Scientists at Ulsan National Institute of Science and Technology (UNIST) in Korea and Karlsruhe Institute of Technology in Germany have developed a new energy conversion and storage system using seawater for the cathode in a fuel cell.
We’ve seen that sodium can serve as an alternative to lithium in rechargeable batteries. That’s because the reversible storage mechanisms for sodium ions are very similar. Sodium is also attracting attention as a replacement for lithium in alkali-metal-air batteries.
The Korean-German team’s paper has been published in the journal NPG Asia Materials as open access, available to everyone. The new system is described as an intermediate between a battery and a fuel cell, and is accordingly referred to as a hybrid fuel cell.
The circulating seawater in the open-cathode system results in a continuous supply of sodium ions. The circumstances allow the system to operate with superior cycling stability allowing the application of various alternative anodes to sodium metal by compensating for irreversible charge losses.
Hard carbon and tin-carbon nanocomposite electrodes were successfully applied as anode materials, yielding highly stable cycling performance and reversible capacities exceeding an initially impressive 110 mAh g−1 with hard carbon and 300 mAh g−1 with tin-carbon electrodes.
Both lithium and sodium batteries are promising systems that provide very high theoretical energy densities. But the use of pure alkali metals such as lithium and sodium for the anodes creates safety and cost issues associated with their reactivity and the expense of the required dry-assembly process.
The authors of the paper about the new hybrid fuel cell note:
We have designed a novel energy conversion and storage system using seawater, or more precisely, the NaCl dissolved in seawater, as a sodium source. The use of naturally-abundant seawater as a sodium source renders unnecessary any additional processing and allows for a substantial reduction of the manufacturing cost for energy storage and conversion devices. The herein-reported device is an intermediate system between batteries and fuel cells and is thus referred to as a hybrid fuel cell.
Differing from conventional batteries, which comprise alkali-metal-containing intercalation or insertion materials as electrodes in a closed system, this novel concept gains its active material from seawater, which is circulated in the open cathode. Such an abundant supply of active material (sodium dissolved in seawater) enables the use of various alloying-anode materials, such as silicon, tin or germanium, overcoming the limitation introduced by the irreversibility of the first and, to a lesser extent, subsequent alloying processes.
. . . circulating seawater in an open-system electrode corresponds to a continuous supply of sodium ions, which gives this system superior cycling stability and allows the application of various anodes by compensating for irreversible charge losses. The negative electrode of this novel hybrid battery/fuel cell system is, instead, closed and separated from the open-seawater positive electrode by a NASICON solid electrolyte. The negative electrode might be composed of sodium metal, in metal-seawater configuration, or a sodium-ion host (e.g., an alloying material), in full sodium-ion configuration.
For the experiments discussed in the paper the team fabricated the negative electrode from an 80:10:10 (wt.%) mixture of hard carbon or tin-carbon, SuperP carbon black as a conductive additive, and poly(vinylidene fluoride) as a binder. Seawater containing sodium chloride was used as the positive electrode.
During charging, the sodium+ ions present at the cathode diffuse through s NASICON electrolyte and transfer to the negative electrode, where the release of gaseous chlorine2 is released. Upon discharge, the oxygen dissolved in seawater is reduced, resulting in the formation of NaOH in the presence of water and sodium ions. The participation of oxygen in the reduction reaction boosts the theoretical discharge potential to 3.11 V from 1.88 V in de-aerated water.
With hard carbon as the sodium-ion negative-electrode, the discharge capacity (sodium uptake) was 114.4 mAh g−1, whereas the irreversible capacity amounted to 60 mAh g−1. This latter value decreased with increasing cycle number, although the reversible capacity slightly decreased. Such an electrochemical performance is typical of hard carbons, the authors said, indicating that seawater can serve as the source of sodium ions as well as conventional cathode materials in sodium-ion batteries.
Anodes based on the high-capacity Sn-C nanocomposite showed a first-cycle irreversible capacity of ~200 mAh g−1, and the reversible capacity was ~300 mAh g−1. The team attributed the “rather high irreversible capacity” is to electrolyte decomposition at the particle surface, resulting in the formation of a solid-electrolyte interphase, as well as structural rearrangement occurring upon the first sodiation within the micron-sized composite particles. For subsequent cycles, the reversible capacity increased to >300 mAh g−1 at the 5th cycle, accompanied by a continuously decreasing irreversible capacity (~90 mAh g−1 at the 5th cycle).
In the study the authors explain, “Generally, the performance of both the anode materials (hard carbon and Sn-C nanocomposite) in combination with the seawater cathode is very stable upon continuous cycling, showing a remarkably low capacity fading of only 0.02% and 0% after 30 cycles for the hard carbon and Sn-C anode, respectively). These results again highlight the great advantage of an almost infinite supply of sodium ions by employing the open-system seawater cathode.”
“Hybrid fuel cells using seawater as the positive electrode show great promise as next-generation energy conversion and storage systems that allow both high energy density and low environmental impact at a low cost. In addition, this system can be easily scaled up. It appears noteworthy that the gaseous Cl2 released upon charge might be trapped somehow and later utilized for other applications. Indeed, the production of gaseous Cl2 might provide another great advantage of this technology, adding some value to this new device,” they said.
This is a pretty big idea that actually works from the first lab bench prototype. There is a lot of potential here. For now the impressive thing is the intuitiveness of the research team. These resources have been constantly at our disposal and only now have been noticed and experiments begun to make use of them.
Researchers from the Universidad Politécnica de Madrid and the Universidad Miguel Hernández of Elche have found the way to increase biomass production by using sewage sludge as energy crop fertilizers. The idea’s press release is getting international attention.
Its not a new idea exactly. The City of Milwaukee Wisconsin has been the source of “Milorganite“, one of the oldest branded fertilizers on the market today, since 1926. Milorganite is the trademark of a biosolids fertilizer produced by the Milwaukee Metropolitan Sewerage District. Get it at a Home Depot near you. It is composed of heat-dried microbes that have digested the organic matter in wastewater. The Milorganite program is one of the world’s oldest and largest recycling efforts.
The Spaniard’s idea is a little different, though. They have carried out joint research work to determine the fertilization effects with sewage sludge compost. That’s quite a different thing. The effects were tested on cynara productivity over three years. The results showed that the usage of this fertilizer has clear positive effects since the biomass production and the oilseeds increased up to 40% and 68% respectively – a substantial increase of energy crop production. The team’s paper has been published in The Journal of Cleaner Production.
The usage of sewage sludge to fertilize energy crops could be an opportunity to reuse the fertility elements since these farm products are not intended for the human food industry.
Recovery and reuse of metropolitan sewage is rife with frightening problems. Sewage can contain horrific microbes like polio, cholera and a broad array of other scary things like heavy metals. Its not exactly cheap to clean it up enough for your garden. The clever folks in Milwaukee have done just that by going one more step and harvesting the microbes without the chemicals and diseases going along too.
In Spain energy crops, such as the cynara ones (Cynara cardunculus L.), are crops specifically intended for the production of renewable energy which is biomass energy or bioenergy. It is an herbaceous perennial crop adapted to the Mediterranean climate with annual growth cycles. This will allow the same crop can be harvested every year.
There producers can obtain two types of biomass from cynara crops every year. One is the lignocellulosic biomass which is useful for a solid biofuel in producing thermal energy. The other type of biomass is an oilseed that by extracting the oil can be used for advanced biofuels such as biodiesel production.
Sewage sludge is a residual and organic product rich in nutrients that is increasingly generated as a consequence of the treatment of growing amounts of urban wastewater. Because of its origin and composition, the usage of sewage sludge in agriculture is regulated in order to avoid risks of contamination of food products and the environment.
The fertilization of energy crops is essential in the management of the crop in order to not deplete soils and to make them more productive. Using sewage sludge and its derivatives to fertilize crops, instead of mineral fertilizers, does not involve any direct risk because these energy crops are not intended for food industry. The Spaniards believe study is needed to quantify the effects when using this fertilizer on the performance of energy crops.
This joint research of UPM, with Dr. Lag-Brotons, and researchers from UMH, shows the effects of using sewage sludge compost as fertilizer of energy crop of cynara for three consecutive years. Researchers used four levels of fertilization with composted sludge and they determined the performance in lignocellulosic biomass, oilseeds, oil and total energy.
The results showed that deep fertilization with sewage sludge compost has clear positive effects on crop productivity. Using sewage sludge compost has also achieved synergies from diverse areas of interest such as soil protection, the maintenance of its fertilization, the usage of residual products from the management of urban wastewater, and biomass production for energy purposes.
All well and good, if a little vague. So folks, “What does it cost to do it this way?”
There is a huge value of natural fertilizer being generated every day across the developed world that can be found at the water treatment facilities of every town and city. People are at the top of the food chain, or more adroitly, the carbon cycle. It seems quite weird that the planet’s top critter’s waste is the last one to be regularly returned to the natural order of things. Lazy people.
Think about it the next time you consider pouring chemicals down the drain.
November 19, 2014 | Leave a Comment
A team of researchers from Vanderbilt University and Oak Ridge National Laboratory (ORNL) has reported a discovery of an entirely new form of crystalline order that simultaneously exhibits both crystal and polycrystalline properties. The newly found crystalline order is being described as “interlaced crystals”. The interlaced crystal arrangement has properties that make it ideal for thermoelectric applications that turn heat into electricity.
The discovery of materials with improved thermoelectric efficiency could increase the efficiency of electrical power generation, improve automobile mileage and reduce the cost of air conditioning.
The story begins with the ream describing finding this unusual arrangement of atoms while studying nanoparticles made from the semiconductor copper-indium sulfide (CIS), which is being actively studied for use in solar cells.
The press release tells the story well:
“We discovered this new form while studying nanoparticles,” said Sokrates Pantelides, University Distinguished Professor of Physics and Engineering at Vanderbilt, who coordinated the study. “It most likely exists in thin films or bulk samples, but it has apparently gone unnoticed.”
In crystalline materials, atoms are arranged in periodic arrays of points, a mathematical abstraction called a Bravais lattice. There are 14 different types of Bravais lattices in three dimensions. The same atom or group of atoms sits at each lattice point. The simplest and most symmetric is the “simple cubic” lattice. Square floor tiles provide a two-dimensional example. The corners of the tiles create a regular, repeating lattice pattern. A three-dimensional version is the face centered cubic (FCC), which has points both on the corners and at the centers of the faces of a cube.
A number of minerals have an FCC lattice. Imagine shrinking an FCC lattice, down to the atomic scale and placing different atoms at each lattice point. When you have more than one atom at each point, each type of atom forms its own sub-lattice. For example, if you put a pair of carbon atoms at each point (forming two FCC sub-lattices), you get diamond. If you put a pair of sodium and chlorine atoms at each lattice point, they form sodium and chlorine sub-lattices and you get salt.
CIS is a bit more complicated. You can think of the sulfur atoms occupying one FCC sub-lattice while the copper and indium atoms share a second sub-lattice. Each copper or indium atom is surrounded by four nearest-neighbor sulfur atoms while each sulfur is surrounded by two copper and two indium nearest-neighbors.
Bulk CIS generally has a cubic structure. But, when Vanderbilt Assistant Professor of Chemistry Janet Macdonald and her post-doctoral student Emil Hernandez-Pagan grew nanocrystals of CIS to explore their properties for solar light harvesting, they found that the tiny crystals had a hexagonal lattice structure, with the sulfur atoms occupying one sub-lattice and the copper and indium atoms sharing another.
“In CIS, the sulfur atoms make these perfectly packed layers and the copper and Indium ions lie in between, like jam in a sandwich. Emil was making nanoparticles of this material in the lab, but we didn’t know if the copper and indium were ordered or just randomly distributed in the ‘jam’ layers,” said Macdonald. “This was important because disordered structures generally have poor electrical properties.”
Because of the small size of nanoparticles, X-ray diffraction, the normal method for determining crystal structure, could not tell whether the copper and indium atoms were ordered in some fashion.
Vanderbilt Research Assistant Professor Xiao Shen in Pantelides’ group performed theoretical calculations to determine whether an ordered or disordered distribution of the copper and indium atoms was preferred and concluded that several different ordered structures were preferred over a disordered structure and all the ordered structures had an equal likelihood of occurring.
The scientists didn’t have a clear idea about how these different ordered structures could coexist until Wigner Fellow Wu Zhou at ORNL successfully obtained detailed atomic-scale images of the nanoparticles. His images clearly showed that, while all atoms occupy the points of a perfect hexagonal Bravais lattice, the copper and indium atoms form a series of distinct domains where the copper and indium atoms are arranged differently. The boundaries between distinct copper-indium arrangements are similar to grain boundaries in polycrystalline solids, but both Shen’s calculations and the images revealed that the underlying hexagonal lattice is totally undisturbed.
When the researchers analyzed the images even more closely, “then things got even more interesting,” Macdonald said. “We discovered it was really hard to decide exactly where the edges were between the areas of different ordering. Usually it is really clear because normally when you have polycrystalline samples, there is strain at the edges between the different areas. So it was very strange that there seemed to be no strain or breaks at the edges. The underlying lattice was completely unperturbed by these different regions of copper/indium ordering. It was really quite amazing that despite all these little crystallites, the whole crystal lattice is completely happy and doesn’t need to shift or twist or break to accommodate them.”
The interlaced crystal structure may be just what is needed to optimize thermoelectric applications for energy harvesting for power generation or drawing off heat for cooling. Thermoelectric devices need a material that is an excellent electrical conductor and simultaneously a poor conductor of heat. So far the problem has been that materials like metals that are good electrical conductors also tend to be good heat conductors and vice versa. Inside the crystal structure defects and grain boundaries that retard heat flow also reduce electrical conductivity.
Pantelides wound up the press release saying, “We haven’t tested this yet, but we are confident that these materials have high electrical conductivity and low thermal conductivity. . . Just what you need for thermoelectrics. The field is now wide open for scientists who can fabricate thin films and make thermoelectric measurements.”
Exactly. Thermoelectric is a field with immense promise for energy production and conservation. Its a promise with very little practical result so far. Lets hope this is the big break.
Another note, this team needs congratulated for attention to the work such that the anomaly in the work became a huge opportunity. Serindipity? Perhaps, but mental discipline had an important role and for that everyone should take note and try to emulate the skill and concentration that found something new that had been thought to be a closed field for 175 years. Its been a very long time since the conclusion was made that crystalline materials are organized into fourteen different basic lattice structures.
November 18, 2014 | Leave a Comment
Northwestern University scientists are working to isolate atomically thin layers of molybdenum disulfide. Thinned down molybdenum disulfide has immediate and obvious applications in electronics, optoelectronics, solar cells, and catalysis.
Atom thick sheets of material got researchers rolling when graphene was first produced in the lab in 2004. Literally thousands of laboratories began developing graphene products worldwide. The graphene attributes amazed researchers with its lightweight and ultra-strong properties. Time and research have added conductivity and other attributes.
Now a decade on scientists are now searching for other materials that have the same level of potential. Molybdenum disulfide is at the top of the list and may have even more potential.
Mark Hersam, the Bette and Neison Harris Chair in Teaching Excellence at McCormick, who is a graphene expert said, “We continue to work with graphene, and there are some applications where it works very well. But it’s not the answer to all the world’s problems.”
Molybdenum disulfide (MoS2) is part of a family of materials called transition metal dichalcogenides and is emerging as a frontrunner material for exploration in Hersam’s lab.
Like graphene, MoS2 can be exfoliated into atomically thin sheets. As it thins to the atomic limit, it becomes fluorescent, making it useful for optoelectronics, such as light-emitting diodes, or light-absorbing devices, such as solar cells. MoS2 is also a true semiconductor, making it an excellent candidate for electronics.
MoS2 has been in use a long time, historically has been used as a dry lubricant and in catalysis to remove sulfur from crude oil, which prevents acid rain.
Hersam’s challenge was to find a way to isolate atomically thin sheets of MoS2 material at a larger scale. For the past six years, his lab has developed methods for exfoliating thin layers of graphene from graphite, using solution-based methods at large scale.
“You would think it would be easy to do the same thing for molybdenum disulfide. But the problem is that while the exfoliation is similar to graphene, the separation is considerably more challenging,” he said.
Hersam’s research is described in the paper “Thickness sorting of two-dimensional transition metal dichalcogenides via copolymer-assisted gradient ultracentrifugation,” which was published in the Nov. 13 issue of Nature Communications.
To sort graphene layers, Hersam used centrifugal force to separate materials by density. To do this, he and his group added the material to a centrifuge tube along with a gradient of water-based solution. Upon centrifugation, the denser species move toward the bottom, creating layers of densities within the centrifuge tube. Graphene sorts into single layer sheets toward the top, then bilayer sheets, trilayer, and so on. Because graphene has a relatively low density, it easily sorts compared to higher density materials.
“If I use the exact same process with molybdenum disulfide, its higher density will cause it to crash out,” Hersam said. “It exceeds the maximum density of the gradient, which required an innovative solution.”
Hersam needed to take the inherently dense material and effectively reduce its density without changing the material itself. He realized that this goal could be achieved by tuning the density of the molecules used to disperse MoS2. In particular, the use of bulkier polymer dispersants allowed the effective density of MoS2 to be reduced into the range of the density gradient. In this manner, the sheets of MoS2 floated at layered positions instead of collecting as the bottom of the centrifuge tube. This technique works not just for MoS2, but for other materials in the transition metal dichalcogenides family.
“Now we can isolate single layer, bilayer, or trilayer transition metal dichalcogenides in a scalable manner,” Hersam said. “This process will allow us to explore their utility in large-scale applications, such as electronics, optoelectronics, catalysis, and solar cells.”
Molybdenum disulfide has always had a bright future, its amazing stuff with very attractive qualities at the micro scale. At the nano scale, catalysis, electronics and the soon to take off optoelectronics field, MoS2 looks like an important material for reducing the energy used to accomplish more work at lower cost.
November 13, 2014 | 2 Comments
The University of Colorado Boulder research is a first-of-its-kind analysis. It is also not a particular surprise to people familiar with the industry. The results will be a disappointment to those opposed to oil and gas well fracturing.
Fracking fluid is largely composed of water and sand, but oil and gas companies also add a variety of other chemicals, including anti-bacterial agents, corrosion inhibitors and surfactants. Surfactants reduce the surface tension between water and oil, allowing for more oil to be extracted from porous rock underground.
The fluids are not so very different from washing dishes with antibacterial soap.
In a new study published in the journal Analytical Chemistry, the research team identified the surfactants found in fracking fluid samples from Colorado, Louisiana, Nevada, Pennsylvania and Texas. The results showed that the chemicals found in the fluid samples were also commonly found in everyday products, from toothpaste to laxatives to detergent to ice cream.
Michael Thurman, lead author of the paper and a co-founder of the Laboratory for Environmental Mass Spectrometry in CU-Boulder’s College of Engineering and Applied Science said, “This is the first published paper that identifies some of the organic fracking chemicals going down the well that companies use. We found chemicals in the samples we were running that most of us are putting down our drains at home.”
Imma Ferrer, chief scientist at the mass spectrometry laboratory and co-author of the paper said, “Our unique instrumentation with accurate mass and intimate knowledge of ion chemistry was used to identify these chemicals.” The mass spectrometry laboratory is sponsored by Agilent Technologies, Inc., which provides state-of-the art instrumentation and support.
The fluid samples analyzed for the study were provided through partnerships with Colorado State University and colleagues at CU-Boulder.
Hydraulic fracturing, or “fracking,” is a technique used to increase the amount of oil and gas that can be extracted from the ground by forcing fluid down the well. Fracking has allowed for an explosion of oil and gas operations across the country. In the U.S. the number of natural gas wells has increased by 200,000 in the last two decades, according to the U.S. Energy Information Administration.
Among the concerns raised by the fracking boom is that the chemicals used in the fracking fluid might contaminate ground and surface water supplies. But determining the risk of contamination, or proving that any contamination has occurred in the past, has been difficult because oil and gas companies have been reluctant to share exactly what’s in their proprietary fluid mixtures, citing stiff competition within the industry.
Recent state and federal regulations require companies to disclose what is being used in their fracking fluids, but the resulting lists typically use broad chemical categories to describe the actual ingredients.
The results of the new study are important not only because they give a picture of the possible toxicity of the fluid but because a detailed list of the ingredients can be used as a “fingerprint” to trace whether suspected contamination of water supplies actually originated from a fracking operation.
The authors caution that their results may not be applicable to all wells. Individual well operators use unique fracking fluid mixtures that may be modified depending on the underlying geology. Ferrer and Thurman are now working to analyze more water samples collected from other wells as part of a larger study at CU-Boulder exploring the impacts of natural gas development.
Thurman notes that there are other concerns about fracking – including air pollution, the antimicrobial biocides used in fracking fluids, wastewater disposal triggering earthquakes and the large amount of water used – that are important to investigate and ameliorate. But water pollution from surfactants in fracking fluid may not be as big a concern as previously thought.
“What we have learned in this piece of work is that the really toxic surfactants aren’t being used in the wells we have tested,” he said.
The news media and entertainment industries would have us believe the oil and gas industry is populated with characters like the famous nefarious fictional JR Ewing of the TV show Dallas.
Here in the U.S. the oil and gas business is run by 8 million or so folks like you and me trying to earn a living, make some money and provide products that we will choose to use.