03 Mar 2016
“Our climate change solution is two fold: To transform the greenhouse gas carbon dioxide into valuable products and to provide greenhouse gas emission-free alternatives to today’s industrial and transportation fossil fuel processes,” Stuart Licht, professor of chemistry at George Washington University
An interdisciplinary team of scientists has worked out a way to make electric vehicles that are not only carbon neutral, but carbon negative, capable of actually reducing the amount of atmospheric carbon dioxide as they operate. They have done so by demonstrating how the graphite electrodes used in the lithium-ion batteries that power electric automobiles can be replaced with carbon material recovered from the atmosphere.
The recipe for converting carbon dioxide gas into batteries is described in a paper published in the March 2 issue of the journal ACS Central Science (“Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes”).
The Solar Thermal Electrochemical Process (STEP) converts atmospheric carbon dioxide into carbon nanotubes that can be used in advanced batteries. (Image: Julie Turner, Vanderbilt University)
“Our climate change solution is two fold: To transform the greenhouse gas carbon dioxide into valuable products and to provide greenhouse gas emission-free alternatives to today’s industrial and transportation fossil fuel processes,” Stuart Licht, professor of chemistry at George Washington University said.
“In addition to better batteries other applications for the carbon nanotubes include carbon composites for strong, lightweight construction materials, sports equipment and car, truck and airplane bodies.” The unusual pairing of carbon dioxide conversion and advanced battery technology is the result of a collaboration between Dr. Licht, and the laboratory of assistant professor of mechanical engineering Cary Pint at Vanderbilt University. Licht adapted the lab’s solar thermal electrochemical process (STEP) so that it produces carbon nanotubes from carbon dioxide and with Pint by incorporating them into both lithium-ion batteries like those used in electric vehicles and electronic devices and low-cost sodium-ion batteries under development for large-scale applications, such as the electric grid. In lithium-ion batteries, the nanotubes replace the carbon anode used in commercial batteries.
The team demonstrated that the carbon nanotubes gave a small boost to the performance, which was amplified when the battery was charged quickly. In sodium-ion batteries, the researchers found that small defects in the carbon, which can be tuned by STEP, can unlock stable storage performance over 3.5 times above that of sodium-ion batteries with graphite electrodes. Most importantly, both carbon-nanotube batteries were exposed to about 2.5 months of continuous charging and discharging and showed no sign of fatigue.
Published on Feb 25, 2016: Video interview with Cary Pint explaining this research.
Scientists from Vanderbilt and George Washington universities have worked out a way to make electric vehicles not just carbon neutral but carbon negative by demonstrating how the graphite electrodes used in the lithium-ion batteries can be replaced with carbon recovered from the atmosphere.
|“This trailblazing research has achieved yet another amazing milestone with the incorporation of the carbon nanotubes produced by Stuart Licht’s STEP reduction of carbon dioxide process into batteries for electric vehicles and large scale storage,” said Michael King, chair of GW’s Department of Chemistry. “We are thrilled by this translation of basic research into potentially useful consumer products while mitigating atmospheric carbon dioxide buildup. This is a win-win for everyone!”|
|The researchers estimate that with a battery cost of $325 per kWh (the average cost of lithium-ion batteries reported by the Department of Energy in 2013), a kilogram of carbon dioxide has a value of about $18 as a battery material – six times more than when it is converted to methanol – a number that only increases when moving from large batteries used in electric vehicles to the smaller batteries used in electronics.
And unlike methanol, combining batteries with solar cells provides renewable power with zero greenhouse emissions, which is needed to put an end to the current carbon cycle that threatens future global sustainability.
|Licht also proposes a modified flue system for combustion plants that incorporates this process could be self-sustaining, as exemplified by a new natural gas power plant with zero carbon dioxide emissions. That’s because the side product of the process is pure oxygen, which plants could then use for further combustion. The calculated total cost per metric tonne of CNTs would be much less expensive than current synthetic methods.|
|“This approach not only produces better batteries but it also establishes a value for carbon dioxide recovered from the atmosphere that is associated with the end-user battery cost unlike most efforts to reuse CO2 that are aimed at low-valued fuels, like methanol, that cannot justify the cost required to produce them,” said Pint.|
|Source: Vanderbilt University|
Genesis Nanotechnology, Inc. ~ “Great Things from Small Things”
18 Feb 2016
University of Texas at Arlington chemists have developed new high-performing materials for cells that harness sunlight to split carbon dioxide and water into usable fuels like methanol and hydrogen gas. These “green fuels” can be used to power cars, home appliances or even to store energy in batteries.
“Technologies that simultaneously permit us to remove greenhouse gases like carbon dioxide while harnessing and storing the energy of sunlight as fuel are at the forefront of current research,” said Krishnan Rajeshwar, UTA distinguished professor of chemistry and biochemistry and co-founder of the University’s Center of Renewable Energy, Science and Technology.
“Our new material could improve the safety, efficiency and cost-effectiveness of solar fuel generation, which is not yet economically viable,” he added.
The new hybrid platform uses ultra-long carbon nanotube networks with a homogeneous coating of copper oxide nanocrystals. It demonstrates both the high electrical conductivity of carbon nanotubes and the photocathode qualities of copper oxide, efficiently converting light into the photocurrents needed for the photoelectrochemical reduction process.
Morteza Khaledi, dean of the UTA College of Science, said Rajeshwar’s work is representative of the University’s commitment to addressing critical issues with global environmental impact under the Strategic Plan 2020.
“Dr. Rajeshwar’s ongoing, global leadership in research focused on solar fuel generation forms part of UTA’s increasing focus on renewable and sustainable energy,” Khaledi said. “Creating inexpensive ways to generate fuel from an unwanted gas like carbon dioxide would be an enormous step forward for us all.”
For the solar fuel cells project, Rajeshwar worked with Csaba Janáky, an assistant chemistry professor at the University of Szeged in Hungary and Janáky’s master’s student Egon Kecsenovity. Janaky served as a UTA Marie Curie Fellow from 2011 to 2013.
The findings are the subject of a Feb. 15 minireview, “Electrodeposition of Inorganic Oxide/Nanocarbon Composites: Opportunities and Challenges,” published in ChemElectroChem Europe and a companion article in the Journal of Materials Chemistry A on “Decoration of ultra long carbon nanotubes with Cu2O nanocrystals: a hybrid platform for photoelectrochemical CO2 reduction.”
“The performance of our hybrid has proved far superior to the properties of the individual materials,” Rajeshwar said. “These new hybrid films demonstrate five-fold higher electrical conductivity compared to their copper oxide counterparts, and generate a three-fold increase in the photocurrents needed for the reduction process.”
The new material also demonstrates much greater stability during long-term photoelectrolysis than pure copper oxide, which corrodes over time, forming metallic copper.
The research involved developing a multi-step electrodeposition process to ensure that a homogeneous coating of copper oxide nanoparticles were deposited on the carbon nanotube networks. By varying the thickness of the carbon nanotube film and the amount of electrodeposited copper oxide, the researchers were able to optimize the efficiency of this new hybrid material.
Rajeshwar also is working with Brian Dennis, a UTA associate professor of mechanical and aerospace engineering, and Norma Tacconi, a research associate professor of chemistry and biochemistry, on a project with NASA to develop improved methods for oxygen recovery and reuse aboard human spacecraft.
The team is designing, building and demonstrating a “microfluidic electrochemical reactor” to recover oxygen from carbon dioxide extracted from cabin air. The prototype will be built over the next months at the Center for Renewable Energy Science and Technology at UTA.
Rajeshwar joined the College of Science in 1983, is a charter member of the UTA Academy of Distinguished Scholars and senior vice president of The Electrochemical Society, an organization representing the nation’s premier researchers who are dedicated the advancing solid state, electrochemical science and technology.
He is an expert in photoelectrochemistry, nanocomposites, electrochemistry and conducting polymers, and has received numerous awards, including the Wilfred T. Doherty Award from the American Chemical Society and the Energy Technology Division Research Award of the Electrochemical Society.
Rajeshwar earned his Ph.D. in chemistry from the Indian Institute of Science in Bangalore, India, and completed his post-doctoral training in Colorado State University.
- E. Kecsenovity, B. Endrődi, Zs. Pápa, K. Hernádi, K. Rajeshwar, C. Janáky. Decoration of ultra-long carbon nanotubes with Cu2O nanocrystals: a hybrid platform for enhanced photoelectrochemical CO2reduction. J. Mater. Chem. A, 2016; 4 (8): 3139 DOI:10.1039/C5TA10457B
08 Feb 2016
Iron-dotted boron nitride nanotubes, made in Yoke Khin Yaps’ lab at Michigan Tech, could make for better wearable tech because of their flexibility and electronic behaviors.
February 5, 2016—
The road to more versatile wearable technology is dotted with iron. Specifically, quantum dots of iron arranged on boron nitride nanotubes (BNNTs). The new material is the subject of a studypublished in Scientific Reports in February, led by Yoke Khin Yap, a professor of physics at Michigan Technological University.
Yap says the iron-studded BNNTs are pushing the boundaries of electronics hardware. The transistors modulating electron flow need an upgrade.
“Look beyond semiconductors,” he says, explaining that materials like silicon semiconductors tend to overheat, can only get so small and leak electric current. The key to revamping the fundamental base of transistors is creating a series of stepping-stones.
The nanotubes are the mainframe of this new material. BNNTs are great insulators and terrible at conducting electricity. While at first that seems like an odd choice for electronics, the insulating effect of BNNTs is crucial to prevent current leakage and overheating. Additionally, electron flow will only occur across the metal dots on the BNNTs.
In past research, Yap and his team used gold for quantum dots, placed along a BNNT in a tidy line. With enough energy potential, the electrons are repelled by the insulating BNNT and hopscotch from gold dot to gold dot. This electron movement is called quantum tunneling.
“Imagine this as a river, and there’s no bridge; it’s too big to hop over,” Yap says. “Now, picture having stepping stones across the river—you can cross over, but only when you have enough energy to do so.”
Nanotech for Wearable Electronics
Unlike with semiconductors, there is no classical resistance with quantum tunneling. No resistance means no heat. Plus, these materials are very small; the nanomaterials enable the transistors to shrink as well. An added bonus is that BNNTs are also quite flexible, a boon for wearable electronics.
“Here’s where the challenge comes in,” Yap says, holding up a pen to demonstrate. He gestures along the length of the pen, which mimics a straight BNNT, tapping out a line of quantum dots. “We have an array here to do quantum tunneling, but what if we want to bend the array to be flexible like a piece of wearable electronics?”
Yap sets down the pen and curls up his index finger: “And if I bend the dots, the distance between them changes—in doing so, we change the electronic behavior.”
Changing the behavior means that the quantum tunneling may not work. The solution is to get out of line: Yap and his team arranged a grid of quantum dots around the outside of the BNNT.
“This time we used iron instead of gold,” Yap adds, explaining that gold’s melting temperature was low for the process his team used. “And when we tested the material, the electrons distributed uniformly across the whole surface of the nanotubes.”
That means that instead of having a line of stepping stones, there are many different paths across the river, and an electron will jump to the nearest one. For future use in wearable electronics, the multiplicity of paths ensures electricity is moving from one riverbank to the next, one way or another. Using scanning tunneling microscopy inside a transmission electron microscope (STM-TEM), the team successfully bent the iron dot-coated BNNT while monitoring the electron flows. The electronic behaviors remain the same even when the BNNT was bent all the way up to 75 degrees.
Yap says that this experiment is a proof of concept. While the iron BNNT material shows promise, it’s not a full transistor yet, capable of modulating electron movement. Right now, it’s called a flexible tunneling channel.
“Next, we’ll put the BNNT and iron onto a bendable plastic substrate,” Yap says. “Then we’ll bend this substrate and watch where the electrons go.”
This experimental work is complemented by computer simulations by John Jaszczak, professor of physics, and Paul Bergstrom, professor of electrical and computer engineering.
Which route the electricity takes is hard to track, which will be the main challenge for the next experiment. But one direction is certain, Yap’s research is headed down a path to change the basic level of electronics and make wearable tech more adaptable.
Michigan Technological University (www.mtu.edu) is a leading public research university developing new technologies and preparing students to create the future for a prosperous and sustainable world. Michigan Tech offers more than 120 undergraduate and graduate degree programs in engineering; forest resources; computing; technology; business; economics; natural, physical and environmental sciences; arts; humanities; and social sciences.
01 Oct 2015
Using nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.
Based on multiwall carbon nanotubes and tiny rectifiers fabricated onto them, the optical rectennas could provide a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity — and ultimately for a new way to efficiently capture solar energy.
In the new devices, developed by engineers at the Georgia Institute of Technology, the carbon nanotubes act as antennas to capture light from the sun or other sources. As the waves of light hit the nanotube antennas, they create an oscillating charge that moves through rectifier devices attached to them. The rectifiers switch on and off at record high petahertz speeds, creating a small direct current.
Billions of rectennas in an array can produce significant current, though the efficiency of the devices demonstrated so far remains below one percent. The researchers hope to boost that output through optimization techniques, and believe that a rectenna with commercial potential may be available within a year.
“We could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way” said Baratunde Cola, an associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. “As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture.”
The research, supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center and the Army Research Office (ARO), is scheduled to be reported September 28 in the journal Nature Nanotechnology.
Developed in the 1960s and 1970s, rectennas have operated at wavelengths as short as ten microns, but for more than 40 years researchers have been attempting to make devices at optical wavelengths. There were many challenges: making the antennas small enough to couple optical wavelengths, and fabricating a matching rectifier diode small enough and able to operate fast enough to capture the electromagnetic wave oscillations. But the potential of high efficiency and low cost kept scientists working on the technology.
“The physics and the scientific concepts have been out there,” said Cola. “Now was the perfect time to try some new things and make a device work, thanks to advances in fabrication technology.”
Using metallic multiwall carbon nanotubes and nanoscale fabrication techniques, Cola and collaborators Asha Sharma, Virendra Singh and Thomas Bougher constructed devices that utilize the wave nature of light rather than its particle nature. They also used a long series of tests — and more than a thousand devices — to verify measurements of both current and voltage to confirm the existence of rectenna functions that had been predicted theoretically. The devices operated at a range of temperatures from 5 to 77 degrees Celsius.
Fabricating the rectennas begins with growing forests of vertically-aligned carbon nanotubes on a conductive substrate. Using atomic layer chemical vapor deposition, the nanotubes are coated with an aluminum oxide material to insulate them. Finally, physical vapor deposition is used to deposit optically-transparent thin layers of calcium then aluminum metals atop the nanotube forest. The difference of work functions between the nanotubes and the calcium provides a potential of about two electron volts, enough to drive electrons out of the carbon nanotube antennas when they are excited by light.
In operation, oscillating waves of light pass through the transparent calcium-aluminum electrode and interact with the nanotubes. The metal-insulator-metal junctions at the nanotube tips serve as rectifiers switching on and off at femtosecond intervals, allowing electrons generated by the antenna to flow one way into the top electrode. Ultra-low capacitance, on the order of a few attofarads, enables the 10-nanometer diameter diode to operate at these exceptional frequencies.
“A rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode,” Cola explained. “The closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode — which is the structure we made.”
The rectennas fabricated by Cola’s group are grown on rigid substrates, but the goal is to grow them on a foil or other material that would produce flexible solar cells or photodetectors.
Cola sees the rectennas built so far as simple proof of principle. He has ideas for how to improve the efficiency by changing the materials, opening the carbon nanotubes to allow multiple conduction channels, and reducing resistance in the structures.
“We think we can reduce the resistance by several orders of magnitude just by improving the fabrication of our device structures,” he said. “Based on what others have done and what the theory is showing us, I believe that these devices could get to greater than 40 percent efficiency.”
- Asha Sharma, Virendra Singh, Thomas L. Bougher, Baratunde A. Cola. A carbon nanotube optical rectenna. Nature Nanotechnology, 2015; DOI: 10.1038/nnano.2015.220
25 Jul 2015
Engineered carbon nanotube membranes may help solve our growing demand for desalination.
Of course, you can’t just drink a glass of water straight from the sea. But it is possible to use water from the ocean once the salts are removed. In fact, desalination plants already provide much of the water used by people in many parts of the world, especially in Israel, Saudi Arabia, and Australia.
Climate change is only increasing the demand for desalinated water as greater evaporation and rising seas further limit freshwater supplies for a growing world population. But desalinating water today comes at a very high cost in terms of energy, which means more greenhouse gases and more global warming.
Researchers from the University of Malaya’s Nanotechnology and Catalysis Research Center in Kuala Lumpur in Malaysia say in the journal Desalination that carbon nanotube (CNT) membranes have a bright future in helping the world’s population meet the need for purified water from the sea.
“Currently, about 400 million people are using desalinated water and it has been projected that by 2025, 14 percent of the global population will be forced to use sea water,” said Md. Eaqub Ali, corresponding author of the paper presenting the current problems and future challenges in water treatments.
Existing desalination plants rely on reverse osmosis, vacuum distillation, or a combination of the two, he explained. But those methods are energy intensive, and that’s where the potential for carbon nanotube membranes comes in.
Carbon nanotubes are teeny tiny hexagonal tubes, made by rolling sheets of graphene, said Rasel Das, first author of the paper. They require little energy and can be designed to specifically reject or remove not only salt, but also common pollutants.
“The hollow pores of the CNTs are extremely, extremely tiny,” Ali said. “However, because of their amazing chemical and physical properties, they allow frictionless passes of water through the pores, but reject most salts, ions, and pollutants, giving us purified water, probably in its best form.” An array of carbon nanotubes (red) forming a membrane that is highly permeable to water (blue surface), but not sodium (yellow) and chloride (green) ions.
That frictionless property is what gives CNTs the potential to purify water with so little energy. And carbon nanotube membranes come with other perks, Das added, including self-cleaning properties.
“What makes CNTs special is that they have cytotoxic properties,” he said. That means that the membranes naturally kill microbes that might otherwise foul up their surfaces. As a result, carbon nanotube membranes have the potential to last longer much longer than those in use today.
There are hurdles yet to overcome, co-author of the paper Sharifah Bee Abd Hamid said. The CNT membranes themselves are now costly to produce, especially for large-scale uses. Research is also needed to produce the membranes with pores of a more uniform distribution and size.
“Most progress in desalination research is focused on demonstrating the capability of CNT membranes at a small scale,” she said.
For larger scale operations, work is needed to produce CNT membranes on thin films or fiber cloth composites. Getting CNT membranes ready for use will require effort on material design, operational requirements, and more.
If someday, these membranes can be put to use in water-filtering pitchers or bottles, “to directly treat salty water at point of use,” Hamid says, “it is a dream come true for many.”
Did you know?
Only 2 percent of the water on Earth comes in the form of freshwater. Of that 2 percent, 70 percent is snow and ice, 30 percent is hidden underground, and less than 0.5 percent is found in surface waters including lakes, ponds and rivers.
07 Jul 2015
Nearly 800 million people worldwide don’t have access to safe drinking water, and some 2.5 billion people live in precariously unsanitary conditions, according to the Centers for Disease Control and Prevention.
Together, unsafe drinking water and the inadequate supply of water for hygiene purposes contribute to almost 90% of all deaths from diarrheal diseases — and effective water sanitation interventions are still challenging scientists and engineers.
A new study published in Nature Nanotechnology proposes a novel nanotechnology-based strategy to improve water filtration. The research project involves the minute vibrations of carbon nanotubes called “phonons,” which greatly enhance the diffusion of water through sanitation filters. The project was the joint effort of a Tsinghua University-Tel Aviv University research team and was led by Prof. Quanshui Zheng of the Tsinghua Center for Nano and Micro Mechanics and Prof. Michael Urbakh of the TAU School of Chemistry, both of the TAU-Tsinghua XIN Center, in collaboration with Prof. Francois Grey of the University of Geneva.
Shake, rattle, and roll
“We’ve discovered that very small vibrations help materials, whether wet or dry, slide more smoothly past each other,” said Prof. Urbakh. “Through phonon oscillations — vibrations of water-carrying nanotubes — water transport can be enhanced, and sanitation and desalination improved. Water filtration systems require a lot of energy due to friction at the nano-level. With these oscillations, however, we witnessed three times the efficiency of water transport, and, of course, a great deal of energy saved.”
The research team managed to demonstrate how, under the right conditions, such vibrations produce a 300% improvement in the rate of water diffusion by using computers to simulate the flow of water molecules flowing through nanotubes. The results have important implications for desalination processes and energy conservation, e.g. improving the energy efficiency for desalination using reverse osmosis membranes with pores at the nanoscale level, or energy conservation, e.g. membranes with boron nitride nanotubes.
Crowdsourcing the solution
The project, initiated by IBM’s World Community Grid, was an experiment in crowdsourced computing — carried out by over 150,000 volunteers who contributed their own computing power to the research.
“Our project won the privilege of using IBM’s world community grid, an open platform of users from all around the world, to run our program and obtain precise results,” said Prof. Urbakh. “This was the first project of this kind in Israel, and we could never have managed with just four students in the lab. We would have required the equivalent of nearly 40,000 years of processing power on a single computer. Instead we had the benefit of some 150,000 computing volunteers from all around the world, who downloaded and ran the project on their laptops and desktop computers.
“Crowdsourced computing is playing an increasingly major role in scientific breakthroughs,” Prof. Urbakh continued. “As our research shows, the range of questions that can benefit from public participation is growing all the time.”
The computer simulations were designed by Ming Ma, who graduated from Tsinghua University and is doing his postdoctoral research in Prof. Urbakh’s group at TAU. Ming catalyzed the international collaboration. “The students from Tsinghua are remarkable. The project represents the very positive cooperation between the two universities, which is taking place at XIN and because of XIN,” said Prof. Urbakh.
Other partners in this international project include researchers at the London Centre for Nanotechnology of University College London; the University of Geneva; the University of Sydney and Monash University in Australia; and the Xi’an Jiaotong University in China. The researchers are currently in discussions with companies interested in harnessing the oscillation know-how for various commercial projects.