lithium ion access for efficient high rate performance in lithium ions batteries.
http://pubs.acs.org/doi/abs/10.1021/nn303145j
“Li-ion battery technology is magnificent, but truly hampered by its limited power density and its inability to quickly accept or discharge large amounts of energy. By using our defect-engineered graphene paper in the battery architecture, I think we can help overcome this limitation,” said Koratkar, the John A. Clark and Edward T. Crossan Professor of Engineering at Rensselaer. “We believe this discovery is ripe for commercialization, and can make a significant impact on the development of new batteries and electrical systems for electric automobiles and portable electronics applications.”
Results of the study were published this week by the journal ACS Nano ("Photothermally Reduced Graphene as High-Power Anodes for Lithium-Ion Batteries").
http://dx.doi.org/doi:10.1021/nn303145j
Koratkar and his team started investigating graphene as a possible replacement for the graphite used as the anode material in today’s Li-ion batteries. Essentially a single layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence. In previous studies, Li-ion batteries with graphite anodes exhibited good energy density but low power density, meaning they could not charge or discharge quickly. This slow charging and discharging was because lithium ions could only physically enter or exit the battery’s graphite anode from the edges, and slowly work their way across the length of the individual layers of graphene.
Koratkar’s solution was to use a known technique to create a large sheet of graphene oxide paper. This paper is about the thickness of a piece of everyday printer paper, and can be made nearly any size or shape. The research team then exposed some of the graphene oxide paper to a laser, and other samples of the paper were exposed to a simple flash from a digital camera. In both instances, the heat from the laser or photoflash literally caused mini-explosions throughout the paper, as the oxygen atoms in graphene oxide were violently expelled from the structure. The aftermath of this oxygen exodus was sheets of graphene pockmarked with countless cracks, pores, voids, and other blemishes. The pressure created by the escaping oxygen also prompted the graphene paper to expand five-fold in thickness, creating large voids between the individual graphene sheets.
The researchers quickly learned this damaged graphene paper performed remarkably well as an anode for a Li-ion battery.
Whereas before the lithium ions slowly traversed the full length of graphene sheets to charge or discharge, the ions now used the cracks and pores as shortcuts to move quickly into or out of the graphene—greatly increasing the battery’s overall power density.
Koratkar’s team demonstrated how their experimental anode material could charge or discharge 10 times faster than conventional anodes in Li-ion batteries without incurring a significant loss in its energy density. Despite the countless microscale pores, cracks, and voids that are ubiquitous throughout the structure, the graphene paper anode is remarkably robust, and continued to perform successfully even after more than 1,000 charge/discharge cycles. The high electrical conductivity of the graphene sheets also enabled efficient electron transport in the anode, which is another necessary property for high-power applications.
Koratkar said the process of making these new graphene paper anodes for Li-ion batteries can easily be scaled up to suit the needs of industry. The graphene paper can be made in essentially any size and shape, and the photo-thermal exposure by laser or camera flashes is an easy and inexpensive process to replicate.
The researchers have filed for patent protection for their discovery. The next step for this research project is to pair the graphene anode material with a high-power cathode material to construct a full battery.
Source: Case Western Reserve University
http://www.nanowerk.com/news2/newsid=26421.php
Towards artificial photosynthesis for solar hydrogen generation
Posted: Dec 19th, 2011
(Nanowerk News) Photosynthesis is considered the "Holy Grail" in the field of sustainable energy generation because it directly converts solar energy into storable fuel using nothing but water and carbon dioxide (CO2). Scientists have long tried to mimic the underlying natural processes and to optimize them for energy device applications such as photo-electrochemical cells (PEC), which use sunlight to electrochemically split water – and thus directly generate hydrogen, cutting short the more conventional approach using photovoltaic cells for the electrolysis of water.
Traditionally, PEC electrodes are made of semiconducting materials such as metal oxides, some of which are also known for their photocatalytic properties. For quite some time, researchers at Empa's Laboratory for High Performance Ceramics (LHPC) have been investigating nanoparticles of these materials, for instance titanium dioxide (TiO2), for the neutralization of organic pollutants in air and water. Collaborating with colleagues at the University of Basel and at Argonne National Laboratory in the US, they now succeeded in making a nano-bio PEC electrode, consisting of iron oxide conjugated with a protein from blue-green algae (also known as cyanobacteria), which is twice as efficient in water splitting as iron oxide alone (see paper in Advanced Functional Materials: ("Functionalization of Nanostructured Hematite Thin-Film Electrodes with the Light-Harvesting Membrane Protein C-Phycocyanin Yields an Enhanced Photocurrent").
http://dx.doi.org/doi:10.1002/adfm.201101830
Hematite nanoparticle film (red) with functional phycocyanin network (green) attached. (Image by Dr. E. Vitol, Argonne National Laboratory)
Inspired by photosynthesis
Iron oxide, in particular hematite (a-Fe2O3), is a promising electrode material for PEC because it is susceptible to visible wavelengths and thus uses sunlight more efficiently than photocatalysts like TiO2, which can only use the UV part of solar radiation. What's more, hematite is a low-cost and abundant material.
The second ingredient in the novel electrode "recipe" is phycocyanin, a protein from blue-green algae. "I was inspired by the natural photosynthetic machinery of cyanobacteria where phycocyanin acts as a major light-harvesting component. I wanted to make artificial photosynthesis using ceramics and proteins", recalls Debajeet K. Bora who designed the new electrode during his PhD thesis at Empa. "The concept of hematite surface functionalization with proteins was completely novel in PEC research."
After Bora covalently cross-coupled phycocyanin to hematite nanoparticles that had been immobilized as a thin film, the conjugated hematite absorbed many more photons than without the algal protein. In fact, the induced photocurrent of the hybrid electrode was doubled compared to a "normal" iron oxide electrode.
One tough cookie
Somewhat surprisingly, the light harvesting protein complex does not get destroyed while in contact with a photocatalyst in an alkaline environment under strong illumination. Chemists would have predicted the complete denaturation of biomolecules under such corrosive and aggressive conditions. "Photocatalysts are designed to destroy organic pollutants, which are a burden to the environment. But here we have a different situation", says Artur Braun, group leader at Empa's LHPC and principal investigator of the study. "There seems to be a delicate balance where organic molecules not only survive harsh photocatalytic conditions, but even convey an additional benefit to ceramic photocatalysts: They double the photocurrent. This is a big step forward".
The project was fully funded by the Swiss Federal Office of Energy (SFOE). Bora who will soon have completed his PhD thesis says he will continue what he started at Empa during a postdoc at the University of California, Berkeley, which he will assume early next year.
Source: Empa
http://www.nanowerk.com/news/newsid=23783.php
Carbon nanotube-coated sponge makes an excellent supercapacitor
Posted: December 6, 2011
(Nanowerk Spotlight) Ultra- or supercapacitors are emerging as a key enabling storage technology for use in fuel-efficient transport as well as in renewable energy (for instance as power grid buffer). These devices combine the advantages of conventional capacitors – they can rapidly deliver high current densities on demand – and batteries – they can store a large amount of electrical energy.
Supercapacitors offer a low-cost alternative source of energy to replace rechargeable batteries for various applications, such as power tools, mobile electronics, and electric vehicles. A number of auto makers are exploring the concept of combining supercapacitors with Li-ion batteries as a next generation energy storage system for their electric hybrid vehicles. Although the energy density of capacitors is quite low compared to batteries, their power density is much higher, allowing them to provide bursts of electric energy that can help the new generation of cars to accelerate at comparable or better rates than traditional petrol-only engine vehicles, while achieving a significantly reduced fuel consumption (read more about supercapacitors and other nanotechnologies to mitigate global warming).
Researchers have now fabricated novel high-performance sponge supercapacitors using a simple and scalable method. Reporting their work in a recent edition of Nano Letters ("High-Performance Nanostructured Supercapacitors on a Sponge"), a team at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, led by Husam N. Alshareef, shows that three-dimensional electrodes potentially have a huge advantage over conventional mixed electrode materials.
http://dx.doi.org/doi:10.1021/nl2023433
"We showed supercapacitor electrodes fabricated on a macroporous structure give a boost to the speed and specific capacitance of the supercapacitors," Alshareef tells Nanowerk. "We worked with sponges because they offer novel exciting characteristics different from paper and textile: first, sponge has much more uniform size of macropores. Second, the cellulose or polyester fibers are interconnected virtually free of junctions. Therefore, continuous coating of conducting nanomaterials is much easier since there are no junctions to cross."
Characterizations of MnO2-CNT-sponge electrodes: (a) an overall view of 3D macroporous hierarchical MnO2-CNT-sponge electrode; (b) MnO2 uniformly deposited on the skeleton of CNT-sponge; (c) high magnification of porous MnO2 nanoparticles on CNT-sponge, inset shows morphology of an individual MnO2 flower-like particle. (Reprinted with permission from American Chemical Society)
The sponge-based supercapacitors were designed and fabricated by the KAUST team using a simple and scalable method. Their fabrication process consisted of four simple steps: First, a piece of commercially available sponge was cleaned by water and acetone; then, after drying, it was cut into small ribbons; these ribbons were coated with a carbon nanotube (CNT) ink; and finally, the researchers electrodeposited manganese dioxide (MnO2) nanoparticles onto the CNT-coated sponge.
"Due to the mechanical flexibility of carbon nanotubes and strong van der Waals interactions between the macroporous sponge cellulose and carbon nanotubes, the nanotubes can be easily coated onto the skeleton of a sponge, rendering the insulating sponge highly conductive by a simple dipping and drying process" explains Alshareef.
Examining the CNT-coated sponge, the researchers found that it still maintained a hierarchical macroporous nature where its intricate assembly of pores remained open to allow the flow of electrolyte. The carbon nanotubes formed a thin layer wrapped around the skeleton of the sponge.
"We also tested the mechanical resilience of the CNT-sponge skeleton by folding, twisting, and stretching it repeatedly," says Alshareef. "After all the mechanical tests, the sponge always reverted to its original shape without any permanent deformation."
The team also tested the electrochemical performance of their sponge supercapacitors. "The macroporous nature of the sponge along with the porous nature of the electrodeposited MnO2 nanoparticles provided a double porous electrode structure giving good conductivity and full accessibility of electrolyte to MnO2, improving the performances of MnO2-CNT-sponge supercapacitors dramatically," says Alshareef. "We found that our sponge supercapacitor exhibits high specific capacitance, ultrafast charge-discharge rate, excellent cycling stability, and good energy and power density, making it a promising electrode for future energy storage systems."
In what could be an interesting aspect for small mobile electronic appliances, the finished supercapacitor sponge turns out to be much lighter than a rigid metal or other flexible substrates with the same area: a sponge with an area of 2 square centimeters and a thickness of 1 millimeter weighs only about 10 mg.
By Michael Berger. Copyright © Nanowerk
http://www.nanowerk.com/spotlight/spotid=23649.php
Shuttle fluoride increases storage capacity
Press Release 151/2011
[GOOGLE TRANSLATION]
KIT scientists are developing a new concept for rechargeable batteries
Structure of the fluoride-ion battery: a fluoride electrolyte separates the anode from the cathode metal and metal fluoride. (Photo: KIT)
A new concept for rechargeable batteries, researchers have developed the kit. Based on a fluoride-shuttle - the transfer of fluoride anions between the electrodes - it promises to be a multiple of the memory as it is possible for lithium-ion batteries. Even the reliability can be increased by reducing the need for lithium. In the "Journal of Materials Chemistry" are Dr. Maximilian Fichtner and Dr. Anji Reddy Munnangi the fluoride-ion battery before the first time.[ http://pubs.rsc.org/en/Content/ArticleLanding/2011/JM/c1jm13535j ]
Lithium-ion batteries are widely available - but their capacity is limited. In the future, be in demand with higher energy density, especially for mobile applications, battery systems, which can save more energy with less weight. KIT scientists conduct research, therefore, to alternative systems. A totally new concept for secondary batteries based on metal fluorides have developed Dr. Maximilian Fichtner, head of energy storage systems, and Dr. Anji Reddy Munnangi at the Institute of Nanotechnology (INT) of the KIT.
Metal fluorides can be used both as a conversion materials in lithium-ion batteries. They also allow lithium batteries with fluoride-free electrolyte, anode and cathode made of metal, metal fluoride, which have significantly higher storage capacity and enhanced security features. It takes the fluoride anion in place of lithium-cation the charge transfer. At anode and cathode, it is each to form a metal fluoride, or to its reduction. "There can be several electrons transferred per metal atom, this concept allows extremely high energy densities - up to ten times as high as with current lithium-ion batteries," explained Dr. Maximilian Fichtner.
The KIT researchers are now working to develop battery materials design and architecture to the initial capacity and to improve the cycle stability of the fluoride-ion battery. Another challenge is the development of electrolyte: The solid electrolyte used until now is only suitable for applications at elevated temperatures. The aim is therefore to find a suitable electrolyte for application liquid at room temperature.
M. Anji Reddy and M. Fichtner: Batteries based on fluoride shuttle. Journal of Materials Chemistry. 2011, Advance Article. DOI: 10.1039/C1JM13535J.
The Karlsruhe Institute of Technology (KIT) is a public corporation under the laws of the State of Baden-Wuerttemberg. It fulfills the mission of a university and the mission of a national research center of the Helmholtz Association. The KIT focuses on the knowledge triangle of research - teaching - innovation.
or, 19.10.2011
http://www.kit.edu/besuchen/pi_2011_8281.php
http://www.nanowerk.com/news/newsid=23143.php
Researchers dramatically increase the energy density of graphene-based supercapacitors
Posted: Sep 21st, 2011
(Nanowerk News) Professor Jie Tang, Group Leader of the 1D Nanomaterials Research Group of the Materials Processing Unit, National Institute for Materials Science, and Mr. Qian Cheng, a doctoral student and NIMS Junior Researcher in the same Group, have succeeded in dramatically increasing the energy density of supercapacitors, which are used to store electrical energy. This was realized by developing a new electrode in which graphene nanosheets are stacked in a layered structure with carbon nanotubes sandwiched between the graphene layers. This research achievement is published in the latest issue of Physical Chemistry Chemical Physics.
( http://pubs.rsc.org/en/content/articlelanding/2011/cp/c1cp21910c )
Various new batteries, such as nickel metal hydride batteries, are currently being developed with the aims of achieving higher efficiency and higher energy storage for electric power supplies. In comparison with batteries, capacitors have a larger output power density to enable rapid charging, excellent durability to allow operations in both higher and lower extreme temperatures, better cyclicity for recharging repeatedly over a long period, and are also safer. However, it has been as a great technical challenge to realize high energy density due to the relatively low specific capacity of the conventional capacitor devices.
In order to achieve a revolutionary increase in density of energy storage, Professor Tang and her team, in collaboration with Professor Lu-Chang Qin of the University of North Carolina at Chapel Hill in the United States, have designed and developed a graphene-based composite structure, in which graphene is used as the base material of the capacitor electrodes and carbon nanotubes (CNT) are inserted between the graphene sheets. In this structure graphene offers a far larger specific surface area (2630 m2/g) than the conventional materials and the CNTs function as spacers as well as conducting paths to enable adsorption of a larger quantity of electrolyte ions on the graphene surface. With this graphene-CNT composite as the capacitor electrodes, Professor Tang has obtained a high energy density of 62.8 Wh/kg and output power density of 58.5 kW/kg using organic electrolyte. By using an ionic liquid as the electrolyte, they have achieved an energy density of 155.6 Wh/kg, which is comparable to that of nickel metal hydride batteries.
Among the many industrial applications of capacitors, the new capacitors developed in this research offer promises as power sources for electric and hybrid vehicles, which require high energy density. As the current production processes are also inexpensive and can be scaled up, large expectations are placed on practical applications.
Source: NIMS
http://www.nanowerk.com/news/newsid=22807.php
Breakthrough in hydrogen fuel cells: Chemists develop way to safely store, extract hydrogen
August 30, 2011
A team of USC scientists has developed a robust, efficient method of using hydrogen as a fuel source.
Hydrogen makes a great fuel because of it can easily be converted to electricity in a fuel cell and because it is carbon free. The downside of hydrogen is that, because it is a gas, it can only be stored in high pressure or cryogenic tanks.
In a vehicle with a tank full of hydrogen, "if you got into a wreck, you'd have a problem," said Travis Williams, assistant professor of chemistry at the USC Dornsife College.
A possible solution is to store hydrogen in a safe chemical form. Earlier this year, Williams and his team figured out a way to release hydrogen from an innocuous chemical material — a nitrogen-boron complex, ammonia borane — that can be stored as a stable solid.
Now the team has developed a catalyst system that releases enough hydrogen from its storage in ammonia borane to make it usable as a fuel source. Moreover, the system is air-stable and re-usable, unlike other systems for hydrogen storage on boron and metal hydrides.
The research was published this month in the Journal of the American Chemical Society.
"Ours is the first game in town for reusable, air stabile ammonia borane dehydrogenation," Williams said, adding that the USC Stevens Institute is in the process of patenting the system.
The system is sufficiently lightweight and efficient to have potential fuel applications ranging from motor-driven cycles to small aircraft, he said.
More information: A Robust, Air-Stable, Reusable Ruthenium Catalyst for Dehydrogenation of Ammonia Borane, J. Am. Chem. Soc., Article ASAP.
DOI: 10.1021/ja2058154
http://dx.doi.org/10.1021/ja2058154
Abstract
We describe an efficient homogeneous ruthenium catalyst for the dehydrogenation of ammonia borane (AB). This catalyst liberates more than 2 equiv of H2 and up to 4.6 system wt % H2 from concentrated AB suspensions under air. Importantly, this catalyst is robust, delivering several cycles of dehydrogenation at high [AB] without loss of catalytic activity, even with exposure to air and water.
Provided by University of Southern California
http://www.physorg.com/news/2011-08-breakthrough-hydrogen-fuel-cells-chemists.html
A microporous polymer is an unusually powerful supercapacitor
Posted: Aug 22nd, 2011
(Nanowerk News) For future electric vehicles, powerful notebook computers, and other portable devices, we need a new generation of energy storage materials that are better suited to modern needs than current rechargeable batteries. The best materials for this are known as supercapacitors. A team led by Dinglin Jiang at the National Institutes of Natural Sciences in Okazaki (Japan) has now introduced a new material with outstanding supercapacitor properties in the journal Angewandte Chemie ("Supercapacitive Energy Storage and Electric Power Supply Using an Aza-Fused p-Conjugated Microporous Framework") http://onlinelibrary.wiley.com/doi/10.1002/anie.201103493/abstract;jsessionid=7C17789C27B6042C836FEE7B56F8A365.d03t03 .
A p-conjugated microporous polymer with aza-fused framework is reported. The porous framework is conductive and allows electrolyte ions to move into the pores because of structural features.
Emission-free electric cars are well suited for drives around the city; for long stretches, however, this has not been the case. The problem stems from the small amount of energy that can be stored, which covers only short distances before requiring a charge, and the amount of current that can be delivered, which limits the speed and acceleration of the vehicles. Supercapacitors could overcome these challenges because they combine the advantages of earlier capacitors and batteries: like a capacitor, they can deliver high current densities on demand while storing a large amount of electric energy like a battery.
Supercapacitors work on a different charge-storage principle than rechargeable batteries, and consist of electrochemical double layers on electrodes, which are wetted by an electrolyte. When a voltage is applied, ions of opposite charge collect on both electrodes to form wafer-thin zones of immobilized charge carriers. In contrast to a battery, there is only a shift of charge; no chemical transformation occurs. Various materials are suitable for supercapacitors, but the truly perfect material has yet to be found. The researchers in Japan have now reached an important milestone along the way.
There is one class of materials with interesting properties: special microporous, framework-like, organic polymers. Their double bonds are arranged in such a way that some of their electrons can move freely over extended regions of the framework as an "electron cloud". Such materials are thus conducting. A large inner surface area is important for the formation of electrostatic charge-separation layers in the pores. Jiang and his team have now synthesized a nitrogen-containing framework with a pore size optimal for allowing ions to flow in and out rapidly – a requirement for rapid charging and discharging. The nitrogen centers interact with the electrolyte ions, thus favoring the accumulation of charge and the movement of ions.
The interplay between these different advantageous properties provides the new material with an unusually high charge storage capacity and high energy density. Jiang and his co-workers were able to demonstrate that their microporous frameworks can withstand many charge/discharge cycles.
Source: Wiley-VCH Verlag
http://www.nanowerk.com/news/newsid=22487.php
New energy storage device could recharge electric vehicles in minutes
August 19, 2011 by Lisa Zyga
Compared with supercapacitors and batteries, SMCs (with three different electrode thicknesses shown) offer both a high power density and high energy density. Image copyright: Jang, et al. ©2011 American Chemical Society
(PhysOrg.com) -- It has all the appearances of a breakthrough in battery technology, except that it’s not a battery. Researchers at Nanotek Instruments, Inc., and its subsidiary Angstron Materials, Inc., in Dayton, Ohio, have developed a new paradigm for designing energy storage devices that is based on rapidly shuttling large numbers of lithium ions between electrodes with massive graphene surfaces. The energy storage device could prove extremely useful for electric vehicles, where it could reduce the recharge time from hours to less than a minute. Other applications could include renewable energy storage (for example, storing solar and wind energy) and smart grids.
The researchers call the new devices "graphene surface-enabled lithium ion-exchanging cells," or more simply, "surface-mediated cells" (SMCs). Although the devices currently use unoptimized materials and configurations, they can already outperform Li-ion batteries and supercapacitors. The new devices can deliver a power density of 100 kW/kgcell, which is 100 times higher than that of commercial Li-ion batteries and 10 times higher than that of supercapacitors. The higher the power density, the faster the rate of energy transfer (resulting in a faster recharge time). In addition, the new cells can store an energy density of 160 Wh/kgcell, which is comparable to commercial Li-ion batteries and 30 times higher than that of conventional supercapacitors. The greater the energy density, the more energy the device can store for the same volume (resulting in a longer driving range for electric vehicles).
“Given the same device weight, the current SMC and Li-ion battery can provide an electric vehicle (EV) with a comparable driving range,” Bor Z. Jang, co-founder of Nanotek Instruments and Angstron Materials, told PhysOrg.com. “Our SMCs, just like the current Li-ion batteries, can be further improved in terms of energy density [and therefore range]. However, in principle, the SMC can be recharged in minutes (possibly less than one minute), as opposed to hours for Li-ion batteries used in current EVs.”
Jang and his coauthors at Nanotek Instruments and Angstron Materials have published the study on the next-generation energy storage devices in a recent issue of Nano Letters. Both companies specialize in nanomaterial commercialization, with Angstron being the world’s largest producer of nano graphene platelets (NGPs).
As the researchers explain in their study, batteries and supercapacitors each have their respective strengths and weaknesses when it comes to energy storage. While Li-ion batteries provide a much higher energy density (120-150 Wh/kgcell) than supercapacitors (5 Wh/kgcell), the batteries deliver a much lower power density (1 kW/kgcell compared to 10 kW/kgcell). Many research groups have made efforts to increase the power density of Li-ion batteries and increase the energy density of supercapacitors, but both areas still have significant challenges. By providing a fundamentally new framework for energy storage devices, the SMCs could enable researchers to bypass these challenges.
“The development of this new class of energy storage devices bridges the performance gap between a Li-ion battery and a supercapacitor,” Jang said. “More significantly, this fundamentally new framework for constructing energy storage devices could enable researchers to achieve both the high energy density and high power density without having to sacrifice one to achieve the other.”
The large surface areas of the SMCs’ electrodes enable rapid shuttling of large numbers of ions between electrodes, resulting in a fast recharge time. Image copyright: Jang, et al. ©2011 American Chemical Society
The key to the SMCs’ performance is a cathode and anode that contain very large graphene surfaces. When fabricating the cell, the researchers put lithium metal (in the form of particles or foil) at the anode. During the first discharge cycle, the lithium is ionized, resulting in a much larger number of lithium ions than in Li-ion batteries. As the battery is used, the ions migrate through a liquid electrolyte to the cathode, where the ions enter the pores and reach the large graphene surface inside the cathode. During recharging, a massive flux of lithium ions quickly migrates from the cathode to the anode. The electrodes’ large surface areas enable the rapid shuttling of large numbers of ions between electrodes, resulting in their high power and energy densities.
As the researchers explain, the exchange of lithium ions between the porous electrodes’ surfaces (and not in the bulk of the electrode, as in batteries) completely removes the need for the time-consuming process of intercalation. In this process, the lithium ions must be inserted inside the electrodes, which dominates the charging time of batteries.
Although in this study the researchers prepared different types of graphene (oxidized, and reduced single-layer and multilayer) from a variety of different types of graphite, further analysis of the materials and configuration is needed for optimizing the device. For one thing, the researchers plan to further investigate the cells’ cycling lifetime. So far, they found that the devices could retain 95% capacity after 1,000 cycles, and even after 2,000 cycles showed no evidence of dendrite formation.
The researchers also plan to investigate the relative roles of different lithium storage mechanisms on the device’s performance.
“We do not anticipate any major hurdle to commercialization of the SMC technology,” Jang said. “Although graphene is currently sold at a premium price, Angstron Materials, Inc., is actively engaged in scaling up the production capacity of graphene. The production costs of graphene are expected to be dramatically reduced within the next 1-3 years.”
More information: Bor Z. Jang, et al. “Graphene Surface-Enabled Lithium-Ion Exchanging Cells: Next-Generation High-Power Energy Storage Devices.” Nano Letters. DOI:10.1021/nl2018492
http://dx.doi.org/10.1021/nl2018492
http://www.physorg.com/news/2011-08-energy-storage-device-recharge-electric.html
Hybrid Solar System Makes Rooftop Hydrogen
This is the hybrid system schematic. (Credit: Nico Hotz)
ScienceDaily (Aug. 9, 2011) — While roofs across the world sport photovoltaic solar panels to convert sunlight into electricity, a Duke University engineer believes a novel hybrid system can wring even more useful energy out of the sun's rays.
Instead of systems based on standard solar panels, Duke engineer Nico Hotz proposes a hybrid option in which sunlight heats a combination of water and methanol in a maze of glass tubes on a rooftop. After two catalytic reactions, the system produces hydrogen much more efficiently than current technology without significant impurities. The resulting hydrogen can be stored and used on demand in fuel cells.
For his analysis, Hotz compared the hybrid system to three different technologies in terms of their exergetic performance. Exergy is a way of describing how much of a given quantity of energy can theoretically be converted to useful work.
"The hybrid system achieved exergetic efficiencies of 28.5 percent in the summer and 18.5 percent in the winter, compared to 5 to 15 percent for the conventional systems in the summer, and 2.5 to 5 percent in the winter," said Hotz, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering.
The paper describing the results of Hotz's analysis was named the top paper during the ASME Energy Sustainability Fuel Cell 2011 conference in Washington, D.C. Hotz recently joined the Duke faculty after completing post-graduate work at the University of California-Berkeley, where he analyzed a model of the new system. He is currently constructing one of the systems at Duke to test whether or not the theoretical efficiencies are born out experimentally.
Hotz's comparisons took place during the months of July and February in order to measure each system's performance during summer and winter months.
Like other solar-based systems, the hybrid system begins with the collection of sunlight. Then things get different. While the hybrid device might look like a traditional solar collector from the distance, it is actually a series of copper tubes coated with a thin layer of aluminum and aluminum oxide and partly filled with catalytic nanoparticles. A combination of water and methanol flows through the tubes, which are sealed in a vacuum.
"This set-up allows up to 95 percent of the sunlight to be absorbed with very little being lost as heat to the surroundings," Hotz said. "This is crucial because it permits us to achieve temperatures of well over 200 degrees Celsius within the tubes. By comparison, a standard solar collector can only heat water between 60 and 70 degrees Celsius."
Once the evaporated liquid achieves these higher temperatures, tiny amounts of a catalyst are added, which produces hydrogen. This combination of high temperature and added catalysts produces hydrogen very efficiently, Hotz said. The resulting hydrogen can then be immediately directed to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later.
The three systems examined in the analysis were the standard photovoltaic cell which converts sunlight directly into electricity to then split water electrolytically into hydrogen and oxygen; a photocatalytic system producing hydrogen similar to Hotz's system, but simpler and not mature yet; and a system in which photovoltaic cells turn sunlight into electricity which is then stored in different types of batteries (with lithium ion being the most efficient).
"We performed a cost analysis and found that the hybrid solar-methanol is the least expensive solution, considering the total installation costs of $7,900 if designed to fulfill the requirements in summer, although this is still much more expensive than a conventional fossil fuel-fed generator," Hotz said.
Costs and efficiencies of systems can vary widely depending on location -- since the roof-mounted collectors that could provide all the building's needs in summer might not be enough for winter. A rooftop system large enough to supply all of a winter's electrical needs would produce more energy than needed in summer, so the owner could decide to shut down portions of the rooftop structure or, if possible, sell excess energy back to the grid.
"The installation costs per year including the fuel costs, and the price per amount of electricity produced, however showed that the (hybrid) solar scenarios can compete with the fossil fuel-based system to some degree," Hotz said. 'In summer, the first and third scenarios, as well as the hybrid system, are cheaper than a propane- or diesel-combusting generator."
This could be an important consideration, especially if a structure is to be located in a remote area where traditional forms of energy would be too difficult or expensive to obtain.
Hotz's research was supported by the Swiss National Science Fund. Joining him in the study were UC-Berkeley's Heng Pan and Costas Grigoropoulos, as well as Seung H. Ko of the Korea Advanced Institute of Science and Technology, Daejon.
http://www.sciencedaily.com/releases/2011/08/110809132232.htm
See also EP 2143490:
http://worldwide.espacenet.com/publicationDetails/biblio?FT=D&date=20100113&DB=EPODOC&locale=en_EP&CC=EP&NR=2143490A1&KC=A1
Power pillars: This battery electrode, shown in cross section under an electron microscope, consists of nanoscale tin pillars sandwiched between sheets of graphene.
Credit: Lawrence Berkeley
Nanoscale Pillars Could Have a Big Role in Future Batteries
A new fabrication technique lets batteries use tin electrodes, and store more energy.
TUESDAY, AUGUST 2, 2011
BY KATHERINE BOURZAC
Tin, silicon, and a few other elements have long been languishing on chemists' list of electrode materials that could, in theory, help lithium-ion batteries hold more energy. A new way of structuring these materials could at last allow them to be used in this way.
Researchers at the Lawrence Berkeley National Laboratory made tin electrodes by using layers of graphene to protect the normally fragile tin. These first tin electrodes are a sign that materials scientists have made a great deal of progress in using nanoscale structures to improve batteries.
Making battery electrodes from tin or silicon can boost the battery's overall energy storage. That's because such materials can take in more lithium during charging and recharging than carbon, which is normally used. But silicon and tin tend to be unstable as electrodes. Tin takes up so much lithium that it expands in volume by a factor of two to three during charging. "This forms cracks, and the tin leaks into the electrolyte and is lost," says Yuegang Zhang, a scientist at Lawrence Berkeley.
Zhang's clever solution is to layer the tin between sheets of graphene, single-atom-thick sheets of carbon mesh. Graphene is highly conductive, and while it's flexible, it's also the strongest material ever tested.
The tin-graphene electrode consists of two layers of tin nanopillars sandwiched between three sheets of graphene. The pillars help the electrode remain stable: instead of fracturing, the tin expands and contracts during charging without breaking. The space between the pillars means there's plenty of room for the battery's electrolyte to move around, which ensures fast charging speeds.
Zhang's group has made prototype batteries featuring these electrodes. The prototype tin-graphene batteries can charge up in about 10 minutes and store about 700 milliamp-hours per gram of charge. This storage capacity is maintained over 30 charge cycles. The batteries will ultimately need to hold their performance for hundreds of charge cycles. "The performance they have is quite reasonable, and this has a pretty clear application in existing batteries," says Yi Cui, associate professor of materials science at Stanford University. Cui was not involved with the work.
Several other research groups are working on promising battery materials that include nanoscale structures. Cui has founded a company called Amprius to commercialize another kind of battery anode that features silicon nanowires. The nanostructure of these wires also helps the fragile material remain stable as it takes up and releases lithium. Another group, led by Pulickel Ajayan at Rice, recently built a nanostructured battery that incorporates a tin electrode, in this case integrating the electrodes and the electrolyte on individual nanowires. Arrayed together, these nanowires could make long-lasting microbatteries for small devices such as sensors.
Zhang is working to demonstrate the use of the nanopillar structure with other fragile electrode materials, including silicon. The process may add to the cost of battery production, but the performance gains could offset the potential additional cost. "People typically assume that a fancy nanoscale structure will cost more, but it may not," says Zhang.
http://www.technologyreview.com/energy/38205/?nlid=nldly&nld=2011-08-03
Graphite + water = the future of energy storage
Posted: Jul 15th, 2011
(Nanowerk News) A combination of two ordinary materials – graphite and water – could produce energy storage systems that perform on par with lithium ion batteries, but recharge in a matter of seconds and have an almost indefinite lifespan.
Dr Dan Li [ http://www.monash.edu.au/news/search?q=%22Dan%20Li%22 ], of the Monash University Department of Materials Engineering, and his research team have been working with a material called graphene, which could form the basis of the next generation of ultrafast energy storage systems.
"Once we can properly manipulate this material, your iPhone, for example, could charge in a few seconds, or possibly faster." said Dr Li.
Graphene is the result of breaking down graphite, a cheap, readily available material commonly used in pencils, into layers one atom thick. In this form, it has remarkable properties.
Graphene sheets.
Graphene is strong, chemically stable, an excellent conductor of electricity and, importantly, has an extremely high surface area.
Dr Li said these qualities make graphene highly suitable for energy storage applications.
"The reason graphene isn't being used everywhere is that these very thin sheets, when stacked into a usable macrostructure, immediately bond together, reforming graphite. When graphene restacks, most of the surface area is lost and it doesn't behave like graphene anymore."
Now, Dr Li and his team have discovered the key to maintaining the remarkable properties of separate graphene sheets: water. Keeping graphene moist – in gel form – provides repulsive forces between the sheets and prevents re-stacking, making it ready for real-world application.
"The technique is very simple and can easily be scaled up. When we discovered it, we thought it was unbelievable. We're taking two basic, inexpensive materials – water and graphite – and making this new nanomaterial with amazing properties," said Dr Li.
When used in energy devices, graphene gel significantly outperforms current carbon-based technology, both in terms of the amount of charge stored and how fast the charges can be delivered.
Dr Li said the benefits of developing this new nanotechnology extend beyond consumer electronics.
"High-speed, reliable and cost-effective energy storage systems are critical for the future viability of electricity from renewable resources. These systems are also the key to large-scale adoption of electrical vehicles.
"Graphene gel is also showing promise for use in water purification membranes, biomedical devices and sensors."
Dr Li has been working with graphene since 2006 and his team's research findings have recently been published in a number of prestigious journals including Advanced Materials, Angewandte Chemie and Chemical Communications.
Source: Monash University
http://www.nanowerk.com/news/newsid=22128.php
At the heart of the Cougar™ Platform is the Innovalight™ Silicon Ink. The proprietary material is comprised of silicon nano-particles dispersed in an environmentally friendly blend of chemicals. The result of over 100 engineering-years of ink development, Innovalight has optimized silicon particle size and dopant concentration to maximize the conversion efficiency of the Cougar Platform. Additionally, the material was formulated to be compatible with low-cost industry standard screen printers – the same tool cell manufacturers use for printing metal contacts.
To meet the demand of the Cougar Platform, Innovalight is ramping Silicon Ink production to support over 2,000 MW of Cougar Cells by June 2011.
http://innovalight.com/technology_solarink.htm
Energy production and storage developments using nanotechnology.
