Lawrence Berkeley National Laboratory battery scientist Venkat Srinivasan chats with Sabin Russell, former San Francisco Chronicle reporter turned Berkeley Lab science writer. They explore the problems that prevent lithium-ion batteries from being widely used in electric, hybrid-electric, and plug-in-hybrid-electric vehicles. Series: “Lawrence Berkeley National Laboratory Summer Lecture Series” [Science] [Show]
The U.S. Department of Energy’s (DOE’s) Exascale Computing Project (ECP) today announced its first round of funding with the selection of 15 application development proposals for full funding and seven proposals for seed funding, representing teams from 45 research and academic organizations.
Exascale refers to high-performance computing systems capable of at least a billion billion calculations per second, or a factor of 50 to 100 times faster than the nation’s most powerful supercomputers in use today.
The 15 awards being announced total $39.8 million, targeting advanced modeling and simulation solutions to specific challenges supporting key DOE missions in science, clean energy and national security, as well as collaborations such as the Precision Medicine Initiative with the National Institutes of Health’s National Cancer Institute.
Of the proposals announced that are receiving full funding, two are being led by principal investigators at the DOE’s Argonne National Laboratory:
Computing the Sky at Extreme Scales equips cosmologists with the ability to design foundational simulations to create “virtual universes” on demand at the extreme fidelities demanded by future multi-wavelength sky surveys. The new discoveries that will emerge from the combination of sky surveys and advanced simulation provided by the ECP will shed more light on three key ingredients of our universe: dark energy, dark matter and inflation. All three of these concepts reach beyond the known boundaries of the Standard Model of particle physics.Salman Habib, Principal Investigator, Argonne National Laboratory, with Los Alamos National Laboratory and Lawrence Berkeley National Laboratory.
Exascale Deep Learning and Simulation Enabled Precision Medicine for Cancer focuses on building a scalable deep neural network code called the CANcer Distributed Learning Environment (CANDLE) that addresses three top challenges of the National Cancer Institute: understanding the molecular basis of key protein interactions, developing predictive models for drug response and automating the analysis and extraction of information from millions of cancer patient records to determine optimal cancer treatment strategies.Rick Stevens, Principal Investigator, Argonne National Laboratory, with Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Oak Ridge National Laboratory and the National Cancer Institute.
Additionally, a third project led by Argonne will be receiving seed funding:
Multiscale Coupled Urban Systems will create an integrated modeling framework comprising data curation, analytics, modeling and simulation components that will equip city designers, planners and managers to scientifically develop and evaluate solutions to issues that affect cities now and in the future. The framework will focus first on integrating urban atmosphere and infrastructure heat exchange and air flow; building energy demand at district or city-scale, generation and use; urban dynamics and socioeconomic models; population mobility and transportation; and hooks to expand to include energy systems (biofuels, electricity and natural gas) and water resources.Charlie Catlett, Principal Investigator, Argonne National Laboratory, with Lawrence Berkeley National Laboratory, National Renewable Energy Laboratory, Oak Ridge National Laboratory and Pacific Northwest National Laboratory.
The application efforts will help guide DOE’s development of a U.S. exascale ecosystem as part of President Obama’s National Strategic Computing Initiative. DOE, the U.S. Department of Defense and the National Science Foundation have been designated as lead agencies, and ECP is the primary DOE contribution to the initiative.
The ECP’s multiyear mission is to maximize the benefits of high-performance computing for U.S. economic competitiveness, national security and scientific discovery. In addition to applications, the DOE project addresses hardware, software, platforms and workforce development needs critical to the effective development and deployment of future exascale systems.
Leadership of the ECP comes from six DOE national laboratories: the Office of Science’s Oak Ridge, Argonne and Lawrence Berkeley national labs and the National Nuclear Security Administration’s (NNSA’s) Lawrence Livermore, Los Alamos and Sandia national labs.
The Exascale Computing Project is a collaborative effort of two DOE organizations — the Office of Science and the NNSA. As part of President Obama’s National Strategic Computing initiative, ECP was established to develop a capable exascale ecosystem, encompassing applications, system software, hardware technologies and architectures, and workforce development to meet the scientific and national security mission needs of DOE in the mid-2020s timeframe.
Established by Congress in 2000, NNSA is a semi-autonomous agency within DOE responsible for enhancing national security through the military application of nuclear science. NNSA maintains and enhances the safety, security, and effectiveness of the U.S. nuclear weapons stockpile without nuclear explosive testing; works to reduce the global danger from weapons of mass destruction; provides the U.S. Navy with safe and effective nuclear propulsion; and responds to nuclear and radiological emergencies in the United States and abroad.
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. 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. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’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, visit the Office of Science website.
From energy efficiency to carbon capture, Berkeley Lab scientists are on it.
Berkeley Lab researchers are using the science of the very small to help solve big challenges. That’s because, at the nanoscale—the scale of molecules and proteins—new and exciting properties emerge that can possibly be put to use.
Here are five projects, now underway and recently highlighted in the News Center, which promise big results from the smallest of building blocks:
This “cool” DIY retrofit tech could improve the energy efficiency of windows and save money. Researchers are developing a polymer-based heat-reflective coating that makes use of the unusual molecular architecture of a polymer.
It has the potential to be painted on windows at one-tenth the cost of current retrofit approaches. Window films on the market today reflect infrared solar energy back to the sky while allowing visible light to pass through, but a professional contractor is needed to install them. A low-cost option could significantly expand adoption and result in potential annual energy savings equivalent to taking 5 million cars off the road.
Researchers have found a new way to produce nanoscale wires that can serve as tiny, tunable lasers. The excellent performance of these tiny lasers is promising for the field of optoelectronics, which is focused on combining electronics and light to transmit data, among other applications. Miniaturizing lasers to the nanoscale could further revolutionize computing, bringing light-speed data transmission to desktop, and ultimately, handheld computing devices.
Scientists are developing nano sponges that could capture carbon from power plants before it enters the atmosphere. Initial tests show the hybrid membrane, composed of nano-sized cages (called metal-organic frameworks) and a polymer, is eight times more carbon dioxide permeable than membranes composed only of the polymer.
Boosting carbon dioxide permeability is a big goal in efforts to develop carbon capture materials that are energy efficient and cost competitive. Watch this video for more on this technology.
Scientists have recently reengineered a building block of a nanocompartment that occurs naturally in bacteria, greatly expanding the potential of nanocompartments to serve as custom-made chemical factories. Researchers hope to tailor this new use to produce high-value chemical products, such as medicines, on demand.
The sturdy nanocompartments are formed by hundreds of copies of just three different types of proteins. Their natural counterparts, known as bacterial microcompartments, encase a wide variety of enzymes that carry out highly specialized chemistry in bacteria.
Researchers have discovered a family of nature-inspired polymers that, when placed in water, spontaneously assemble into hollow crystalline nanotubes. What’s more, the nanotubes can be tuned to all have the same diameter of between five and ten nanometers. Controlling the diameter of nanotubes, and the chemical groups exposed in their interior, enables scientists to control what goes through. Nanotubes have the potential to be incredibly useful, from delivering cancer-fighting drugs inside cells to desalinating seawater.
The Science of Small Revealed Using a Penny
Just how small can nanoscience get? Here’s a great example using an American penny from the Molecular Foundry.
In this video, the letters that spell Molecular Foundry were written with a beam of electrons fired at the surface. The smallest feature is 20 nanometers, or roughly 100 atoms. As the video zooms out, you lose sight of Molecular Foundry and see the Berkeley Lab logo, which was written with a beam of charged gallium atoms. As you continue to zoom out, you see an 18 hour timelapse of Abraham Lincoln’s face, again written with gallium atoms. Finally, all of this is done within the Lincoln Memorial side of the penny as it is removed from the focused ion beam.
Photolithography, which literally means writing with light, is the foundation for most top-down fabrication of things like microprocessors. However, because of something called the diffraction limit, photolithography is limited to devices that have features no smaller than the wavelength of the light used, often in the 100s of nanometers. As a result, things smaller than light like atoms and electrons must be used.
In an advance that helps pave the way for next-generation electronics and computing technologies—and possibly paper-thin gadgets —scientists with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) developed a way to chemically assemble transistors and circuits that are only a few atoms thick.
What’s more, their method yields functional structures at a scale large enough to begin thinking about real-world applications and commercial scalability.
They report their research online July 11 in the journal Nature Nanotechnology.
The scientists controlled the synthesis of a transistor in which narrow channels were etched onto conducting graphene, and a semiconducting material called a transition-metal dichalcogenide, or TMDC, was seeded in the blank channels. Both of these materials are single-layered crystals and atomically thin, so the two-part assembly yielded electronic structures that are essentially two-dimensional. In addition, the synthesis is able to cover an area a few centimeters long and a few millimeters wide.
“This is a big step toward a scalable and repeatable way to build atomically thin electronics or pack more computing power in a smaller area,” says Xiang Zhang, a senior scientist in Berkeley Lab’s Materials Sciences Division who led the study.
Zhang also holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley. Other scientists who contributed to the research include Mervin Zhao, Yu Ye, Yang Xia, Hanyu Zhu, Siqi Wang, and Yuan Wang from UC Berkeley as well as Yimo Han and David Muller from Cornell University.
Their work is part of a new wave of research aimed at keeping pace with Moore’s Law, which holds that the number of transistors in an integrated circuit doubles approximately every two years. In order to keep this pace, scientists predict that integrated electronics will soon require transistors that measure less than ten nanometers in length.
Transistors are electronic switches, so they need to be able to turn on and off, which is a characteristic of semiconductors. However, at the nanometer scale, silicon transistors likely won’t be a good option. That’s because silicon is a bulk material, and as electronics made from silicon become smaller and smaller, their performance as switches dramatically decreases, which is a major roadblock for future electronics.
Researchers have looked to two-dimensional crystals that are only one molecule thick as alternative materials to keep up with Moore’s Law. These crystals aren’t subject to the constraints of silicon.
In this vein, the Berkeley Lab scientists developed a way to seed a single-layered semiconductor, in this case the TMDC molybdenum disulfide (MoS2), into channels lithographically etched within a sheet of conducting graphene. The two atomic sheets meet to form nanometer-scale junctions that enable graphene to efficiently inject current into the MoS2. These junctions make atomically thin transistors.
“This approach allows for the chemical assembly of electronic circuits, using two-dimensional materials, which show improved performance compared to using traditional metals to inject current into TMDCs,” says Mervin Zhao, a lead author and Ph.D. student in Zhang’s group at Berkeley Lab and UC Berkeley.
Optical and electron microscopy images, and spectroscopic mapping, confirmed various aspects related to the successful formation and functionality of the two-dimensional transistors.
In addition, the scientists demonstrated the applicability of the structure by assembling it into the logic circuitry of an inverter. This further underscores the technology’s ability to lay the foundation for a chemically assembled atomic computer, the scientists say.
“Both of these two-dimensional crystals have been synthesized in the wafer scale in a way that is compatible with current semiconductor manufacturing. By integrating our technique with other growth systems, it’s possible that future computing can be done completely with atomically thin crystals,” says Zhao.
Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn’t be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers—with water as the only byproduct of combustion.
While there remain scientific challenges to making hydrogen-based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like hydrogen fuel cell—which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets—to push its performance forward in key areas.
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.
These graphene-encapsulated magnesium crystals act as “sponges” for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall “tank” size.
“Among metal hydride-based materials for hydrogen storage for fuel-cell vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability,” said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications.
In a hydrogen fuel cell-powered vehicle using these materials, known as a “metal hydride” (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.
Jeff Urban, a Berkeley Lab staff scientist and co-author, said, “This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity—concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials.”
The research, conducted at Berkeley Lab’s Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials—Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab’s lead scientist for that effort.
The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.
Hydrogen-fuel-cell vehicles haven’t yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.
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.
A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the “gravimetric energy density,” is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.
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, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.
Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.
The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials’ fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.
Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.
Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective “one pan” technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals’ structure using X-rays at Berkeley Lab’s Advanced Light Source. The X-ray studies showed how hydrogen gas pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.
“It is stable in air, which is important,” Cho said.
Next steps in the research will focus on using different types of catalysts—which can improve the speed and efficiency of chemical reactions—to further improve the fuel cell’s conversion of electrical current, and in studying whether different types of material can also improve the fuel cell’s overall capacity, Cho said.
More information: Eun Seon Cho et al. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage, Nature Communications (2016). DOI: 10.1038/ncomms10804
California is committed to 33 percent energy from renewable resources by 2020. With that deadline fast approaching, researchers across the state are busy exploring options.
Solar energy is attractive but for widespread adoption, it requires transformation into a storable form. This week in ACS Central Science, researchers report that nanowires made from multiple metal oxides could put solar ahead in this race.
One way to harness solar power for broader use is through photoelectrochemical (PEC) water splitting that provides hydrogen for fuel cells. Many materials that can perform the reaction exist, but most of these candidates suffer from issues, ranging from efficiency to stability and cost.
Peidong Yang and colleagues designed a system where nanowires from one of the most commonly used materials (TiO2) acts as a “host” for “guest” nanoparticles from another oxide called BiVO4. BiVO4 is a newly introduced material that is among the best ones for absorbing light and performing the water splitting reaction, but does not carry charge well while TiO2 is stable, cheap and an efficient charge carrier but does not absorb light well.
Together with a unique studded nanowire architecture, the new system works better than either material alone.
The authors state their approach can be used to improve the efficiencies of other photoconversion materials.
We report the use of Ta:TiO2|BiVO4 as a photoanode for use in solar water splitting cells. This host−guest system makes use of the favorable band alignment between the two semiconductors. The nanowire architecture allows for simultaneously high light absorption and carrier collection for efficient solar water oxidation.
Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.
Harnessing energy from sunlight is a means of meeting the large global energy demand in a cost-effective and environmentally benign manner. However, to provide constant and stable power on demand, it is necessary to convert sunlight into an energy storage medium.(1) An example of such a method is the production of hydrogen by photoelectrochemical (PEC) water splitting. The direct splitting of water can be achieved using a single semiconductor; however, due to the voltage requirement of the water splitting reaction and the associated kinetic overpotentials, only wide-band-gap materials can perform overall water splitting, limiting the efficiency due to insufficient light absorption.(2) To address this issue, a dual-band-gap z-scheme system can be utilized, with a semiconductor photoanode and photocathode to perform the respective oxidation and reduction reactions.(3) This approach allows for the use of lower-band-gap materials that can absorb complementary portions of the solar spectrum and yield higher solar-to-fuel efficiencies.(4, 5) In this integrated system, the charge flux is matched in both light absorbers of the photoelectrochemical cell. Therefore, the overall performance is determined by the limiting component. In most photoelectrosynthetic cells, this limiting component is the semiconductor photoanode.(6)
Metal oxides have been heavily researched as photoanode materials since few conventional light absorber materials are stable at the highly oxidizing conditions required for water oxidation.(7) However, the most commonly studied binary oxide, TiO2, has a band gap that is too large to absorb sunlight efficiently (∼3.0 eV), consequently limiting its achievable photocurrent.(8) While promising work has recently been done on stabilizing conventional light absorbers such as Si,(9) GaAs,(10) and InP,(11) the photovoltage obtained by these materials thus far has been insufficient to match with smaller-band-gap photocathode materials such as Si and InP in a dual absorber photoelectrosynthetic cell.(12, 13) Additionally, these materials have high production and processing costs. Small-band-gap metal oxides that absorb visible light and can be inexpensively synthesized, such as WO3, Fe2O3, and BiVO4, are alternative materials that hold promise to overcome these limitations.(14-16) Among these metal oxides, BiVO4 has emerged as one of the most promising materials due to its relatively small optical band gap of ∼2.5 eV and its negative conduction band edge (∼0 V versus RHE).(17, 18) Under air mass 1.5 global (AM1.5G) solar illumination, the maximum achievable photocurrent for water oxidation using BiVO4 is ∼7 mA/cm2.(16) However, the water oxidation photocurrent obtained in practice for BiVO4 is substantially lower than this value, mainly due to poor carrier transport properties, with electron diffusion lengths shorter than the film thickness necessary to absorb a substantial fraction of light.(17)
One approach for addressing this problem is to use two separate materials for the tasks of light absorption and carrier transport. To maximize performance, a conductive and high surface area support material (“host”) is used, which is coated with a highly dispersed visible light absorber (“guest”). This architecture allows for efficient use of absorbed photons due to the proximity of the semiconductor liquid junction (SCLJ). This strategy has been employed in dye sensitized (DSSC) and quantum dot sensitized solar cells (QDSSC).(19, 20) Using a host–guest scheme can improve the performance of photoabsorbing materials with poor carrier transport but relies upon appropriate band alignment between the host and guest. Namely, the electron affinity of the host should be larger, to favor electron transfer from guest to host without causing a significant loss in open-circuit voltage.(21) Nanowire arrays provide several advantages for use as the host material as they allow high surface area loading of the guest material, enhanced light scattering for improved absorption, and one-dimensional electron transport to the back electrode.(22) Therefore, nanowire arrays have been used as host materials in DSSCs, QDSSCs, and hybrid perovskite solar cells.(23-25) In photoelectrosynthetic cells, host–guest architectures have been utilized for oxide photoanodes such as Fe2O3|TiSi2,(26) Fe2O3|WO3,(27) Fe2O3|SnO2,(28) and Fe2TiO5|TiO2.(29) For BiVO4, it has been studied primarily with WO3|BiVO4,(30-32) ZnO|BiVO4,(33) and anatase TiO2|BiVO4.(34) While attractive for its electronic transport properties, ZnO is unstable in aqueous environments, and WO3 has the disadvantage of having a relatively positive flatband potential (∼0.4 V vs RHE)(14) resulting in potential energy losses for electrons as they are transferred from BiVO4 to WO3, thereby limiting the photovoltage of the combined system. Performance in the low potential region is critical for obtaining high efficiency in photoelectrosynthetic cells when coupled to typical p-type photocathode materials such as Si or InP.(12, 13) TiO2 is stable in a wide range of pH and has a relatively negative flat band potential (∼0.2 V vs RHE)(7) which does not significantly limit the photovoltage obtainable from BiVO4, while still providing a driving force for electron transfer. While TiO2 has intrinsically low mobility, doping TiO2 with donor type defects could increase the carrier concentration and thus the conductivity. Indeed, niobium and tantalum doped TiO2 have recently been investigated as potential transparent conductive oxide (TCO) materials.(35, 36) A host material with high carrier concentration could also ensure low contact resistance with the guest material.(37)
Using a solid state diffusion approach based on atomic layer deposition (ALD), we have previously demonstrated the ability to controllably and uniformly dope TiO2.(38) In this study we demonstrate a host–guest approach using Ta-doped TiO2 (Ta:TiO2) nanowires as a host and BiVO4 as a guest material. This host–guest nanowire architecture allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent of 2.1 mA/cm2 at 1.23 V vs RHE. We show that the synergistic effect of the host–guest structure results in higher performance than either pure TiO2 or BiVO4. We also experimentally demonstrate thermodynamically favorable band alignment between TiO2 and BiVO4 using spectroscopic and electrochemical methods, and study the band edge electronic structure of the TiO2 and BiVO4 using X-ray absorption and emission spectroscopies.
Article adapted from a American Chemical Society news release. To Read the FULL release, please click on the link provided below.
Publication: TiO2/BiVO4 Nanowire Heterostructure Photoanodes Based on Type II Band Alignment. Resasco, J et al. ACS Central Science (3 February, 2016): Click here to view.
Genesis Nanotechnology – “Great Things from Small Things”
Readers’ Note: Dr. Alivisatos (Berkeley) has been a pioneer of ‘nano-cystals’ and their potential applications. Most recently these ‘crystals’ or Quantum Dots have found their way into commercial application for Display Screens. However the much larger vision for QD’s has significant (“game changing”) implications for: Solar Energy, Bio-Medicine, Drug Theranostics & Delivery, Lighting and Hybrid-Materials (Coatings, Paints, Security Inks as examples). Enjoy the Video ~ Team GNT
SNOW: When quantum dots of different sizes are grouped together by the billions, they produce vivid colors that have changed the way we look at display screens. The initial research, funded by the NSF, has found its way into many applications, including a nanotechnology company called Nanosys, which produces 25 tons of quantum dot materials every year, enough for approximately 6 million 60 inch TVs.
ALIVISATOS: What we have here is a plastic film that contains inside of it quantum dots, very tiny, tiny crystals made out of semiconductors. It actually contains two sizes of nanoparticle – a very small size that emits a green color and a slightly larger size that emits a red color of light.
SNOW: This film is embedded into tablets, televisions, and laptops to enhance their displays with brilliant color.
ALIVISATOS: One of the things that we’ve learned about vision is that we have receptors in our eyes for green, red and blue colors. And if we want a really high quality display, we need to match the light emission from our display to the receptors in our eyes.
There are many different ways to make nano-materials but weaving, the oldest and most enduring method of making fabrics, has not been one of them – until now. An international collaboration led by scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, has woven the first three-dimensional covalent organic frameworks (COFs) from helical organic threads. The woven COFs display significant advantages in structural flexibility, resiliency and reversibility over previous COFs – materials that are highly prized for their potential to capture and store carbon dioxide then convert it into valuable chemical products.
“We have taken the art of weaving into the atomic and molecular level, giving us a powerful new way of manipulating matter with incredible precision in order to achieve unique and valuable mechanical properties,” says Omar Yaghi, a chemist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Chemistry Department, and is the co-director of the Kavli Energy NanoScience Institute (Kavli-ENSI).
“Weaving in chemistry has been long sought after and is unknown in biology,” Yaghi says. “However, we have found a way of weaving organic threads that enables us to design and make complex two- and three-dimensional organic extended structures.”
Yaghi is the corresponding author of a paper in Science reporting this new technique. The paper is titled “Weaving of organic threads into a crystalline covalent organic framework.” The lead authors are Yuzhong Liu, Yanhang Ma and Yingbo Zhao. Other co-authors are Xixi Sun, Felipe Gándara, Hiroyasu Furukawa, Zheng Liu, Hanyu Zhu, Chenhui Zhu, Kazutomo Suenaga, Peter Oleynikov, Ahmad Alshammari, Xiang Zhang and Osamu Terasaki.
COFs and their cousin materials, metal organic frameworks (MOFs), are porous three-dimensional crystals with extraordinarily large internal surface areas that can absorb and store enormous quantities of targeted molecules. Invented by Yaghi, COFs and MOFs consist of molecules (organics for COFs and metal-organics for MOFs) that are stitched into large and extended netlike frameworks whose structures are held together by strong chemical bonds. Such frameworks show great promise for, among other applications, carbon sequestration.
Through another technique developed by Yaghi, called “reticular chemistry,” these frameworks can also be embedded with catalysts to carry out desired functions: for example, reducing carbon dioxide into carbon monoxide, which serves as a primary building block for a wide range of chemical products including fuels, pharmaceuticals and plastics.
In this latest study, Yaghi and his collaborators used a copper(I) complex as a template for bringing threads of the organic compound “phenanthroline” into a woven pattern to produce an immine-based framework they dubbed COF-505. Through X-ray and electron diffraction characterizations, the researchers discovered that the copper(I) ions can be reversibly removed or restored to COF-505 without changing its woven structure. Demetalation of the COF resulted in a tenfold increase in its elasticity and remetalation restored the COF to its original stiffness.
“That our system can switch between two states of elasticity reversibly by a simple operation, the first such demonstration in an extended chemical structure, means that cycling between these states can be done repeatedly without degrading or altering the structure,” Yaghi says. “Based on these results, it is easy to imagine the creation of molecular cloths that combine unusual resiliency, strength, flexibility and chemical variability in one material.”
Yaghi says that MOFs can also be woven as can all structures based on netlike frameworks. In addition, these woven structures can also be made as nanoparticles or polymers, which means they can be fabricated into thin films and electronic devices.
“Our weaving technique allows long threads of covalently linked molecules to cross at regular intervals,” Yaghi says. “These crossings serve as points of registry, so that the threads have many degrees of freedom to move away from and back to such points without collapsing the overall structure, a boon to making materials with exceptional mechanical properties and dynamics.”
Berkeley 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.”
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.
“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.
“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.”
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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.
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.