ASU and Stanford Researchers Achieve Record Breaking Efficiency with Tandem (Perovskite + Silicon) Solar Cell

ecee-perovskite-silicon-tandem-cell-pz-0035-w-1280x640Above: A perovskite/silicon tandem solar cell, created by research teams from Arizona State University and Stanford University, capable of record-breaking sunlight-to-electricity conversion efficiency. Photographer: Pete Zrioka/ASU

Some pairs are better together than their individual counterparts — peanut butter and chocolate, warm weather and ice cream, and now, in the realm of photovoltaic technology, silicon and perovskite.

As existing solar energy technologies near their theoretical efficiency limits, researchers are exploring new methods to improve performance — such as stacking two photovoltaic materials in a tandem cell. Collaboration between researchers at Arizona State University and Stanford University has birthed such a cell with record-breaking conversion efficiency — effectively finding the peanut butter to silicon’s chocolate.


The results of their work, published February 17 in Nature Energy, outline the use of perovskite and silicon to create a tandem solar cell capable of converting sunlight to energy with an efficiency of 23.6 percent, just shy of the all-time silicon efficiency record.

“The best silicon solar cell alone has achieved 26.3 percent efficiency,” says Zachary Holman, an assistant professor of electrical engineering at the Ira A. Fulton Schools of Engineering. “Now we’re gunning for 30 percent with these tandem cells, and I think we could be there within two years.”

Assistant Professor Zachary Holman, holds one of the many solar cells his research group has created. Photographer: Jessica Hochreiter/ASU

Silicon solar cells are the backbone of a $30 billion a year industry, and this breakthrough shows that there’s room for significant improvement within such devices by finding partner materials to boost efficiency.

The high-performance tandem cell’s layers are each specially tuned to capture different wavelengths of light. The top layer, composed of a perovskite compound, was designed to excel at absorbing visible light. The cell’s silicon base is tuned to capture infrared light.

Perovskite, a cheap, easily manufacturable photovoltaic material, has emerged as a challenger to silicon’s dominance in the solar market. Since its introduction to solar technology in 2009, the efficiency of perovskite solar cells has increased from 3.8 percent to 22.1 percent in early 2016, according to the National Renewable Energy Laboratory.

The perovskite used in the tandem cell came courtesy of Stanford researchers Professor Michael McGehee and doctoral student Kevin Bush, who fabricated the compound and tested the materials.

The research team at ASU provided the silicon base and modeling to determine other material candidates for use in the tandem cell’s supporting layers.


 Zhengshan (Jason) Yu, an electrical engineering doctoral student at ASU, holds up a tiny black solar cell which is flanked by two conductors. The small cell has yielded big improvements, resulting in a record-breaking 23.6 percent efficiency rate.

Though low-cost and highly efficient, perovskites have been limited by poor stability, degrading at a much faster rate than silicon in hot and humid environments. Additionally, perovskite solar cells have suffered from parasitic absorption, in which light is absorbed by supporting layers in the cell that don’t generate electricity.

“We have improved the stability of the perovskite solar cells in two ways,” says McGehee, a materials science and engineering professor at Stanford’s School of Engineering. “First, we replaced an organic cation with cesium. Second, we protected the perovskite with an impermeable indium tin oxide layer that also functions as an electrode.”

Though McGehee’s compound achieves record stability, perovskites remain delicate materials, making it difficult to employ in tandem solar technology.

“In many solar cells, we put a layer on top that is both transparent and conductive,” says Holman, a faculty member in the School of Electrical, Computer and Energy Engineering. “It’s transparent so light can go through and conductive so we can take electrical charges off it.”

This top conductive layer is applied using a process called sputtering deposition, which historically has led to damaged perovskite cells. However, McGehee was able to apply a tin oxide layer with help from chemical engineering Professor Stacey Bent and doctoral student Axel Palmstrom of Stanford. The pair developed a thin layer that protects the delicate perovskite from the deposition of the final conductive layer without contributing to parasitic absorption, further boosting the cell’s efficiency.

The deposition of the final conductive layer wasn’t the only engineering challenge posed by integrating perovskites and silicon.

“It was difficult to apply the perovskite itself without compromising the performance of the silicon cell,” says Zhengshan (Jason) Yu, an electrical engineering doctoral student at ASU.

Silicon wafers are placed in a potassium hydroxide solution during fabrication, which creates a rough, jagged surface. This texture, ideal for trapping light and generating more energy, works well for silicon, but perovskite prefers a smooth — and unfortunately reflective — surface for deposition.

Additionally, the perovskite layer of the tandem cell is less than a micron thick, opposed to the 250-micron thick silicon layer. This means when the thin perovskite layer was deposited, it was applied unevenly, pooling in the rough silicon’s low points and failing to adhere to its peaks.

Yu developed a method to create a planar surface only on the front of the silicon solar cell using a removable, protective layer. This resulted in a smooth surface on one side of the cell, ideal for applying the perovskite, while leaving the backside rough, to trap the weakly-absorbed near-infrared light in the silicon.

“With the incorporation of a silicon nanoparticle rear reflector, this infrared-tuned silicon cell becomes an excellent bottom cell for tandems,” says Yu.


The success of the tandem cell is built on existing achievements from both teams of researchers. In October 2016, McGehee and post-doctoral scholar Tomas Leijtens fabricated an all-perovskite cell capable of 20.3 percent efficiency. The high-performance cell was achieved in part by creating a perovskite with record stability, marking McGehee’s group as one of the first teams to devote research efforts to fabricating stable perovskite compounds.

Likewise, Holman has considerable experience working with silicon and tandem cells.

“We’ve tried to position our research group as the go-to group in the U.S. for silicon bottom cells for tandems,” says Holman, who’s been pursuing additional avenues to create high-efficiency tandem solar cells.

In fact, Holman and Yu published a comment in Nature Energy in September 2016 outlining the projected efficiencies of different cell combinations in tandems.

“People often ask, ‘given the fundamental laws of physics, what’s the best you can do?’” says Holman. “We’ve asked and answered a different, more useful question: Given two existing materials, if you could put them together, ideally, what would you get?”’

The publication is a sensible guide to designing a tandem solar cell, specifically with silicon as the bottom solar cell, according to Holman.

It calculates what the maximum efficiency would be if you could pair two existing solar cells in a tandem without any performance loss. The guide has proven useful in directing research efforts to pursue the best partner materials for silicon.

“We have eight projects with different universities and organizations, looking at different types of top cells that go on top of silicon,” says Holman. “So far out of all our projects, our perovskite/silicon tandem cell with Stanford is the leader.”

Stanford University: Solving the “Storage Problem” for Renewable Energies: A New Cost Effective Re-Chargeable Aluminum Battery


One of the biggest missing links in renewable energy is affordable and high performance energy storage, but a new type of battery developed at Stanford University could be the solution.

Solar energy generation works great when the sun is shining [duh…like taking a Space Mission to the Sun .. but only at night! :-)] and wind energy is awesome when it’s windy (double duh…), but neither is very helpful for the grid after dark and when the air is still. That’s long been one of the arguments against renewable energy, even if there are plenty of arguments for developing additional solar and wind energy installations without large-scale energy storage solutions in place. However, if low-cost and high performance batteries were readily available, it could go a long way toward a more sustainable and cleaner grid, and a pair of Stanford engineers have developed what could be a viable option for grid-scale energy storage.

With three relatively abundant and low-cost materials, namely aluminum, graphite, and urea, Stanford chemistry Professor Hongjie Dai and doctoral candidate Michael Angell have created a rechargeable battery that is nonflammable, very efficient, and has a long lifecycle.

“So essentially, what you have is a battery made with some of the cheapest and most abundant materials you can find on Earth. And it actually has good performance. Who would have thought you could take graphite, aluminum, urea, and actually make a battery that can cycle for a pretty long time?” – Dai

A previous version of this rechargeable aluminum battery was found to be efficient and to have a long life, but it also employed an expensive electrolyte, whereas the latest iteration of the aluminum battery uses urea as the base for the electrolyte, which is already produced in large quantities for fertilizer and other uses (it’s also a component of urine, but while a pee-based home battery might seem like just the ticket, it’s probably not going to happen any time soon).

According to Stanford, the new development marks the first time urea has been used in a battery, and because urea isn’t flammable (as lithium-ion batteries are), this makes it a great choice for home energy storage, where safety is of utmost importance. And the fact that the new battery is also efficient and affordable makes it a serious contender when it comes to large-scale energy storage applications as well.

“I would feel safe if my backup battery in my house is made of urea with little chance of causing fire.” – Dai

According to Angell, using the new battery as grid storage “is the main goal,” thanks to the high efficiency and long life cycle, coupled with the low cost of its components. By one metric of efficiency, called Coulombic efficiency, which measures the relationship between the unit of charge put into the battery and the output charge, the new battery is rated at 99.7%, which is high.WEF solarpowersavemoney-628x330

In order to meet the needs of a grid-scale energy storage system, a battery would need to last at least a decade, and while the current urea-based aluminum ion batteries have been able to last through about 1500 charge cycles, the team is still looking into improving its lifetime in its goal of developing a commercial version.

The team has published some of its results in the Proceedings of the National Academy of Sciences, under the title “High Coulombic efficiency aluminum-ion battery using an AlCl3-urea ionic liquid analog electrolyte.”


PNL Battery Storage Systems 042016 rd1604_batteriesGrid-scale energy storage to manage our electricity supply would benefit from batteries that can withstand repeated cycling of discharging and charging. Current lithium-ion batteries have lifetimes of only 1,000-3,000 cycles. Now a team of researchers from Stanford University, Taiwan, and China have made a research prototype of an inexpensive, safe aluminum-ion battery that can withstand 7,500 cycles. In the aluminum-ion battery, one electrode is made from affordable aluminum, and the other is composed of carbon in the form of graphite.

Read: A step towards new, faster-charging, and safer batteries


Stanford University: Researchers Make Wires That Are Just Three Atoms Wide


diamondoid-penny-fullresResearchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids — the smallest possible bits of diamond — to self-assemble atoms, LEGO-style, into the thinnest possible electrical wires, just three atoms wide.


Scientists at Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids – the smallest possible bits of diamond – to assemble atoms into the thinnest possible electrical wires, just three atoms wide.

By grabbing various types of atoms and putting them together building-block style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results in Nature Materials.

The animation above shows molecular building blocks joining the tip of a growing nanowire. Each block consists of a diamondoid – the smallest possible bit of diamond – attached to sulfur and copper atoms (yellow and brown spheres). Like LEGO blocks, they only fit together in certain ways that are determined by their size and shape. The copper and sulfur atoms form a conductive wire in the middle, and the diamondoids form an insulating outer shell.

“What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. “The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go.”


Fuzzy white clusters of nanowires on a lab bench, with a penny for scale.
Image Source – Hao Yan/SIMES; photo by SLAC National Accelerator Laboratory
In the image above, assembled with the help of diamondoids, the microscopic nanowires can be seen with the naked eye because the strong mutual attraction between their diamondoid shells makes them clump together, in this case by the millions. Also, at top right, is an image made with a scanning electron microscope shows nanowire clusters magnified 10,000 times.


Related articles

There are other methods to get materials to self-assemble, but this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.

Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets.

The needle-like wires have a semiconducting core – a combination of copper and sulfur known as a chalcogenide – surrounded by the attached diamondoids, which form an insulating shell.

The wires minuscule size is important, Melosh said, because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control.

“You can imagine weaving those into fabrics to generate energy,” Melosh said. “This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.”




Read Genesis Nanotech Online ~ Stanford team demonstrates a graphene-based thermal-to-electricity conversion technology + More News


Global Nano II 041316 41hQZPuT5NL._SX298_BO1,204,203,200_


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Read All The News Here: Genesis Nanotech: “Great Things from Small Things”

What Do You Think About Nanotechnology? Tell Us with Our Quick Survey – Pleeez!


Slate Nanotechnology Survey

Slate has recently published an online survey “Tell Us What You Think About Nanotechnology” (Follow the link above to take that survey).

Which … got us to thinking. “We” (Team GNT) should have our very own Survey on Nanotechnology with more focus on youOUR READERS!

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So … we are asking you to share your comments with us by answering a few questions and also … leaving us any ‘Open Comments’ you would care to leave. We will gather your responses, share the most interesting ones and let you know what others are “thinking and saying” about Nanotechnology. 


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Stanford U. – Iron nanoparticles make immune cells attack cancer

ironnanopartA mouse study found that ferumoxytol prompts immune cells called tumor-associated macrophages to destroy tumor cells. Credit: Amy Thomas

Stanford researchers accidentally discovered that iron nanoparticles invented for anemia treatment have another use: triggering the immune system’s ability to destroy tumor cells.

Iron  can activate the immune system to attack , according to a study led by researchers at the Stanford University School of Medicine.

The nanoparticles, which are commercially available as the injectable iron supplement ferumoxytol, are approved by the Food and Drug Administration to treat .

The mouse study found that ferumoxytol prompts immune cells called tumor-associated macrophages to destroy cancer cells, suggesting that the nanoparticles could complement existing cancer treatments. The discovery, described in a paper published online Sept. 26 in Nature Nanotechnology, was made by accident while testing whether the nanoparticles could serve as Trojan horses by sneaking chemotherapy into tumors in mice.

“It was really surprising to us that the nanoparticles activated macrophages so that they started to attack cancer cells in mice,” said Heike Daldrup-Link, MD, who is the study’s senior author and an associate professor of radiology at the School of Medicine. “We think this concept should hold in human patients, too.”

Daldrup-Link’s team conducted an experiment that used three groups of mice: an experimental group that got nanoparticles loaded with chemo, a control group that got nanoparticles without chemo and a control group that got neither. The researchers made the unexpected observation that the growth of the tumors in control animals that got nanoparticles only was suppressed compared with the other controls.

Getting macrophages back on track

The researchers conducted a series of follow-up tests to characterize what was happening. Experimenting with cells in a dish, they showed that called tumor-associated macrophages were required for the nanoparticles’ anti-cancer activity; in cell cultures without macrophages, the iron nanoparticles had no effect against cancer cells.

Before this study was done, it was already known that in healthy people, tumor-associated macrophages detect and eat individual tumor cells. However, large tumors can hijack the tumor-associated macrophages, causing them to stop attacking and instead begin secreting factors that promote the cancer’s growth.

The study showed that the iron nanoparticles switch the macrophages back to their cancer-attacking state, as evidenced by tracking the products of the macrophages’ metabolism and examining their patterns of gene expression.

Furthermore, in a of breast cancer, the researchers demonstrated that the ferumoxytol inhibited tumor growth when given in doses, adjusted for body weight, similar to those approved by the FDA for anemia treatment. Prior studies had shown that the nanoparticles are metabolized over a period of about six weeks, and the new study showed that the anti-cancer effect of a single dose of nanoparticles declined over about three weeks.

The scientists also tested whether the nanoparticles could stop cancer from spreading. In a mouse model of small-cell lung cancer, the nanoparticles reduced tumor formation in the liver, a common site of metastasis in both mice and humans. In a separate model of liver metastasis, pretreatment with nanoparticles before tumor cells were introduced greatly reduced the volume of liver tumors.

Potential clinical applications

The study’s results suggest several possible applications to test in human trials, Daldrup-Link said. For instance, after surgery to remove a potentially metastatic tumor, patients often need chemotherapy but must wait until they recover from the operation to tolerate the severe side effects of conventional chemo. The iron nanoparticles lack the toxic side effects of chemotherapy, suggesting they might be given to patients during the surgical recovery period.

“We think this could bridge the time when the patient is quite sick after surgery, and help keep the cancer from spreading until they are able to receive chemotherapy,” said Daldrup-Link.

The nanoparticles may also help cancer patients whose tumors can’t be completely removed. “If there are some left after surgery, the situation that cancer surgeons call positive margins, we think it might work to inject iron nanoparticles there, and the smaller tumor seeds could potentially be taken care of by our immune system,” Daldrup-Link said.

The fact that the nanoparticles are already FDA-approved speeds the ability to test these applications in humans, she added.

The new findings will also help cancer researchers conduct more accurate evaluations of nanoparticle-drug combinations, Daldrup-Link said. “In many studies, researchers just consider nanoparticles as drug vehicles,” she said. “But they may have hidden intrinsic effects that we won’t appreciate unless we look at the nanoparticles themselves.”

Explore further: Nanoparticles target and kill cancer stem cells that drive tumor growth

More information: Iron oxide nanoparticles inhibit tumour growth by inducing pro-inflammatory macrophage polarization in tumour tissues, Nature Nanotechnology,


Stanford University: Flawed “nanodiamonds” could produce next-generation tools for imaging and communications

Diamonds Nano 051316 preciselyflaClose-up of purified diamondoids on a lab bench. Too small to see with the naked eye, diamondoids are visible only when they clump together in fine, sugar-like crystals like these.


Stanford and SLAC National Accelerator Laboratory jointly run the world’s leading program for isolating and studying diamondoids—the tiniest possible specks of diamond. Found naturally in petroleum fluids, these interlocking carbon cages weigh less than a billionth of a billionth of a carat (a carat weighs about the same as 12 grains of rice); the smallest ones contain just 10 atoms.

Over the past decade, a team led by two Stanford-SLAC faculty members—Nick Melosh, an associate professor of materials science and engineering and of photon science, and Zhi-Xun Shen, a professor of photon science and of physics and applied physics – has found potential roles for in improving , assembling materials and printing circuits on computer chips. The team’s work takes place within SIMES, the Stanford Institute for Materials and Energy Sciences, which is run jointly with SLAC.

Before they can do that, though, just getting the diamondoids is a technical feat. It starts at the nearby Chevron refinery in Richmond, California, with a railroad tank car full of crude oil from the Gulf of Mexico. “We analyzed more than a thousand oils from around the world to see which had the highest concentrations of diamondoids,” says Jeremy Dahl, who developed key diamondoid isolation techniques with fellow Chevron researcher Robert Carlson before both came to Stanford—Dahl as a physical science research associate and Carlson as a visiting scientist.

Precisely flawed nanodiamonds could produce next-generation tools for imaging and communications
Solutions containing diamondoids await purity analysis in a SLAC lab. Credit: Christopher Smith, SLAC National Accelerator Laboratory

The original isolation steps were carried out at the Chevron refinery, where the selected crudes were boiled in huge pots to concentrate the diamondoids. Some of the residue from that work came to a SLAC lab, where small batches are repeatedly boiled to evaporate and isolate molecules of specific weights. These fluids are then forced at high pressure through sophisticated filtration systems to separate out diamondoids of different sizes and shapes, each of which has different properties.

The diamondoids themselves are invisible to the eye; the only reason we can see them is that they clump together in fine, sugar-like crystals. “If you had a spoonful,” Dahl says, holding a few in his palm, “you could give 100 billion of them to every person on Earth and still have some left over.”

Recently, the team started using diamondoids to seed the growth of flawless, nano-sized diamonds in a lab at Stanford. By introducing other elements, such as silicon or nickel, during the growing process, they hope to make nanodiamonds with precisely tailored flaws that can produce single photons of light for next-generation optical communications and biological imaging.

Precisely flawed nanodiamonds could produce next-generation tools for imaging and communications
Jeremy Dahl holds clumps of diamondoid crystals. Credit: Christopher Smith, SLAC National Accelerator Laboratory

Early results show that the quality of optical materials grown from diamondoid seeds is consistently high, says Stanford’s Jelena Vuckovic, a professor of electrical engineering who is leading this part of the research with Steven Chu, professor of physics and of molecular and cellular physiology.

“Developing a reliable way of growing the nanodiamonds is critical,” says Vuckovic, who is also a member of Stanford Bio-X. “And it’s really great to have that source and the grower right here at Stanford. Our collaborators grow the material, we characterize it and we give them feedback right away. They can change whatever we want them to change.”

Precisely flawed nanodiamonds could produce next-generation tools for imaging and communications
Nano-scale diamondoid crystals, seen above, are derived from petroleum. They have potential for applications in energy, electronics, and molecular imaging. Credit: Nick Melosh

Explore further: Forces within molecules can strengthen extra-long carbon-carbon bonds


Stanford Precourt Institute for Energy Joins U.S. Department of Energy and MIT Energy Initiative Program to Advance Women’s Leadership in Clean Energy

C3E Womens Energy 20130809-c3e-videoThe U.S. Department of Energy (DOE) has announced that the Precourt Institute for Energy at Stanford University is joining the Massachusetts Institute of Technology Energy Initiative (MITEI) to support implementation of the DOE-led U.S. Clean Energy Education & Empowerment (C3E) program to advance women’s participation and leadership in clean energy.

Women represent substantially less than half of the workforce across the energy field; closing the gender gap is a major goal of C3E. The new collaboration with the Stanford Precourt Institute for Energy will broaden the geographic reach of the U.S. C3E program and help further raise awareness of C3E and women’s leadership in the energy sector.

The U.S. C3E program includes C3E Ambassadors, senior leaders who act as role models and advocates for women in clean energy, and an online community for women in energy called The U.S. C3E program also holds an annual C3E Women in Clean Energy Symposium designed to help women in the clean energy sector build the skills and professional networks needed to succeed. Many participants say that the symposium inspired them to take the next step in their careers, whether taking on a new leadership role or starting a clean energy business.

Each symposium features winners of the C3E Awards, which recognize the outstanding leadership and achievements of mid-career women working to advance clean energy. C3E Awards are offered in eight categories: Advocacy, Business, Education, Entrepreneurship, Government, International, Law & Finance, and Research. Nominations for the 2016 C3E Awards are currently open, with submissions due by January 8, 2016 at

Over the past four years, DOE and MITEI have collaborated on the planning and implementation of the annual awards program and symposium. That responsibility will now be shared with the Stanford Precourt Institute for Energy, which will host the event on a rotating basis. The fifth annual symposium will be held at Stanford University in May 2016, and the sixth symposium will be at MIT in 2017. This year, awardees will also be recognized at the Seventh Clean Energy Ministerial hosted by the United States in San Francisco on June 1-2, 2016.

About C3E and the U.S. C3E Program

The international C3E initiative was launched by the Clean Energy Ministerial (CEM) in 2010. The C3E initiative was born out of recognition that the ideas and talents of all members of society are essential to meeting our future clean energy challenges. The U.S. C3E program is part of the CEM’s C3E initiative. Additional information is available at and

About U.S. Department of Energy

The DOE mission is to ensure America’s security and prosperity by addressing its energy, environmental, and nuclear challenges through transformative science and technology solutions. DOE coordinates the Clean Energy Ministerial, a 24-government forum to drive the transition to a global clean energy economy. DOE leads the C3E initiative along with several other initiatives under the auspices of the Clean Energy Ministerial. Additional information is available at

About MIT Energy Initiative

The MIT Energy Initiative (MITEI) is MIT’s hub for energy research, education, and outreach. MITEI links science, policy, and innovation to develop technologies and solutions that deliver clean, affordable, and plentiful sources of energy. Founded in 2006, MITEI’s mission is to facilitate low- and no-carbon solutions that will efficiently meet global energy needs while minimizing environmental impacts and mitigating climate change. MITEI is proud to support programs that increase and showcase diversity in the energy field, including the U.S. C3E program. Approximately one-third of MIT faculty engages in energy-related classes or research. Additional information is available at

About Stanford Precourt Institute for Energy

Stanford faculty and students are committed to making the world’s energy systems less vulnerable to economic, security, and environmental threats, and more capable of delivering modern energy services to the billions of people who lack them. The Stanford Precourt Institute for Energy supports and integrates the full spectrum of energy research and education, from basic science and technology to policy and business. The institute also cultivates alliances with industry, governments, civic organizations, and other research institutions to ensure that Stanford researchers and students help invent the energy future we seek. The institute values diversity and is pleased to support the U.S. C3E program. Additional information is available at

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

MIT Desal Shock 111315 bt1511_MIT-fracking-pondAs the availability of clean, potable water becomes an increasingly urgent issue in many parts of the world, researchers are searching for new ways to treat salty, brackish or contaminated water to make it usable. Now a team at MIT has come up with an innovative approach that, unlike most traditional desalination systems, does not separate ions or water molecules with filters, which can become clogged, or boiling, which consumes great amounts of energy.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Source: Massachusetts Institute of Technology


Stanford: Team claims to have created a sample of Stanene – So What? What About ZERO Loss to Due to Heat in Electronics

Staenne 55c20c36ce5cdA team of researchers with members from Stanford University and several institutions in China is claiming to have found a way to create a sample of stanene—a one-atom thick mesh (buckled honeycomb) of tin that theories have predicted could be used to conduct electricity with zero loss due to heat. In their paper published in the journal Nature Materials, the team describes the process they used to create their sample and the problems they encountered when trying to test its conductivity.

Graphene has been in the news a lot of late, as scientists have found many uses for it—the one-atom thick sheets of carbon have excellent electrical (and other) properties. But even as research with graphene continues, other scientists have been looking for a way to create stanene (which was predicted to possibly exist just two years ago) because it is believed it could be used to drastically improve the process by which electricity is used in electronics. Electrons, it is believed could travel through the material at without bumping into other electrons, as occurs with other materials, causing vibrations, resulting in heat—and loss of energy from the medium. With stanene, the electrons would travel along just the edges of the mesh—it could not get into the center because of properties—making it a . If theories about stanene turn out to be true, wires could be made that would carry great distances from a source to a destination without energy losses, for example, or phones and their chargers could operate without getting hot.

To make their sample, the researchers vaporized a bit of tin inside of a vacuum chamber allowing it to form its characteristic mesh on a bismuth telluride surface. The team was able to see only the top ridges of the structure with a scanning tunneling microscope, however and believe the substrate interacted with the mesh, preventing conductivity testing. In order to get a better view, the team acknowledges that they will have to create a bigger sample. Others have already suggested that it might be possible to confirm the structure of the material using X-ray diffraction.

Explore further: Will 2-D tin be the next super material?

More information: Epitaxial growth of two-dimensional stanene, Nature Materials (2015) DOI: 10.1038/nmat4384

Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.