Nanotechnology Brings First “Water – in – Salt” Batteries

The latest in nanotechnology has brought the world the first ‘water-in-salt” battery, which fuses water, salt and Lithium to make batteries as potent as regular Lithium-ion batteries. The team, from the U.S. Army Research Laboratory and the University of Maryland, have devised an energy source that does not come with the fire or chemical hazard that comes in regular Lithium-ion batteries.

Nanotechnology Makes Us Greener

The full report is published in the journal Science, and it constitutes a major breakthrough in aqueous Lithium-ion battery technology and nanotechnology. This ‘salt-in-water’ battery is twice as potent as any other aqueous battery developed, and has the longevity of the traditional Lithium-ion battery

According to the team, their nanotechnology research can be applied to large scale proportions, like electric vehicle technology or energy harvest systems and medical devices such as pacemakers or other electrical powered valves. Their research shows that aqueous batteries have the ability to power up to 2.3 Volts, meaning that they could replace regular Lithium-ion. We already use this technology in the digital world, but it could be blown up to much larger proportions.

This Breakthrough is the Product of Solid Electrolyte Interphase

The researchers achieved this kind of voltage by taking a type of water based electrolyte with high concentrations of a specific Lithium salt. This changed the chemistry of the battery and created a film around the anode electrode, something that had never happened in a water-based battery before. This kind of protective film is known as a Solid Electrolyte Interphase, which had only happened in non-aqueous electrolytes before.

These batteries were proven to be more stable than other aqueous batteries, achieving both cycling stability and high voltage without depending on each other or at the expanse of energy density.

We Don’t Know How Practical this Nanotechnology Is

Though the applications for this breakthrough are incredibly important, the scientific community isn’t yet aware of how realistically practical the discovery is. This breakthrough mostly opens up a door in nanotechnology that hadn’t ever been seen before, and further research and development can bring it to its full potential.

MIT: Forget Graphene and Carbon Nanotubes, Get Ready for Diamond Nanothread

The discovery of a stable form of one-dimensional diamond has scientists racing to understand its properties. The first signs are that diamond nanothread will be more versatile than anyone expected. What will this mean?

Hardly a week goes by without somebody proclaiming a new application for graphene, the form of carbon that occurs in single sheets with chicken wire-like structure (see “Research Hints at Graphene’s Photovoltaic Potential”). Roll a graphene sheet into a tube and it forms a carbon nanotube, another wonder material with numerous applications. And wrap it further into a ball and, with a small rearrangement of bonds, it forms buckyballs.

Now there is a new kid on the carbon block. Last month, a team at Pennsylvania State University and elsewhere announced they had created another type of carbon that takes the form of a one-dimensional diamond crystal capped with hydrogen. They call this new material diamond nanothread.

That caused a flurry of excitement and raised some interesting questions. Materials scientists are fascinated by the potential properties of a diamond nanothread and its applications. But one fear is that such a thread would be so brittle that it would shatter like glass under any kind of load, a property that would severely limit its use.

Today, we get some new insight into diamond nanothreads thanks to the work of Haifei Zhan at Queensland University of Technology in Australia and a few pals. These guys have modeled the threads using large-scale molecular dynamics simulations. And they conclude that the material could be more versatile than anyone thought. There are tentative signs that diamond nanothread could be a new a wonder material in its own right.

The Penn State team manufactured the nanothread from benzene molecules, simple rings of carbon atoms. It’s not hard to see how a stack of these could bond in a way that forms a thread.

And that’s exactly what the Penn State team did. They stacked the molecules into a line, placed it under pressure so that the molecules polymerized and, voila, created a diamond nanothread.

That sounds simple in theory but the complexity arises from the way the carbon atoms can bond. Various configurations are possible, and the question that Zhan and co investigate is how the properties of the thread depend on these arrangements.

In particular, Zhan and co look at the two most common configurations. The first is straightforward polymerized benzene—a stack of these rings bonded together. This is a rigid molecule that becomes increasingly brittle as it gets longer. Constructing anything complex with long sections of poly-benzene would be like trying to sew with like uncooked spaghetti.

But there is another configuration of carbon atoms known as Stone-Wales defects, and these are much more malleable. Indeed, the Stone-Wales defects act like hinges connecting sections of poly-benzene.

Zhan and co simulate how the properties of the nanothread vary as the density of these defects increases. And they conclude that when the density crosses a particular threshold, the thread suddenly changes from brittle to entirely flexible—rather like the difference between uncooked and cooked spaghetti.

That’s an interesting result. It implies that the property of the nanothread can be tuned simply by controlling the density of Stone-Wales defects along its length. So some parts of the thread can be made rigid, while others are entirely flexible.

What of potential applications? “Its highly tunable ductility together with its ultra-light density and high Young’s modulus makes diamond nanothread ideal for the creation of extremely strong three-dimensional nano-architectures,” say Zhan and co.

Of course, this work is just a simulation. There are almost certainly going to be differences between its predictions and the behavior of diamond nanothreads in the real world. So the next step will be for materials scientists to create some nanothread construction kits and start measuring this material’s properties for real.

Given the huge interest in carbon architecture and the vast sums of money being poured into this area—the European Union alone has a €1 billion research project focused purely on graphene—it surely won’t be long before we see diamond nanothreads in the flesh and some of the extraordinary applications that it should make possible.

Ref: arxiv.org/abs/1511.01583: From Brittle to Ductile: A Structure Dependent Ductility of Diamond Nanothread

 

Graphene’s stabilizling influence on Supercapacitors

Supercapacitors can be charged and discharged tens of thousands of times, but their relatively low energy density compared to conventional batteries limits their application for energy storage. Now, A*STAR researchers have developed an ‘asymmetric’ supercapacitor based on metal nitrides and graphene that could be a viable energy storage solution (“All Metal Nitrides Solid-State Asymmetric Supercapacitors”).

llustration of the asymmetric supercapacitor, consisting of vertically aligned graphene nanosheets coated with iron nitride and titanium nitride as the anode and cathode, respectively. (©WILEY-VCH Verlag)

A supercapacitor’s viability is largely determined by the materials of which its anodes and cathodes are comprised. These electrodes must have a high surface area per unit weight, high electrical conductivity and capacitance and be physically robust so they do not degrade during operation in liquid or hostile environments.

Unlike traditional supercapacitors, which use the same material for both electrodes, the anode and cathode in an asymmetric supercapacitor are made up of different materials. Scientists initially used metal oxides as asymmetric supercapacitor electrodes, but, as metal oxides do not have particularly high electrical conductivities and become unstable over long operating cycles, it was clear that a better alternative was needed.

Metal nitrides such as titanium nitride, which offer both high conductivity and capacitance, are a promising alternative, but they tend to oxidize in watery environments that limits their lifetime as an electrode. A solution to this is to combine them with more stable materials.

Hui Huang from A*STAR’s Singapore Institute of Manufacturing Technology and his colleagues from Nanyang Technological University and Jinan University, China, have fabricated asymmetric supercapacitors which incorporate metal nitride electrodes with stacked sheets of graphene.

To get the maximum benefit from the graphene surface, the team used a precise method for creating thin-films, a process known as atomic layer deposition, to grow two different materials on vertically aligned graphene nanosheets: titanium nitride for their supercapacitor’s cathode and iron nitride for the anode. The cathode and anode were then heated to 800 and 600 degrees Celsius respectively, and allowed to slowly cool. The two electrodes were then separated in the asymmetric supercapacitor by a solid-state electrolyte, which prevented the oxidization of the metal nitrides.

The researchers tested their supercapacitor devices and showed they could cycle 20,000 times and exhibited both high capacitance and high power density. “These improvements are due to the ultra-high surface area of the vertically aligned graphene substrate and the atomic layer deposition method that enables full use of it,” says Huang. “In future research, we want to enlarge the working-voltage of the device to increase energy density further still,” says Huang.

Source: A*STAR

Read more: Graphene’s stabilizling influence on supercapacitors

Ultrasensitive sensors: Boron-doped Graphene

Ultrasensitive gas sensors based on the infusion of boron atoms into graphene—a tightly bound matrix of carbon atoms—may soon be possible, according to an international team of researchers from six countries.

Graphene is known for its remarkable strength and ability to transport electrons at high speed, but it is also a highly sensitive gas sensor. With the addition of boron atoms, the boron graphene sensors were able to detect noxious gas molecules at extremely low concentrations, parts per billion in the case of nitrogen oxides and parts per million for ammonia, the two gases tested to date. This translates to a 27 times greater sensitivity to nitrogen oxides and 10,000 times greater sensitivity to ammonia compared to pristine graphene. The researchers believe these results, reported today (Nov. 2) in the Proceedings of the National Academy of Sciences, will open a path to high-performance sensors that can detect trace amounts of many other molecules.

“This is a project that we have been pursuing for the past four years, ” said Mauricio Terrones, professor of physics, chemistry and materials science at Penn State. “We were previously able to dope graphene with atoms of nitrogen, but boron proved to be much more difficult. Once we were able to synthesize what we believed to be boron graphene, we collaborated with experts in the United States and around the world to confirm our research and test the properties of our material.”

Both boron and nitrogen lie next to carbon on the periodic table, making their substitution feasible. But boron compounds are very air sensitive and decompose rapidly when exposed to the atmosphere. One-centimeter-square sheets were synthesized at Penn State in a one-of-a-kind bubbler-assisted chemical vapor deposition system. The result was large-area, high-quality boron-doped graphene sheets.

Once fabricated, the researchers sent boron graphene samples to researchers at the Honda Research Institute USA Inc., Columbus, Ohio, who tested the samples against their own highly sensitive gas sensors. Konstantin Novoselov’s lab at the University of Manchester, UK, studied the transport mechanism of the sensors. Novoselov was the 2010 Nobel laureate in physics. Theory collaborators in the U.S. and Belgium matched the scanning tunneling microscopy images to experimental images, confirmed the presence of the boron atoms in the graphene lattice and their effect when interacting with ammonia or nitrogen oxide molecules. Collaborators in Japan and China also contributed to the research.

“This multidisciplinary research paves a new avenue for further exploration of ultrasensitive gas sensors,” said Avetik Harutyunyan, chief scientist and project leader at Honda Research Institute USA Inc. “Our approach combines novel nanomaterials with continuous ultraviolet light radiation in the sensor design that have been developed in our laboratory by lead researcher Dr. Gugang Chen in the last five years. We believe that further development of this technology may break the parts per quadrillion level of detection limit, which is up to six orders of magnitude better sensitivity than current state-of-the-art sensors.”

These sensors can be used for labs and industries that use ammonia, a highly corrosive health hazard, or to detect nitrogen oxides, a dangerous atmospheric pollutant emitted from automobile tailpipes. In addition to detecting toxic or flammable gases, theoretical work indicates that boron-doped graphene could lead to improved lithium-ion batteries and field-effect transistors, the authors report.

Explore further: Study opens graphene band-gap

More information: Ultrasensitive gas detection of large-area boron-doped graphene, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1505993112

Journal reference: Proceedings of the National Academy of Sciences

 

 

Research at the Univeristy of Exeter boosts graphene revolution

Pioneering new research by the Univ. of Exeter could pave the way for miniaturized optical circuits and increased internet speeds, by helping accelerate the ‘graphene revolution’.

Physicists from the Univ. of Exeter in collaboration with the ICFO Institute in Barcelona have used a ground-breaking new technique to trap light at the surface of the wonder material graphene using only pulses of laser light.

Crucially, the team of scientists have also been able to steer this trapped light across the surface of the graphene, without the need for any nanoscale devices. This dual breakthrough opens up a host of opportunities for advances in pivotal electronic products, such as sensors and miniaturized integrated circuits.

The new research features in the latest online edition of the respected scientific journal, Nature Physics.

Dr. Tom Constant, lead author on the paper and part of Exeter’s Physics and Astronomy Department said: ” This new research has the potential to give us invaluable insight into the wonder material and how it interacts with light. A more immediate commercial application could be a simple device that could easily scan a piece of graphene and tell you some key properties like conductivity, resistance and purity .”

Dr. Constant and his colleagues used pulses of light to be able to trap the light on the surface of commercially-available graphene. When trapped, the light converts into a quasi-particle called a ‘surface plasmon’, a mixture of both light and the graphene’s electrons.

Additionally, the team have demonstrated the first example of being able to steer the plasmons around the surface of the graphene, without the need to manufacture complicated nanoscale systems. The ability both to trap light at a surface, and direct it easily, opens up new opportunities for a number of electronic-based devices, as well as help to bridge the gap between the electronics and light.

Dr. Constant said: “Computers than can use light as part of their infrastructure have the potential to show significant improvement. Any advance that reveals more about light’s interaction with graphene-based electronics will surely benefit the computers or smartphones of the future.”

Source: Univ. of Exeter

MIT: A “Shocking” New Way to “Desalinate” – No Membranes and Less Energy

As the availability of clean, potable water becomes an increasingly urgent issue in many parts of the world, researchers are searching for new ways to treat salty, brackish or contaminated water to make it usable. Now a team at MIT has come up with an innovative approach that, unlike most traditional desalination systems, does not separate ions or water molecules with filters, which can become clogged, or boiling, which consumes great amounts of energy.

Instead, the system uses an electrically driven shockwave within a stream of flowing water, which pushes salty water to one side of the flow and fresh water to the other, allowing easy separation of the two streams. The new approach is described in the journal Environmental Science and Technology Letters, in a paper by professor of chemical engineering and mathematics Martin Bazant, graduate student Sven Schlumpberger, undergraduate Nancy Lu, and former postdoc Matthew Suss.

This approach is “a fundamentally new and different separation system,” Bazant says. And unlike most other approaches to desalination or water purification, he adds, this one performs a “membrane-less separation” of ions and particles.

Membranes in traditional desalination systems, such as those that use reverse osmosis or electrodialysis, are “selective barriers,” Bazant explains: They allow molecules of water to pass through, but block the larger sodium and chlorine atoms of salt. Compared to conventional electrodialysis, “This process looks similar, but it’s fundamentally different,” he says.

In the new process, called shock electrodialysis, water flows through a porous material —in this case, made of tiny glass particles, called a frit — with membranes or electrodes sandwiching the porous material on each side. When an electric current flows through the system, the salty water divides into regions where the salt concentration is either depleted or enriched. When that current is increased to a certain point, it generates a shockwave between these two zones, sharply dividing the streams and allowing the fresh and salty regions to be separated by a simple physical barrier at the center of the flow.

“It generates a very strong gradient,” Bazant says.

Even though the system can use membranes on each side of the porous material, Bazant explains, the water flows across those membranes, not through them. That means they are not as vulnerable to fouling — a buildup of filtered material — or to degradation due to water pressure, as happens with conventional membrane-based desalination, including conventional electrodialysis. “The salt doesn’t have to push through something,” Bazant says. The charged salt particles, or ions, “just move to one side,” he says.

The underlying phenomenon of generating a shockwave of salt concentration was discovered a few years ago by the group of Juan Santiago at Stanford University. But that finding, which involved experiments with a tiny microfluidic device and no flowing water, was not used to remove salt from the water, says Bazant, who is currently on sabbatical at Stanford.

The new system, by contrast, is a continuous process, using water flowing through cheap porous media, that should be relatively easy to scale up for desalination or water purification. “The breakthrough here is the engineering [of a practical system],” Bazant says.

One possible application would be in cleaning the vast amounts of wastewater generated by hydraulic fracturing, or fracking. This contaminated water tends to be salty, sometimes with trace amounts of toxic ions, so finding a practical and inexpensive way of cleaning it would be highly desirable. This system not only removes salt, but also a wide variety of other contaminants — and because of the electrical current passing through, it may also sterilize the stream. “The electric fields are pretty high, so we may be able to kill the bacteria,” Schlumpberger says.

The research produced both a laboratory demonstration of the process in action and a theoretical analysis that explains why the process works, Bazant says. The next step is to design a scaled-up system that could go through practical testing.

Initially at least, this process would not be competitive with methods such as reverse osmosis for large-scale seawater desalination. But it could find other uses in the cleanup of contaminated water, Schlumpberger says.

Unlike some other approaches to desalination, he adds, this one requires little infrastructure, so it might be useful for portable systems for use in remote locations, or for emergencies where water supplies are disrupted by storms or earthquakes.

Maarten Biesheuvel, a principal scientist at the Netherlands Water Technology Institute who was not involved in this research, says the work “is of very high significance to the field of water desalination. It opens up a whole range of new possibilities for water desalination, both for seawater and brackish water resources, such as groundwater.”

Biesheuvel adds that this team “shows a radically new design where within one and the same channel ions are separated between different regions. … I expect that this discovery will become a big ‘hit’ in the academic field. … It will be interesting to see whether the upscaling of this technology, from a single cell to a stack of thousands of cells, can be achieved without undue problems.”

The research was supported by the MIT Energy Initiative, Weatherford International, the USA-Israel Binational Science Foundation, and the SUTD-MIT Graduate Fellows Program.

Source: Massachusetts Institute of Technology

 

Nanopores could be the Solution for Taking the “Salt” out of Seawater

University of Illinois engineers have found an energy-efficient material for removing salt from seawater that could provide a rebuttal to poet Samuel Taylor Coleridge’s lament, “Water, water, every where, nor any drop to drink.”

The material, a nanometer-thick sheet of molybdenum disulfide (MoS2) riddled with tiny holes called nanopores, is specially designed to let high volumes of water through but keep salt and other contaminates out, a process called desalination. In a study published in the journal Nature Communications (“Water desalination with a single-layer MoS2 nanopore”), the Illinois team modeled various thin-film membranes and found that MoS2 showed the greatest efficiency, filtering through up to 70 percent more water than graphene membranes.

A computer model of a nanopore in a single-layer sheet of MoS2 shows that high volumes of water can pass through the pore using less pressure than standard plastic membranes. Salt water is shown on the left, fresh water on the right. (Image: Mohammad Heiranian)

“Even though we have a lot of water on this planet, there is very little that is drinkable,” said study leader Narayana Aluru, a U. of I. professor of mechanical science and engineering. “If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis.

“Finding materials for efficient desalination has been a big issue, and I think this work lays the foundation for next-generation materials. These materials are efficient in terms of energy usage and fouling, which are issues that have plagued desalination technology for a long time,” said Aluru, who also is affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.

Most available desalination technologies rely on a process called reverse osmosis to push seawater through a thin plastic membrane to make fresh water. The membrane has holes in it small enough to not let salt or dirt through, but large enough to let water through. They are very good at filtering out salt, but yield only a trickle of fresh water. Although thin to the eye, these membranes are still relatively thick for filtering on the molecular level, so a lot of pressure has to be applied to push the water through.

“Reverse osmosis is a very expensive process,” Aluru said. “It’s very energy intensive. A lot of power is required to do this process, and it’s not very efficient. In addition, the membranes fail because of clogging. So we’d like to make it cheaper and make the membranes more efficient so they don’t fail as often. We also don’t want to have to use a lot of pressure to get a high flow rate of water.”

One way to dramatically increase the water flow is to make the membrane thinner, since the required force is proportional to the membrane thickness. Researchers have been looking at nanometer-thin membranes such as graphene. However, graphene presents its own challenges in the way it interacts with water.

Aluru’s group has previously studied MoS2 nanopores as a platform for DNA sequencing and decided to explore its properties for water desalination. Using the Blue Waters supercomputer at the National Center for Supercomputing Applications at the U. of I., they found that a single-layer sheet of MoS2 outperformed its competitors thanks to a combination of thinness, pore geometry and chemical properties.

A MoS2 molecule has one molybdenum atom sandwiched between two sulfur atoms. A sheet of MoS2, then, has sulfur coating either side with the molybdenum in the center. The researchers found that creating a pore in the sheet that left an exposed ring of molybdenum around the center of the pore created a nozzle-like shape that drew water through the pore.

“MoS2 has inherent advantages in that the molybdenum in the center attracts water, then the sulfur on the other side pushes it away, so we have much higher rate of water going through the pore,” said graduate student Mohammad Heiranian, the first author of the study. “It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalize the pore, which is a very complex process with graphene.”

In addition to the chemical properties, the single-layer sheets of MoS2 have the advantages of thinness, requiring much less energy, which in turn dramatically reduces operating costs. MoS2 also is a robust material, so even such a thin sheet is able to withstand the necessary pressures and water volumes.

The Illinois researchers are establishing collaborations to experimentally test MoS2 for water desalination and to test its rate of fouling, or clogging of the pores, a major problem for plastic membranes. MoS2 is a relatively new material, but the researchers believe that manufacturing techniques will improve as its high performance becomes more sought-after for various applications.

“Nanotechnology could play a great role in reducing the cost of desalination plants and making them energy efficient,” said Amir Barati Farimani, who worked on the study as a graduate student at Illinois and is now a postdoctoral fellow at Stanford University. “I’m in California now, and there’s a lot of talk about the drought and how to tackle it. I’m very hopeful that this work can help the designers of desalination plants. This type of thin membrane can increase return on investment because they are much more energy efficient.”

Source: University of Illinois at Urbana-Champaign

Vanderbilt University: Quantum Dots Made from Fool’s Gold Boost Battery Performance

IMAGE: Vanderbilt graduate student Anna Douglas holding one of the batteries that she has modified by adding millions of quantum dots made from iron pyrite, fool’s gold. view more

Credit: John Russell, Vanderbilt University

If you add quantum dots – nanocrystals 10,000 times smaller than the width of a human hair – to a smartphone battery it will charge in 30 seconds, but the effect only lasts for a few recharge cycles.

However, a group of researchers at Vanderbilt University report in the Nov. 11 issue of the journal ACS Nano that they have found a way to overcome this problem: Making the quantum dots out of iron pyrite, commonly known as fool’s gold, can produce batteries that charge quickly and work for dozens of cycles.

The research team headed by Assistant Professor of Mechanical Engineering Cary Pint and led by graduate student Anna Douglas became interested in iron pyrite because it is one of the most abundant materials in the earth’s surface. It is produced in raw form as a byproduct of coal production and is so cheap that it is used in lithium batteries that are bought in the store and thrown away after a single use.

Despite all their promise, researchers have had trouble getting nanoparticles to improve battery performance.

“Researchers have demonstrated that nanoscale materials can significantly improve batteries, but there is a limit,” Pint said. “When the particles get very small, generally meaning below 10 nanometers (40 to 50 atoms wide), the nanoparticles begin to chemically react with the electrolytes and so can only charge and discharge a few times. So this size regime is forbidden In commercial lithium-ion batteries.”

Aided by Douglas’ expertise in synthesizing nanoparticles, the team set out to explore this “ultrasmall” regime. They did so by adding millions of iron pyrite quantum dots of different sizes to standard lithium button batteries like those that are used to power watches, automobile key remotes and LED flashlights. They got the most bang for their buck when they added ultrasmall nanocrystals that were about 4.5 nanometers in size. These substantially improved both the batteries’ cycling and rate capabilities.

The researchers discovered that they got this result because iron pyrite has a unique way of changing form into an iron and a lithium-sulfur (or sodium sulfur) compound to store energy. “This is a different mechanism from how commercial lithium-ion batteries store charge, where lithium inserts into a material during charging and is extracted while discharging – all the while leaving the material that stores the lithium mostly unchanged,” Douglas explained.

According to Pint, “You can think of it like vanilla cake. Storing lithium or sodium in conventional battery materials is like pushing chocolate chips into the cake and then pulling the intact chips back out. With the interesting materials we’re studying, you put chocolate chips into vanilla cake and it changes into a chocolate cake with vanilla chips.”

As a result, the rules that forbid the use of ultrasmall nanoparticles in batteries no longer apply. In fact, the scales are tipped in favor of very small nanoparticles.

“Instead of just inserting lithium or sodium ions in or out of the nanoparticles, storage in iron pyrite requires the diffusion of iron atoms as well. Unfortunately, iron diffuses slowly, requiring that the size be smaller than the iron diffusion length – something that is only possible with ultrasmall nanoparticles,” Douglas explained.

A key observation of the team’s study was that these ultrasmall nanoparticles are equipped with dimensions that allow the iron to move to the surface while the sodium or lithium reacts with the sulfurs in the iron pyrite. They demonstrated that this isn’t the case for larger particles, where the inability of the iron to move through the iron pyrite materials limits their storage capability.

Pint believes that understanding of chemical storage mechanisms and how they depend on nanoscale dimensions is critical to enable the evolution of battery performance at a pace that stands up to Moore’s law and can support the transition to electric vehicles.

“The batteries of tomorrow that can charge in seconds and discharge in days will not just use nanotechnology, they will benefit from the development of new tools that will allow us to design nanostructures that can stand up to tens of thousands of cycles and possess energy storage capacities rivaling that of gasoline,” said Pint. “Our research is a major step in this direction.”

###

Coauthors of the paper with Pint and Douglas include mechanical engineering graduate students Rachel Carter and Adam Cohn and interdisciplinary materials science graduate students Keith Share and Landon Oakes. The research was funded in part by National Science Foundation grant EPS 1004083 and NSF’s graduate research fellowship program grant 1445197.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

GE: 3D Printed Steam Turbine May Make Desalination Cost Effective

The mini desalination system combines 3D printing with GE’s deep reservoir of knowledge of turbo-machinery and fluid dynamics. GE scientists Doug Hofer and Vitali Lissianski used them to shrink a power generation steam turbine that would normally barely fit inside a school gym.

Not too long ago, Lissianski, a chemical engineer in the Energy Systems Lab at GE Global Research, was chatting with his lab manager about new ideas for water desalination. This type of “small talk” happens thousand times a day at the GRC.

Their lab tackles a lot of technical challenges coming from GE’s industrial businesses including Power and Water, Oil and Gas, Aviation and Transportation, and they quickly hit on a possible solution.

It led them to Hofer. As a senior principal engineer for aero systems at GRC and a steam turbine specialist, he was part of another team of GE researchers working on a project for Oil and Gas to improve small scale liquefied natural gas (LNG) production. A key part of the project focused on using 3D printing to miniaturize the turbo expander modeled after a GE steam turbine. (A turbo-expander is a machine that expands pressurized gas so that it could be used for work.)

Hofer was the perfect person in charge. He led the steam turbine aero team at Power and Water before coming to GRC eight years ago. Few people in the world have the kind of expertise and knowledge of steam turbine technology that Doug brings. “In traditional steam turbines, steam condenses and turns to water,” he says. “We thought maybe the same principle could be applied to water desalination.”

The only difference, Hofer explained, would be in using flows through the turbine to freeze the brine, or salt water instead of condensing the steam to water as in a steam turbine. Freezing the brine would naturally separate the salt and water by turning salt into a solid and water to ice.

A 3D printed mini-turbine. Image credit: GE Reports

Lissianski and Hofer compared notes and today they are working on a new project with the US Department of Energy to test their new water desalination concept.

The reality today is that 97.5 percent of the world’s potential clean water drinking supply essentially remains untapped, locked in salty oceans and unsuitable for human consumption. This is in the face of growing global water shortage. According to the United Nations, water scarcity impacts 1.2 billion people, or one fifth of the world’s population.

Not even the United States has been spared. California, which has one of the country’s longest coastlines bordering the ocean, has been suffering through a severe water shortage crisis.

Technology inspired by a miniaturized steam turbine could help change all that. And there’s no reason to believe that it can’t. Advances in miniaturization have proven to have great impact time and time again.

For example, the application of Moore’s Law in the semiconductor world has shrunk the size of computer chips to enable mobile phones that pack more computing power than a roomful of mainframe supercomputers that were state-of-the-art just a few decades ago.

In ultrasound, miniaturization technologies have shrunk consoles to the size of a phone screen and can fit neatly into a doctor’s coat pocket. Doctors today can deliver high quality care in regions where access was previously limited or non-existent.

And steam turbines? They already have proven to be one of the key innovations that spread electricity to virtually every home and business. Miniaturized, they just might hold the key to spreading water desalination around the world.

Top image: Doug Hofer, a GE steam turbine specialist, and Vitali Lissianski, a chemical engineer in GE’s Energy Systems Lab, holding the mini-turbine in front of an actual size power generation steam turbine. Image credit: GE Reports

Making Desalination Cheaper and More Efficient – MIT Researcher Applies New Materials to Research

With the intensifying drought in California, the state has accelerated the construction of desalination plants. Yet due to high construction and operating costs, as well as environmental concerns, we’re not likely to see reclaimed seawater represent more than a small fraction of America’s clean water reserves for some time to come. Aside from other costs, the immense amounts of energy required to make clean water from seawater continues to make desalination a niche solution in most parts of the world.

When Jeffrey Grossman, a professor at MIT’s Department of Materials Science and Engineering (DMSE), began looking into whether new materials might reduce the cost of desalination, he was surprised to find how little research and development money was being applied to the problem.

“A billion people around the world lack regular access to clean water, and that’s expected to more than double in the next 25 years,” Grossman says. “Desalinated water costs five to 10 times more than regular municipal water, yet we’re not investing nearly enough money into research. If we don’t have clean energy we’re in serious trouble, but if we don’t have water we die.”

At the Grossman Group, which explores the development of new materials to address clean energy and water problems, a possible solution may be at hand. Grossman’s lab has demonstrated strong results showing that new filters made from graphene could greatly improve the energy efficiency of desalination plants while potentially reducing other costs as well.

Graphene, which results from slicing off an atom-thick layer of graphite, is increasingly emerging as something of a wonder material. The Grossman Group, for example, is also looking into using it as a cheaper alternative to silicon for making solar cells.

“It’s never been a more exciting time to be a materials scientist,” says Grossman. “When you look at clean tech or water filtration, you find that the energy conversion bottleneck stems from the material. We can now design materials pretty much all the way down to the scale of the atom in almost any way we want, tailoring materials in ways that were previously impossible. There’s a convergence emerging in which we are facing enormously pressing problems that can only be solved by developing new materials.”

Graphene filters: Up to 50 percent less energy

First isolated in 2003, graphene has different electrical, optical, and mechanical properties than graphite. “It’s stronger than steel, and it has unique sieving properties,” Grossman says. At only an atom thick, there’s far less friction loss when you push seawater through a perforated graphene filter compared with the polyamide plastic filters that have been used for the last 50 years, he says.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

Yet, significant challenges remain in bringing down costs. The Grossman Group has made good progress in creating high volumes of graphene at a reasonably low cost. A more serious challenge, however, is cost-effectively poking uniform holes in the graphene in a highly scalable manner.

“A typical plant has tens of thousands of membranes, configured in two-meter long tubes, each of which has 40 square meters of rolled up active membrane,” Grossman says. “We have to match that volume at the same cost, or it’s a nonstarter.”

Making graphene on the cheap

The traditional way to make graphene—since its first isolation in 2003, mind you—is to peel it off with adhesive. “You literally take a piece of Scotch Tape to graphite and you peel,” Grossman explains. “If you keep doing this, you eventually wind up with a single layer. The problem is it would take forever to peel off enough graphene for a desalination plant.”

Another approach is to “grow” graphene by applying super-hot gases to copper foil. “Growing graphene provides the best quality, which is why the semiconductor industry is interested in it,” Grossman says. The process, however, is very expensive and energy-intensive.

Instead, the Grossman Group is using a much more affordable chemical approach, which produces sufficient quality for creating desalination membranes. “Fortunately, our application doesn’t require the best quality,” says Grossman. “With the chemical technique, we put graphite in a solution, and apply low temperature chemistry to break apart the entire chunk of graphite into sheets. We can get lots of graphene very cheaply and quickly.”

Creating pores that block salt but let water molecules pass is a steeper challenge. The reason desalination is possible in the first place is that when diffused in water, salt ions bond with water molecules, thereby creating a larger entity. But the difference in size compared to a free water molecule is still frustratingly small.

“The challenge is to find the sweet spot of about 0.8 nanometers,” Grossman says. “If your pores are at 1.5 nm, then both the water and salt will pass through. If they’re half a nanometer, then nothing gets through.”

A 0.8 nm hole is “smaller than we’ve ever been able to make in a controllable way with any other material,” Grossman says. “And we need to do this over a very large area very consistently and cheaply.”

The Grossman Group is pursuing three techniques to make nanoporous graphene membranes, all of which use chemical and thermal energy rather than mechanical processes. “If you tried to use lithography, it would take years,” Grossman says. “Our first approach involves making the holes too big, and then carefully filling them in. Another tries to make them exactly the right size, and the third involves starting with a material without holes and then carefully ripping it apart.”

The chemical technique for making graphene actually produces graphene oxide, which is considered undesirable for semiconductors, but is fine for filters. As a result, the researchers were able to avoid the difficult step of removing the oxygen from the graphene oxide. In fact, they found a way to use the oxygen to their advantage.

“By controlling the way the oxygen is bonded to the graphene sheet, we can use chemical and thermal energy to drill the holes with the help of the oxygen,” Grossman says.

First target: Brackish water

As the Grossman Group continues to work on the challenge of manufacturing and perforating graphene sheets, Grossman is looking to leverage other benefits of graphene filters to help bring the technology to market.

Although graphene should improve efficiency with seawater and the even saltier, dirtier water used in hydraulic fracturing, it will likely debut in plants that clean brackish water, such as found in estuaries. “It turns out that higher permeability even by a factor of two or three would make a bigger difference with brackish water than with seawater,” Grossman says. “You lower the energy consumption in both cases, but more so for brackish water.”

Graphene filters could also enable the construction of smaller, cheaper plants. “With graphene you have more choices in how you operate the plant,” Grossman says. “You could apply the same pressures but get more water out, or you could operate it at lower pressures and get the same amount of water, but at a lower energy cost.”

Grossman notes that it can take years or even decades to site and permit a plant in heavily populated coastal areas. “A lot of effort goes into how you’re going to build the plant and where you’re going to find enough land,” Grossman says. “Having the option to build a smaller plant would be a big advantage.”

Explore further: Nanoporous graphene could outperform best commercial water desalination techniques

Provided by: Massachusetts Institute of Technology