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Fuel cell electric vehicles have a long way to go before they can compete with their battery EV cousins, and energy storage is a key sticking point when the fuel is hydrogen. Hydrogen is light, plentiful, and fabulously energy dense, but energy storage in a personal mobility unit racing down a crowded highway is a different kind of chicken. Safety, cost, and performance are critical sticking points, and a research team at Lawrence Berkeley Laboratory is on to a solution for at least one of those.

hydrogen energy storage with graphene

Energy Storage Challenges For Hydrogen Fuel Cell EVs

The US Energy Department’s 2015 annual report provides a birds-eye view of the array of energy storage solutions that are emerging for hydrogen fuel cells, including advancements in hydrogen tank technology as well as solids-based storage.

Despite the progress, according to the Energy Department, challenges still remain for stationary and portable fuel cells in terms of raising the energy storage density, and there are “significant challenges” for fuel cell EVs. The problem is this:

Hydrogen has the highest energy per mass of any fuel; however, its low ambient temperature density results in a low energy per unit volume, therefore requiring the development of advanced storage methods that have potential for higher energy density.

The Energy Department has set a goal of 2020 for achieving verifiable hydrogen storage systems for light duty fuel cell EVs that meet the driving public’s thirst for range, comfort, refueling convenience, and performance. Here are the targets:

1.8 kWh/kg system (5.5 wt.% hydrogen)

1.3 kWh/L system (0.040 kg hydrogen/L)

$10/kWh ($333/kg stored hydrogen capacity)

Fuel cell EVs are already leaking into the transportation scene, particularly in California, Japan, and the European Union, notably including Wales.

However, the Energy Department is already looking beyond the current state of on-road technology to meet its 2020 goal. According to the agency, the 300-mile range is being met by using compressed gas, high pressure energy storage technology, and the problem is that competing technology on the market today — primarily gasmobiles and hybrids — already exceeds that range.

To compete for consumers on the open market, the agency is pursuing a near-term goal of improving compressed gas storage, primarily by deploying fiber reinforced composites that enable 700 bar pressure.

The long term goal consists of two pathways. One is to improve “cold” compressed gas energy storage technology, and the other is to go a different route altogether and store hydrogen within materials such as sorbents, chemical hydrogen storage materials, and metal hydrides.

The Berkeley Lab Energy Storage Solution

Where were we? Oh right, Berkeley Lab. Berkeley Lab has been tackling the metal hydride pathway.

Metal hydrides are compounds that consist of a transition metal bonded to hydrogen. They are believed to be the most “technologically relevant” class of materials for storing hydrogen, partly due to the broad range of applications.

That’s the theory. The problem is that when it comes to real world performance, metal hydrides are highly sensitive to contamination and they degrade somewhat rapidly unless properly shielded.

The Berkeley Lab energy storage solution consists of a graphene “filter” encasing nanocrystals of magnesium. With the addition of the graphene layer, the magnesium crystals act as a sort of sponge for absorbing hydrogen, providing both safety and compactness without causing performance issues:

The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for hydrogen storage.

Berkeley Lab has provided this photo to show off how stable the crystals are when exposed to air (for scale, the bottle cap is about the size of a thumbnail):

graphene hydrogen energy storage

At one atom thick (yes, one atom), graphene is known to be an incredibly finicky material to work with. It is extremely difficult to synthesize it without defects, but that’s not a problem for this energy storage solution. The defects are actually desirable in this case. The tiny gaps enable molecules of hydrogen gas to wriggle through, but oxygen, water, and other contaminants are too large to penetrate the shield.

The new energy formula also solves another key challenge for metal hydrides. They tend to take in and dispense hydrogen at a relatively slow pace, but the Berkeley Lab solution has sped up the intake-outflow cycle significantly. That effect is attributed to the nanoscale size of the graphene-shielded crystals, which provide a greater surface area.

Energy Department Gets The Last Word?

We’ve been having a lively debate about fuel cell electric EVs over here at CleanTechnica, so let’s hear from the Berkeley Lab team:

A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that hydrogen fuel cells can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.

However, the team also makes it clear that:

More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries…

Among other issues, the next step for a sustainable fuel cell EV future is to develop sustainable and renewable sources for hydrogen fuel. Currently the main source of hydrogen is natural gas, which puts fuel cell EVs in the same boat as battery EVs that draw electricity from a coal or natural gas-fired grid.

Super Oxide Battery id42324While lithium-ion batteries have transformed our everyday lives, researchers are currently trying to find new chemistries that could offer even better energy possibilities. One of these chemistries, lithium-air, could promise greater energy density but has certain drawbacks as well.
Now, thanks to research at the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory, one of those drawbacks may have been overcome (Nature, “A lithium–oxygen battery based on lithium superoxide”).
text
The lattice match between LiO2 and Ir3Li may be responsible for the LiO2 discharge product found for the Ir-rGO cathode material.
All previous work on lithium-air batteries showed the same phenomenon: the formation of lithium peroxide (Li2O2), a solid precipitate that clogged the pores of the electrode.
In a recent experiment, however, Argonne battery scientists Jun Lu, Larry Curtiss and Khalil Amine, along with American and Korean collaborators, were able to produce stable crystallized lithium superoxide (LiO2) instead of lithium peroxide during battery discharging. Unlike lithium peroxide, lithium superoxide can easily dissociate into lithium and oxygen, leading to high efficiency and good cycle life.
“This discovery really opens a pathway for the potential development of a new kind of battery,” Curtiss said. “Although a lot more research is needed, the cycle life of the battery is what we were looking for.”
The major advantage of a battery based on lithium superoxide, Curtiss and Amine explained, is that it allows, at least in theory, for the creation of a lithium-air battery that consists of what chemists call a “closed system.” Open systems require the consistent intake of extra oxygen from the environment, while closed systems do not — making them safer and more efficient.
“The stabilization of the superoxide phase could lead to developing a new closed battery system based on lithium superoxide, which has the potential of offering truly five times the energy density of lithium ion,” Amine said.
Curtiss and Lu attributed the growth of the lithium superoxide to the spacing of iridium atoms in the electrode used in the experiment. “It looks like iridium will serve as a good template for the growth of superoxide,” Curtiss said.
“However, this is just an intermediate step,” Lu added. “We have to learn how to design catalysts to understand exactly what’s involved in lithium-air batteries.”
Source: Argonne National Laboratory

2D Perovskite Berkeley Peidong-image-2Berkeley Lab Researchers Produce First Ultrathin Sheets of Perovskite Hybrids

To the growing list of two-dimensional semiconductors, such as graphene, boron nitride, and molybdenum disulfide, whose unique electronic properties make them potential successors to silicon in future devices, you can now add hybrid organic-inorganic perovskites. However, unlike the other contenders, which are covalent semiconductors, these 2D hybrid perovskites are ionic materials, which gives them special properties of their own.
Researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have successfully grown atomically thin 2D sheets of organic-inorganic hybrid perovskites from solution. The ultrathin sheets are of high quality, large in area, and square-shaped. They also exhibited efficient photoluminescence, color-tunability, and a unique structural relaxation not found in covalent semiconductor sheets.
“We believe this is the first example of 2D atomically thin nanostructures made from ionic materials,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division and world authority on nanostructures, who first came up with the idea for this research some 20 years ago. “The results of our study open up opportunities for fundamental research on the synthesis and characterization of atomically thin 2D hybrid perovskites and introduces a new family of 2D solution-processed semiconductors for nanoscale optoelectronic devices, such as field effect transistors and photodetectors.”

(From left) Peidong Yang, Letian Dou, Andrew Wong and Yi Yu successfully followed up on research first proposed by Yang in 1994.

Yang, who also holds appointments with the University of California (UC) Berkeley and is a co-director of the Kavli Energy NanoScience Institute (Kavli-ENSI), is the corresponding author of a paper describing this research in the journal Science. The paper is titled “Atomically thin two-dimensional organic-inorganic hybrid perovskites.” The lead authors are Letian Dou, Andrew Wong and Yi Yu, all members of Yang’s research group. Other authors are Minliang Lai, Nikolay Kornienko, Samuel Eaton, Anthony Fu, Connor Bischak, Jie Ma, Tina Ding, Naomi Ginsberg, Lin-Wang Wang and Paul Alivisatos.
Traditional perovskites are typically metal-oxide materials that display a wide range of fascinating electromagnetic properties, including ferroelectricity and piezoelectricity, superconductivity and colossal magnetoresistance. In the past couple of years, organic-inorganic hybrid perovskites have been solution-processed into thin films or bulk crystals for photovoltaic devices that have reached a 20-percent power conversion efficiency. Separating these hybrid materials into individual, free-standing 2D sheets through such techniques as spin-coating, chemical vapor deposition, and mechanical exfoliation has met with limited success.
In 1994, while a PhD student at Harvard University, Yang proposed a method for preparing 2D hybrid perovskite nanostructures and tuning their electronic properties but never acted upon it. This past year, while preparing to move his office, he came upon the proposal and passed it on to co-lead author Dou, a post-doctoral student in his research group. Dou, working mainly with the other lead authors Wong and Yu, used Yang’s proposal to synthesize free-standing 2D sheets of CH3NH3PbI3, a hybrid perovskite made from a blend of lead, bromine, nitrogen, carbon and hydrogen atoms.

Structural illustration of a single layer of a 2D hybrid perovskite (C4H9NH3)2PbBr4), an ionic material with different properties than 2D covalent semiconductors.

“Unlike exfoliation and chemical vapor deposition methods, which normally produce relatively thick perovskite plates, we were able to grow uniform square-shaped 2D crystals on a flat substrate with high yield and excellent reproducibility,” says Dou. “We characterized the structure and composition of individual 2D crystals using a variety of techniques and found they have a slightly shifted band-edge emission that could be attributed to structural relaxation. A preliminary photoluminescence study indicates a band-edge emission at 453 nanometers, which is red-shifted slightly as compared to bulk crystals. This suggests that color-tuning could be achieved in these 2D hybrid perovskites by changing sheet thickness as well as composition via the synthesis of related materials.”
The well-defined geometry of these square-shaped 2D crystals is the mark of high quality crystallinity, and their large size should facilitate their integration into future devices.
“With our technique, vertical and lateral heterostructures can also be achieved,” Yang says. “This opens up new possibilities for the design of materials/devices on an atomic/molecular scale with distinctive new properties.”
This research was supported by DOE’s Office of Science. The characterization work was carried out at the Molecular Foundry’s National Center for Electron Microscopy, and at beamline 7.3.3 of the Advanced Light Source. Both the Molecular Foundry and the Advanced Light Source are DOE Office of Science User Facilities hosted at Berkeley Lab.

Adam Weber and Jeffrey Urban at ALS SAXS/WAXS Beamline 7.3.3.New projects for hydrogen storage and fuel cell performance aim to bring down cost of fuel cell electric vehicles.

With commitments from leading car and stationary-power manufacturers to hydrogen and fuel cell technologies and the first ever fuel cell electric vehicle to go on sale later this year, interest is once again swelling in this carbon-free technology. Now, thanks to several new projects from the U.S. Department of Energy’s (DOE) Fuel Cell Technologies Office, scientists from Lawrence Berkeley National Laboratory (Berkeley Lab) will have an important role in accelerating innovation and commercialization of hydrogen and fuel cell technologies.

Berkeley Lab has been awarded $8 million for two new DOE research efforts, one to find new materials for hydrogen storage and another for optimizing fuel-cell performance and durability. In addition, Berkeley Lab is leading a range of other hydrogen and fuel cell research projects aimed at developing next-generation fuel cell and related energy-conversion technologies.

Adam Weber and Jeffrey Urban at ALS SAXS/WAXS Beamline 7.3.3.

“Berkeley Lab has had a strong fuel cell research program going back decades,” said scientist Adam Weber, who leads fuel cell research at Berkeley Lab. “With these new DOE consortiums, each national lab brings its core competences while synergistically leveraging each other. This way we’ll be able to push the state-of-the-art much faster and further than we could individually.”

Fuel cells are considered one of the most promising and fast-growing clean energy technologies. In 2014, about 50,000 fuel cell units were shipped worldwide, with a nearly 30 percent market growth every year since 2010. This year, Toyota’s Mirai will be the first fuel cell electric vehicle (FCEV) to be commercially available for sale in the U.S. Still, cost remains one of the biggest challenges to wider adoption.

The Fuel Cell—Consortium for Performance and Durability (FC-PAD) is led by Los Alamos National Laboratory and includes Argonne National Laboratory, Oak Ridge National Laboratory, and the National Renewable Energy Laboratory, with Weber serving as the consortium’s deputy director. Its goal is to improve and optimize polymer electrolyte membrane (PEM) fuel cells, which are used primarily for transportation, while reducing their cost. “If we can make individual cells more durable and perform better with less costly components or fewer of them, than you would drive down the cost of the vehicle,” Weber said.

Specifically one research focus of Weber’s work for FC-PAD will be trying to understand and optimize mass transport in the fuel cell, or the transport of reactants and products, such as hydrogen, oxygen, and water. Mass-transport issues can limit fuel-cell performance. “One of our core competences at Berkeley Lab is in mathematical modeling and advanced diagnostics, which we can use to study, explore, and describe the transport phenomena across length scales from the microstructural to macroscopic levels,” he said.

Like batteries, fuel cells use a chemical reaction to produce electricity. However fuel cells don’t need to be recharged; rather, they will produce electricity as long as fuel is supplied. In the case of a hydrogen fuel cell, hydrogen is the fuel, and it’s stored in a tank connected to the fuel cell.

Safe and cost-effective hydrogen storage is another challenge for FCEVs, one that the other DOE consortium, Hydrogen Materials—Advanced Research Consortium (HyMARC), seeks to address. HyMARC is led by Sandia National Laboratories and also includes Lawrence Livermore National Laboratory.

Jeff Urban, the HyMARC lead scientist for Berkeley Lab, noted the Lab’s strengths: “Berkeley Lab brings to the consortium a combination of innovation in H2 storage materials, surface and interface science, controlled nanoscale synthesis, world-class user facilities for characterizing nanoscale materials, and predictive materials genome capabilities.”

Researchers have two goals for hydrogen storage—greater storage density at lower pressure. Greater density will allow for greater vehicle driving range while lower pressure improves safety as well as efficiency.

Urban and his group have come up with novel ways to synthesize nanoscale metal hydrides to achieve extremely high hydrogen storage capacity. Yet the kinetics, or rate of chemical reactions, is one of the main challenges with this material. “HyMARC will allow us to further probe solid-solid interfaces in metal hydrides and evaluate microstructural engineering as a pathway to improved kinetics,” he said. “The unique combination of expertise spanning these consortia gives us a peerless network of close collaboration to surmount the fundamental scientific barriers underpinning some of these sticky challenges.”

Both of these consortiums are funded by DOE’s Fuel Cell Technologies Office, part of the Office of Energy Efficiency and Renewable Energy, and follow a similar model, where the core team consisting of the national labs will serve as a resource to industry and later also collaborate on innovative projects with universities and companies.

Another research focus is in catalysts, the subject of a collaboration between Berkeley Lab materials scientist Peidong Yang and scientists at Argonne National Laboratory. Last year they reported discovery of a new class of bimetallic nanoframe catalysts using platinum and nickel that are significantly more efficient and far less expensive than the best platinum catalysts used in today’s fuel cells.

Finally Berkeley Lab last month joined several other national labs as well as dozens of companies and other institutions in signing onto H2USA, a public-private partnership whose mission is “is to address hurdles to establishing hydrogen fueling infrastructure, enabling the large scale adoption of fuel cell electric vehicles.” Infrastructure is one of the critical challenges to wider hydrogen technology adoption, and one in which California has made a strong commitment.

“I’m very bullish on hydrogen. It’s clean and carbon-free, and it’s definitely a very integral part of the future energy economy,” Weber said. “Is it a very near-term drop-in replacement technology? No, I think it’s a little bit longer term, although we have commercial products like the Mirai available today. Like any new technology we have to go down the cost and manufacturing curves. As we bring in new ideas, concepts, and materials, I think we can easily bring down the cost.”

# # #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Updated:

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MIT: Analysis sees many Promising Pathways for Solar Photovoltaic Power

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Gaps in fracking-happeningx250Though applied since the 1940s, hydraulic fracturing boomed in the 1990s, according to The Geological Society of America. New technology allowed the practice to be applied to horizontal wells for extracting shale gas. Unprecedented growth followed. According to a 2014 report by FracTracker Alliance, over 1.1 million active oil and gas wells exist in the U.S.

“The rapid pace of shale gas development in the U.S. has naturally led to several gaps in knowledge about environmental impacts,” said Douglas Arent, executive director of the Joint Institute for Strategic Energy Analysis at the U.S. Dept. of Energy’s National Renewable Energy Laboratory.

Arent and colleagues recently published a paper in MRS Energy & Sustainability overviewing the developments of unconventional gas in the U.S., particularly focusing on trends in water and greenhouse gas emissions.

“If unconventional natural gas is produced and distributed responsibly, and incorporated into resilient energy systems with increasing levels of renewables, then gas can likely play a significant role in realizing a more sustainable energy future,” said Arent.

Gaps in fracking-happeningx250

Image: EPA

Water

With many U.S. states experiencing droughts—the west coast especially—water resources are stressed. Fresh water is a valuable resource. Even if one removes hydraulic fracturing from the equation, other domestic, agricultural and industrial water needs abound.

A recent Stanford Univ. study found that regardless how deep a well was, amounts of water used to frack were indistinguishable. The average volume used to frack, according to the study, was 2.4 million gallons.

“Groundwater depletion—a situation in which water is withdrawn from aquifers faster than it can be replenished—is occurring in many areas where there are shale plays,” Arent et al. write. “Depletion not only reduces the quantity of available water, it can also result in an overall deterioration of water quality.”

Water quality degradation can occur in a myriad of ways, from leaking wells and poor wastewater treatment practices, to spills and toxic element accumulation in soil. Clarity regarding the sources and mechanisms of contamination are needed, followed by an examination of effective practices to eliminate risks, according to the researchers.

“Currently, best management practices to mitigate (water) quantity and quality related risks have not been established by industry and stakeholder groups,” the researchers write. Further, no uniformity exists across the country. Individual states are responsible for regulations regarding well construction, and mitigating potential risks to water quality. Often separate state regulations don’t mesh due to each state’s geological makeup.

An “analysis will be critical to establishing those (best management practices) and government regulations, where needed, which will ensure that shale gas can be responsibly and sustainably produced,” write the researchers.

Greenhouse gas emissions
Natural gas production, compared to coal production, results in half the carbon emissions per unit of energy. The researchers contend natural gas can offer greenhouse gas mitigation benefits relative to coal, if methane emissions are small.

In 2014, the Environmental Protection Agency reported methane gas emissions from fractured natural gas wells decreased by 73% since 2011.

“Significant work is needed to measure and verify methane emissions across the full production, transportation and distribution value chain,” the researchers write. “If natural gas is to help mitigate climate change, it will do so primarily by displacing coal. However, in the long term, natural gas itself…will not significantly alter long-range climate projections.”

While natural gas, according to the researchers, will play an important role in the U.S.’s energy future, renewable energies or carbon capture and storage will be needed to meet carbon mitigation goals.

“More transparent and accessible data related to water use and emissions from shale gas development and use…are essential to providing a more complete understanding of all the pathways to a decarbonized energy future,” said Arent.

UC Berkley Solar Cells 090215 id41206By combining designer quantum dot light-emitters with spectrally matched photonic mirrors, a team of scientists with Berkeley Lab and the University of Illinois created solar cells that collect blue photons at 30 times the concentration of conventional solar cells, the highest luminescent concentration factor ever recorded. This breakthrough paves the way for the future development of low-cost solar cells that efficiently utilize the high-energy part of the solar spectrum.
“We’ve achieved a luminescent concentration ratio greater than 30 with an optical efficiency of 82-percent for blue photons,” says Berkeley Lab director Paul Alivisatos, who is also the Samsung Distinguished Professor of Nanoscience and Nanotechnology at the University of California Berkeley, and director of the Kavli Energy Nanoscience Institute (ENSI), was the co-leader of this research. “To the best of our knowledge, this is the highest luminescent concentration factor in literature to date.”
Luminescent solar concentrators featuring quantum dots and photonic mirrors
Luminescent solar concentrators featuring quantum dots and photonic mirrors suffer far less parasitic loss of photons than LSCs using molecular dyes as lumophores.
Alivisatos and Ralph Nuzzo of the University of Illinois are the corresponding authors of a paper in ACS Photonics describing this research entitled “Quantum Dot Luminescent Concentrator Cavity Exhibiting 30-fold Concentration”. Noah Bronstein, a member of Alivisatos’s research group, is one of three lead authors along with Yuan Yao and Lu Xu. Other co-authors are Erin O’Brien, Alexander Powers and Vivian Ferry.
The solar energy industry in the United States is soaring with the number of photovoltaic installations having grown from generating 1.2 gigawatts of electricity in 2008 to generating 20-plus gigawatts today, according to the U.S. Department of Energy (DOE). Still, nearly 70-percent of the electricity generated in this country continues to come from fossil fuels. SA Solar 5 191b940e-6e05-402a-bfbb-3e7be5f8a46f_16x9_600x338Low-cost alternatives to today’s photovoltaic solar panels are needed for the immense advantages of solar power to be fully realized. One promising alternative has been luminescent solar concentrators (LSCs).
Unlike conventional solar cells that directly absorb sunlight and convert it into electricity, an LSC absorbs the light on a plate embedded with highly efficient light-emitters called “lumophores” that then re-emit the absorbed light at longer wavelengths, a process known as the Stokes shift. This re-emitted light is directed to a micro-solar cell for conversion to electricity. Because the plate is much larger than the micro-solar cell, the solar energy hitting the cell is highly concentrated.
With a sufficient concentration factor, only small amounts of expensive III-V photovoltaic materials are needed to collect light from an inexpensive luminescent waveguide. However, the concentration factor and collection efficiency of the molecular dyes that up until now have been used as lumophores are limited by parasitic losses, including non-unity quantum yields of the lumophores, imperfect light trapping within the waveguide, and reabsorption and scattering of propagating photons.
“We replaced the molecular dyes in previous LSC systems with core/shell nanoparticles composed of cadmium selenide (CdSe) cores and cadmium sulfide (CdS) shells that increase the Stokes shift while reducing photon re-absorption,” says Bronstein.
“The CdSe/CdS nanoparticles enabled us to decouple absorption from emission energy and volume, which in turn allowed us to balance absorption and scattering to obtain the optimum nanoparticle,” he says. “Our use of photonic mirrors that are carefully matched to the narrow bandwidth of our quantum dot lumophores allowed us to achieve waveguide efficiency exceeding the limit imposed by total internal reflection.”
In their ACS Photonics paper, the collaborators express confidence that future LSC devices will achieve even higher concentration ratios through improvements to the luminescence quantum yield, waveguide geometry, and photonic mirror design.
The success of this CdSe/CdS nanoparticle-based LSC system led to a partnership between Berkeley Lab, the University of Illinois, Caltech and the National Renewable Energy Lab (NREL) on a new solar concentrator project. At the recent Clean Energy Summit held in Las Vegas, President Obama and Energy Secretary Ernest Moniz announced this partnership will receive a $3 million grant for the development of a micro-optical tandem LCS under MOSAIC, the newest program from DOE’s ARPA-E. MOSAIC stands for Micro-scale Optimized Solar-cell Arrays with Integrated Concentration.
The LCS work reported in this story was carried out through the U.S. Department of Energy’s Energy Frontier Research Center program and the National Science Foundation.
Source: By Lynn Yarris, Berkeley Lab

Argone NL 090115 114727

 

Scientists at the U.S. Department of Energy’s Argonne National Laboratory have developed a new fuel cell catalyst using earthly abundant materials with performance that is comparable to platinum in laboratory tests. If commercially viable, the new catalyst could replace platinum in electric cars powered by fuel cells instead of batteries, which would greatly extend the range of electric vehicles and eliminate the need for recharging.

Fuel cells generate electricity by using hydrogen from a fuel tank with oxygen in the air. The only waste product emitted to the environment is water.

But fuel cells are expensive, largely because they depend on the precious metal platinum to cause the hydrogen-oxygen reaction. Argonne’s fuel cell catalyst replaces much of the platinum with a non-precious metal.

“Platinum represents about 50 percent of the cost of a fuel cell stack, so replacing or reducing platinum is essential to lowering the price of fuel cell vehicles,” said Di-Jia Liu, who led the Argonne team. Their catalyst replaces all the platinum in the fuel cell’s cathode, which usually requires four times as much platinum as the anode, and their new electrode design also optimizes the flow of protons and electrons within the fuel cell and the removal of water.

Many automakers see sales of vehicles powered by fuel cells as eventually outpacing battery-powered electric vehicles for several reasons: fuel-cell vehicles emit only water, can travel over 300 miles between fill ups, can be refilled quickly and place no burden on the electrical grid because they don’t need recharging.

Since both technologies lack refilling or recharging infrastructures and are expensive, both are currently suitable mainly for early adopters and use in corporate fleets. But this may change, if advances made by Argonne researchers can be realized in commercial fuel-cell vehicles.

Fuel cells generate electricity to propel vehicles through electrochemical reactions between onboard hydrogen fuel and oxygen in the air. Hydrogen molecules are stripped of electrons at the fuel cell’s anode, becoming protons that travel through a polymer electrolyte membrane to the cathode, where they react with electrons and oxygen to form water.

“In order for a fuel cell to work,” Liu explained, “the catalyst must be densely packed with active sites that are uniformly distributed throughout the cathode and directly connected to the arriving protons and electrons, while maintaining easy access to oxygen. The catalyst should also have an architecture that can readily channel away the produced water.” No conventional method for preparing carbon-based platinum or non-precious metal catalysts can meet all these criteria, Liu added.

In a paper recently published in the Proceedings of the National Academy of Sciences of the United States of America, the team led by Liu reported on a new method of synthesizing a highly efficient, nanofibrous non-precious metal catalyst by electrospinning a polymer solution containing a mixture of ferrous organometallics and metal-organic frameworks. Following thermal activation, the new catalyst delivered an unprecedented level of catalytic activity in actual fuel cell tests.

“The new catalyst offers a unique carbon nano-network architecture made of microporous nanofibers interconnected through a macroporous framework,” Liu explained. “Not only do the active sites inside the micropores within individual fibers catalyze chemical reactions effectively, but the macroporous voids between the fibers transport oxygen and water efficiently to and from the active sites. The continuous nano-networks also make the catalytic electrode highly conductive in charge transfer.”

The paper, “Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network,” was published online on August 10, 2015.

The research was supported by the U.S. Department of Energy’s Office of Science and the Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. With employees from more than 60 nations, Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. Argonne is supported by the Office of Science of the U.S. Department of Energy.

The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Moly Berkley Jim-Schuck-MoS2_v5_2_Web-300x300  Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have used a unique nano-optical probe to study the effects of illumination on two-dimensional semiconductors at the molecular level. Working at the Molecular Foundry, a DOE Office of Science User Facility, the scientific team used the “Campanile” probe they developed to make some surprising discoveries about molybdenum disulfide, a member of a family of semiconductors, called “transition metal dichalcogenides (TMDCs), whose optoelectronic properties hold great promise for future nanoelectronic and photonic devices.

“The Campanile probe’s remarkable resolution enabled us to identify significant nanoscale optoelectronic heterogeneity in the interior regions of monolayer crystals of molybdenum disulfide, and an unexpected, approximately 300 nanometer wide, energetically disordered edge region,” says James Schuck, a staff scientist with Berkeley Lab’s Materials Sciences Division. Schuck led this study as well as the team that created the Campanile probe, which won a prestigious R&D 100 Award in 2013 for combining the advantages of scan/probe microscopy and optical spectroscopy.

“This disordered edge region, which has never been seen before, could be extremely important for any devices in which one wants to make electrical contacts,” Schuck says. “It might also prove critical to photocatalytic and nonlinear optical conversion applications.”

(From left)Jim Schuck, Wei Bao and Nicholas Borys at the Molecular Foundry where they made surprising discoveries about 2D MoS2, a promising TMDC semiconductor for future photonic and nanoelectronic devices. (Photo by Roy Kaltschmidt)

Schuck, who directs the Imaging and Manipulation of Nanostructures Facility at the Molecular Foundry, is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Visualizing nanoscale excitonic relaxation properties of disordered edges and grain boundaries in monolayer molybdenum disulfide.” The co-lead authors are Wei Bao and Nicholas Borys. (See below for a complete list of authors.)

2D-TMDCs rival graphene as potential successors to silicon for the next generation of high-speed electronics. Only a single molecule in thickness, 2D-TMDC materials boast superior energy efficiencies and a capacity to carry much higher current densities than silicon. However, since their experimental “discovery” in 2010, the performance of 2D-TMDC materials has lagged far behind theoretical expectations primarily because of a lack of understanding of 2D-TMDC properties at the nanoscale, particularly their excitonic properties. Excitons are bound pairs of excited electrons and holes that enable semiconductors to function in devices.

“The poor understanding of 2D-TMDC excitonic and other properties at the nanoscale is rooted in large part to the existing constraints on nanospectroscopic imaging,” Schuck says. “With our Campanile probe, we overcome nearly all previous limitations of near-field microscopy and are able to map critical chemical and optical properties and processes at their native length scales.”

Campanile-bellsThe Campanile probe, which draws its name from the landmark “Campanile” clock tower on the campus of the University of California at Berkeley, features a tapered, four-sided microscopic tip that is mounted on the end of an optical fiber. Two of the Campanile probe’s sides are coated with gold and the two gold layers are separated by just a few nanometers at the tip. The tapered design enables the Campanile probe to channel light of all wavelengths down into an enhanced field at the apex of the tip. The size of the gap between the gold layers determines the resolution, which can be below the diffraction optical limit.

In their new study, Schuck, Bao, Borys and their co-authors used the Campanile probe to spectroscopically map nanoscale excited-state/relaxation processes in monolayer crystals of molybdenum disulfide that were grown by chemical vapor deposition (CVD). Molybdenum disulfide is a 2D semiconductor that features high electrical conductance comparable to that of graphene, but, unlike graphene, has natural energy band-gaps, which means its conductance can be switched off.

“Our study revealed significant nanoscale optoelectronic heterogeneity and allowed us to quantify exciton-quenching phenomena at crystal grain boundaries,” Schuck said. “The discovery of the disordered edge region constitutes a paradigm shift from the idea that only a 1D metallic edge state is responsible for all the edge-related physics and photochemistry being observed in 2D-TMDCs. What’s happening at the edges of 2D-TMDC crystals is clearly more complicated than that. There’s a   mesoscopic disordered region that likely dominates most transport, nonlinear optical, and photocatalytic behavior near the edges of CVD-grown 2D-TMDCs.”

Comparison between image of MoS2 flake captured with Campanile probe and image of same flake captured with scanning confocal microscopy shows the Campanile probe’s enhanced resolution.

In this study, Schuck and his colleagues also discovered that the disordered edge region in molybdenum disulfide crystals harbors a sulfur deficiency that holds implications for future optoelectronic applications of this 2D-TMDC.

“Less sulfur means more free electrons are present in that edge region, which could lead to enhanced non-radiative recombination,” Schuck says. “Enhanced non-radiative recombination means that excitons created near a sulfur vacancy would live for a much shorter period of time.”

Schuck and his colleagues plan to next study the excitonic and electronic properties that may arise, as well as the creation of p-n junctions and quantum wells, when two disparate types of TMDCs are connected.

“We are also combining 2D-TMDC materials with so-called meta surfaces for controlling and manipulating the valley states and circular emitters that exist within these systems, as well as exploring localized quantum states that could act as near-ideal single-photon emitters and quantum-entangled Qubit states,” Schuck says.

In addition to Schuck, Bao, Borys and Weber-Bargioni, other co-authors of the Nature Communications paper are Changhyun Ko, Joonki Suh, Wen Fan, Andrew Thron, Yingjie Zhang, Alexander Buyanin, Jie Zhang, Stefano Cabrini, Paul Ashby, Alexander Weber-Bargioni, Sefaattin Tongay, Shaul Aloni, Frank Ogletree, Junqiao Wu and Miquel Salmeron.
This research was supported by the DOE Office of Science.

Additional Information

For more about the research of James Schuck and his group go here

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Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

South Africa II nanotechnology-india-brazil_26

By Michael Berger – Nanowerk. During 2002 and 2003, Nobel laureate Richard E. Smalley developed a list of the Top Ten Problems Facing Humanity over the next 50 years. The Richard E. Smalley Institute for Nanoscale Science and Technology at Rice University (which in May 2015 has been merged with the Rice Quantum Institute into a new entity: the Smalley-Curl Institute) has identified 5 of these problems as society’s Grand Challenges – and energy tops the list.

Since then, researchers around the world have demonstrated the potential for nanotechnology to be a key technology on the path to a sustainable energy future. Against the double-whammy backdrop of an energy challenge – the world’s appetite for energy keeps growing1 – plus a climate challenge – climate goals (2°C target) require substantial reduction in greenhouse gases (see: Climate change: Action, trends and implications for business. pdf) – it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.

Why is nanotechnology relevant here? Many effects important for energy happen at the nanoscale: In solar cells, for instance, photons can free electrons from a material, which can then flow as an electric current; the chemical reactions inside a battery or fuel cell release electrons which then move through an external circuit; or the role of catalysts in a plethora of chemical reactions. These are just a few examples where nanoscale engineering can significantly improve the efficiency of the underlying processes. The working principle of a solar cell

The working principle of a solar cell. (Image: University of Massachusetts Amherst)

Nanotechnologies are not tied exclusively to renewable energy technologies. While researchers are exploring ways in which nanotechnology could help us to develop energy sources, they also develop techniques to access and use fossil fuels much more efficiently. Corrosion resistant nanocoatings, nanostructured catalysts, and nanomembranes have been used in the extraction and processing of fossil fuels and in nuclear power. There is no silver bullet – nanotechnology applications for energy are extremely varied, reflecting the complexity of the energy sector, with a number of different markets along its value chain, including energy generation, transformation, distribution, storage, and usage. Nanotechnology has the potential to have a positive impact on all of these – albeit with varying effects.

Nanomaterials could lead to energy savings through weight reduction or through optimized function:

  • In the future, novel, nano-technologically optimized materials, for example plastics or metals with carbon nanotubes (CNTs), will make airplanes and vehicles lighter and therefore help reduce fuel consumption;
  • Novel lighting materials (OLED: organic light-emitting diodes) with nanoscale layers of plastic and organic pigments are being developed; their conversion rate from energy to light can apparently reach 50 % (compared with traditional light bulbs = 5%);
  • Nanoscale carbon black has been added to modern automobile tires for some time now to reinforce the material and reduce rolling resistance, which leads to fuel savings of up to 10%;
  • Self-cleaning or “easy-to-clean”-coatings, for example on glass, can help save energy and water in facility cleaning because such surfaces are easier to clean or need not be cleaned so often;
  • Nanotribological wear protection products as fuel or motor oil additives could reduce fuel consumption of vehicles and extend engine life;
  • Nanoparticles as flow agents allow plastics to be melted and cast at lower temperatures;
  • Nanoporous insulating materials in the construction business can help reduce the energy needed to heat and cool buildings.

Nanomaterials could improve energy generation and energy efficiencies:

  • Various nanomaterials can improve the efficiency of photovoltaic facilities;
  • Dye solar cells (‘Grätzel cells’) with nanoscale semiconductor materials mimic natural photosynthesis in green plants;
  • Plastics with carbon nanotubes as coatings on the rotor blades of wind turbines make these lighter and increase the energy yield;
  • Nano optimized lithium-ion batteries have an improved storage capacity as well as an increased lifespan and find use in electric vehicles for example;
  • Fuel cells with nanoscale ceramic materials for energy production require less energy and resources during manufacturing;
  • The effectiveness of catalytic converters in vehicles can be increased by applying catalytically active precious metals in the nanoscale size range.

We have compiled an overview of Nanotechnology in Energy that shows how nanotechnology innovations could impact each part of the value-added chain in the energy sector – energy sources; energy conversion; energy distribution; energy storage; and energy usage.

future energy nanotechnologyThe European GENNESYS project identified a range of nanomaterial application and requirements for future energy applications3. (click on image to enlarge) In the short term, energy nanotechnology is likely to have the greatest impact in the areas of efficiency of photovoltaics (among renewables, solar has by far the biggest global energy potential) and energy storage where it can help overcome current performance barriers and substantially improve the collection and conversion of solar energy. Nanotechnology for Solar Energy Collection and Conversion is one of the five Signature Initiatives funded by the U.S. National Nanotechnology Initiative. The goals are to enhance understanding of conversion and storage phenomena at the nanoscale, improve nanoscale characterization of electronic properties, and help enable economical nanomanufacturing of robust devices. The initiative has three major thrust areas:

  • – improve photovoltaic solar electricity generation;
  • – improve solar thermal energy generation and conversion; and
  • – improve solar-to-fuel conversions.

The thermodynamic limit of 80% efficiency is well beyond the capabilities of current photovoltaic technologies, whose laboratory performance currently approaches only 43% 2. Nanomaterials even make it possible to raise light yield of traditional crystalline silicon solar cells. By using cheaper, nanoscale materials than the current dominant technology (single-crystal silicon, which uses a large amount of fossil fuels for production), the cost of solar cells could be brought down. Numerous research labs are working on nanotechnology-enabled batteries to increase their efficiencies for electric vehicles, home, or grid storage systems. Improving the efficiency/storage capacity of batteries and supercapacitors with nanomaterials will have a substantial economical impact.

Graphene has already been demonstrated to have many promising applications in energy-related areas. (read more: “Graphene materials for energy storage applications“). Nanotechnology also has the potential to deliver the next generation lithium-ion batteries with improved performance, durability and safety at an acceptable cost (“The promise of nanotechnology for the next generation of lithium-ion batteries“).

A major push on basic research for energy technologies is coming from the U.S. Department of Energy, which since 2009 has invested nearly $800m as part of the Energy Frontier Research Center (EFRC) program. For example, the Joint Center for Artificial Photosynthesis (JCAP) has developed a nanowire-based design that incorporates two semiconductors to enhance absorption of light; or the Nanostructures for Electrical Energy Storage (NEES) EFRC Center has demonstrated that precise nanostructures can be constructed to test the limits of 3-D nanobatteries by designing billions of tiny batteries inside nanopores.

Against the double-whammy backdrop of an energy challenge and a climate challenge it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.

So where does that leave ‘nanotechnology’? It may not be the silver bullet, but nanomaterials and nanoscale applications will have an important role to play.

Notes 1) Energy demand grows by 37% to 2040 on planned policies, an average rate of growth of 1.1%. World electricity demand increases by almost 80% over the period 2012-2040. 1.6bn people still without access to electricity, thereof 950 million in sub-Saharan Africa. (Source: IEA World Energy Outlook 2014) 2) Source: NSI Solar White Paper (pdf) 3) Source: GENNESYS White paper

 


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