Category Archives: energy

Want better energy storage materials? Add salt

An April 22, 2016 news item on Nanowerk reveals a secret to better energy storage materials,

The secret to making the best energy storage materials is growing them with as much surface area as possible. Like baking, it requires just the right mixture of ingredients prepared in a specific amount and order at just the right temperature to produce a thin sheet of material with the perfect chemical consistency to be useful for storing energy. A team of researchers from Drexel University, Huazhong University of Science and Technology (HUST) and Tsinghua University recently discovered a way to improve the recipe and make the resulting materials bigger and better and soaking up energy — the secret? Just add salt.

An April 22, 2016 Drexel University news release (also on EurekAlert), which originated the news item, provides more detail,

The team’s findings, which were recently published in the journal Nature Communications, show that using salt crystals as a template to grow thin sheets of conductive metal oxides make the materials turn out larger and more chemically pure — which makes them better suited for gathering ions and storing energy.

“The challenge of producing a metal oxide that reaches theoretical performance values is that the methods for making it inherently limit its size and often foul its chemical purity, which makes it fall short of predicted energy storage performance,” said Jun Zhou, a professor at HUST’s Wuhan National Laboratory for Optoelectronics and an author of the research. Our research reveals a way to grow stable oxide sheets with less fouling that are on the order of several hundreds of times larger than the ones that are currently being fabricated.”

In an energy storage device — a battery or a capacitor, for example — energy is contained in the chemical transfer of ions from an electrolyte solution to thin layers of conductive materials. As these devices evolve they’re becoming smaller and capable of holding an electric charge for longer periods of time without needing a recharge. The reason for their improvement is that researchers are fabricating materials that are better equipped, structurally and chemically, for collecting and disbursing ions.

In theory, the best materials for the job should be thin sheets of metal oxides, because their chemical structure and high surface area makes it easy for ions to attach — which is how energy storage occurs. But the metal oxide sheets that have been fabricated in labs thus far have fallen well short of their theoretical capabilities.

According to Zhou, Tang [?] and the team from HUST, the problem lies in the process of making the nanosheets — which involves either a deposition from gas or a chemical etching — often leaves trace chemical residues that contaminate the material and prevent ions from bonding to it. In addition, the materials made in this way are often just a few square micrometers in size.

Using salt crystals as a substrate for growing the crystals lets them spread out and form a larger sheet of oxide material. Think of it like making a waffle by dripping batter into a pan versus pouring it into a big waffle iron; the key to getting a big, sturdy product is getting the solution — be it batter, or chemical compound — to spread evenly over the template and stabilize in a uniform way.

“This method of synthesis, called ‘templating’ — where we use a sacrificial material as a substrate for growing a crystal — is used to create a certain shape or structure,” said Yury Gogotsi, PhD, University and Trustee Chair professor in Drexel’s College of Engineering and head of the A.J. Drexel Nanomaterials Institute, who was an author of the paper. “The trick in this work is that the crystal structure of salt must match the crystal structure of the oxide, otherwise it will form an amorphous film of oxide rather than a thing, strong and stable nanocrystal. This is the key finding of our research — it means that different salts must be used to produce different oxides.”

Researchers have used a variety of chemicals, compounds, polymers and objects as growth templates for nanomaterials. But this discovery shows the importance of matching a template to the structure of the material being grown. Salt crystals turn out to be the perfect substrate for growing oxide sheets of magnesium, molybdenum and tungsten.

The precursor solution coats the sides of the salt crystals as the oxides begin to form. After they’ve solidified, the salt is dissolved in a wash, leaving nanometer-thin two-dimensional sheets that formed on the sides of the salt crystal — and little trace of any contaminants that might hinder their energy storage performance. By making oxide nanosheets in this way, the only factors that limit their growth is the size of the salt crystal and the amount of precursor solution used.

“Lateral growth of the 2D oxides was guided by salt crystal geometry and promoted by lattice matching and the thickness was restrained by the raw material supply. The dimensions of the salt crystals are tens of micrometers and guide the growth of the 2D oxide to a similar size,” the researchers write in the paper. “On the basis of the naturally non-layered crystal structures of these oxides, the suitability of salt-assisted templating as a general method for synthesis of 2D oxides has been convincingly demonstrated.”

As predicted, the larger size of the oxide sheets also equated to a greater ability to collect and disburse ions from an electrolyte solution — the ultimate test for its potential to be used in energy storage devices. Results reported in the paper suggest that use of these materials may help in creating an aluminum-ion battery that could store more charge than the best lithium-ion batteries found in laptops and mobile devices today.

Gogotsi, along with his students in the Department of Materials Science and Engineering, has been collaborating with Huazhong University of Science and Technology since 2012 to explore a wide variety of materials for energy storage application. The lead author of the Nature Communications article, Xu Xiao, and co-author Tiangi Li, both Zhou’s doctoral students, came to Drexel as exchange students to learn about the University’s supercapacitor research. Those visits started a collaboration, which was supported by Gogotsi’s annual trips to HUST. While the partnership has already yielded five joint publications, Gogotsi speculates that this work is only beginning.

“The most significant result of this work thus far is that we’ve demonstrated the ability to generate high-quality 2D oxides with various compositions,” Gogotsi said. “I can certainly see expanding this approach to other oxides that may offer attractive properties for electrical energy storage, water desalination membranes, photocatalysis and other applications.”

Here’s a link to and a citation for the paper,

Scalable salt-templated synthesis of two-dimensional transition metal oxides by Xu Xiao, Huaibing Song, Shizhe Lin, Ying Zhou, Xiaojun Zhan, Zhimi Hu, Qi Zhang, Jiyu Sun, Bo Yang, Tianqi Li, Liying Jiao, Jun Zhou, Jiang Tang, & Yury Gogotsi. Nature Communications 7, Article number:  11296 doi:10.1038/ncomms11296 Published 22 April 2016

This is an open access paper.

Transparent wood instead of glass for window panes?

The transparent wood is made by removing the lignin in the wood veneer. (Photo: Peter Larsson

The transparent wood is made by removing the lignin in the wood veneer. (Photo: Peter Larsson

Not quite ready as a replacement for some types of glass window panes, nonetheless, transparent (more like translucent) wood is an impressive achievement. According to a March 30, 2016 news item on ScienceDaily size is what makes this piece of transparent wood newsworthy,

Windows and solar panels in the future could be made from one of the best — and cheapest — construction materials known: wood. Researchers at Stockholm’s KTH Royal Institute of Technology [Sweden] have developed a new transparent wood material that’s suitable for mass production.

Lars Berglund, a professor at Wallenberg Wood Science Center at KTH, says that while optically transparent wood has been developed for microscopic samples in the study of wood anatomy, the KTH project introduces a way to use the material on a large scale. …

A March 31 (?), 2016 KTH Institute of Technology press release, which originated the news item, provides more detail,

“Transparent wood is a good material for solar cells, since it’s a low-cost, readily available and renewable resource,” Berglund says. “This becomes particularly important in covering large surfaces with solar cells.”

Berglund says transparent wood panels can also be used for windows, and semitransparent facades, when the idea is to let light in but maintain privacy.

The optically transparent wood is a type of wood veneer in which the lignin, a component of the cell walls, is removed chemically.

“When the lignin is removed, the wood becomes beautifully white. But because wood isn’t not naturally transparent, we achieve that effect with some nanoscale tailoring,” he says.

The white porous veneer substrate is impregnated with a transparent polymer and the optical properties of the two are then matched, he says.

“No one has previously considered the possibility of creating larger transparent structures for use as solar cells and in buildings,” he says

Among the work to be done next is enhancing the transparency of the material and scaling up the manufacturing process, Berglund says.

“We also intend to work further with different types of wood,” he adds.

“Wood is by far the most used bio-based material in buildings. It’s attractive that the material comes from renewable sources. It also offers excellent mechanical properties, including strength, toughness, low density and low thermal conductivity.”

The American Chemical Society has a March 30, 2016 news release about the KTH achievement on EurekAlert  highlighting another potential use for transparent wood,

When it comes to indoor lighting, nothing beats the sun’s rays streaming in through windows. Soon, that natural light could be shining through walls, too. Scientists have developed transparent wood that could be used in building materials and could help home and building owners save money on their artificial lighting costs. …

Homeowners often search for ways to brighten up their living space. They opt for light-colored paints, mirrors and lots of lamps and ceiling lights. But if the walls themselves were transparent, this would reduce the need for artificial lighting — and the associated energy costs. Recent work on making transparent paper from wood has led to the potential for making similar but stronger materials. Lars Berglund and colleagues wanted to pursue this possibility.

Here’s a link to and a citation for the paper,

Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance by Yuanyuan Li, Qiliang Fu, Shun Yu, Min Yan, and Lars Berglund. Biomacromolecules, Article ASAP DOI: 10.1021/acs.biomac.6b00145 Publication Date (Web): March 4, 2016

Copyright © 2016 American Chemical Society

This paper appears to be open access.

Split some water molecules and save solar and wind (energy) for a future day

Professor Ted Sargent’s research team at the University of Toronto has a developed a new technique for saving the energy harvested by sun and wind farms according to a March 28, 2016 news item on Nanotechnology Now,

We can’t control when the wind blows and when the sun shines, so finding efficient ways to store energy from alternative sources remains an urgent research problem. Now, a group of researchers led by Professor Ted Sargent at the University of Toronto’s Faculty of Applied Science & Engineering may have a solution inspired by nature.

The team has designed the most efficient catalyst for storing energy in chemical form, by splitting water into hydrogen and oxygen, just like plants do during photosynthesis. Oxygen is released harmlessly into the atmosphere, and hydrogen, as H2, can be converted back into energy using hydrogen fuel cells.

Discovering a better way of storing energy from solar and wind farms is “one of the grand challenges in this field,” Ted Sargent says (photo above by Megan Rosenbloom via flickr) Courtesy: University of Toronto

Discovering a better way of storing energy from solar and wind farms is “one of the grand challenges in this field,” Ted Sargent says (photo above by Megan Rosenbloom via flickr) Courtesy: University of Toronto

A March 24, 2016 University of Toronto news release by Marit Mitchell, which originated the news item, expands on the theme,

“Today on a solar farm or a wind farm, storage is typically provided with batteries. But batteries are expensive, and can typically only store a fixed amount of energy,” says Sargent. “That’s why discovering a more efficient and highly scalable means of storing energy generated by renewables is one of the grand challenges in this field.”

You may have seen the popular high-school science demonstration where the teacher splits water into its component elements, hydrogen and oxygen, by running electricity through it. Today this requires so much electrical input that it’s impractical to store energy this way — too great proportion of the energy generated is lost in the process of storing it.

This new catalyst facilitates the oxygen-evolution portion of the chemical reaction, making the conversion from H2O into O2 and H2 more energy-efficient than ever before. The intrinsic efficiency of the new catalyst material is over three times more efficient than the best state-of-the-art catalyst.

Details are offered in the news release,

The new catalyst is made of abundant and low-cost metals tungsten, iron and cobalt, which are much less expensive than state-of-the-art catalysts based on precious metals. It showed no signs of degradation over more than 500 hours of continuous activity, unlike other efficient but short-lived catalysts. …

“With the aid of theoretical predictions, we became convinced that including tungsten could lead to a better oxygen-evolving catalyst. Unfortunately, prior work did not show how to mix tungsten homogeneously with the active metals such as iron and cobalt,” says one of the study’s lead authors, Dr. Bo Zhang … .

“We invented a new way to distribute the catalyst homogenously in a gel, and as a result built a device that works incredibly efficiently and robustly.”

This research united engineers, chemists, materials scientists, mathematicians, physicists, and computer scientists across three countries. A chief partner in this joint theoretical-experimental studies was a leading team of theorists at Stanford University and SLAC National Accelerator Laboratory under the leadership of Dr. Aleksandra Vojvodic. The international collaboration included researchers at East China University of Science & Technology, Tianjin University, Brookhaven National Laboratory, Canadian Light Source and the Beijing Synchrotron Radiation Facility.

“The team developed a new materials synthesis strategy to mix multiple metals homogeneously — thereby overcoming the propensity of multi-metal mixtures to separate into distinct phases,” said Jeffrey C. Grossman, the Morton and Claire Goulder and Family Professor in Environmental Systems at Massachusetts Institute of Technology. “This work impressively highlights the power of tightly coupled computational materials science with advanced experimental techniques, and sets a high bar for such a combined approach. It opens new avenues to speed progress in efficient materials for energy conversion and storage.”

“This work demonstrates the utility of using theory to guide the development of improved water-oxidation catalysts for further advances in the field of solar fuels,” said Gary Brudvig, a professor in the Department of Chemistry at Yale University and director of the Yale Energy Sciences Institute.

“The intensive research by the Sargent group in the University of Toronto led to the discovery of oxy-hydroxide materials that exhibit electrochemically induced oxygen evolution at the lowest overpotential and show no degradation,” said University Professor Gabor A. Somorjai of the University of California, Berkeley, a leader in this field. “The authors should be complimented on the combined experimental and theoretical studies that led to this very important finding.”

Here’s a link to and a citation for the paper,

Homogeneously dispersed, multimetal oxygen-evolving catalysts by Bo Zhang, Xueli Zheng, Oleksandr Voznyy, Riccardo Comin, Michal Bajdich, Max García-Melchor, Lili Han, Jixian Xu, Min Liu, Lirong Zheng, F. Pelayo García de Arquer, Cao Thang Dinh, Fengjia Fan, Mingjian Yuan, Emre Yassitepe, Ning Chen, Tom Regier, Pengfei Liu, Yuhang Li, Phil De Luna, Alyf Janmohamed, Huolin L. Xin, Huagui Yang, Aleksandra Vojvodic, Edward H. Sargent. Science  24 Mar 2016: DOI: 10.1126/science.aaf1525

This paper is behind a paywall.

Tune your windows for privacy

Caption: With an applied voltage, the nanowires on either side of the glass become attracted to each other and move toward each other, squeezing and deforming the soft elastomer. Because the nanowires are scattered unevenly across the surface, the elastomer deforms unevenly. That uneven roughness causes light to scatter, turning the glass opaque. Credit: David Clarke/Harvard SEAS [School of Engineering and Applied Sciences]

Right now, this is my favourite science illustration. A March 14, 2016 news item on Nanowerk announces Harvard’s new technology that can turn a clear window into an opaque one at the touch of a switch,

Say goodbye to blinds.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a technique that can quickly change the opacity of a window, turning it cloudy, clear or somewhere in between with the flick of a switch.

Tunable windows aren’t new but most previous technologies have relied on electrochemical reactions achieved through expensive manufacturing. This technology, developed by David Clarke, the Extended Tarr Family Professor of Materials, and postdoctoral fellow Samuel Shian, uses geometry [to] adjust the transparency of a window.

A March 14, 2016 Harvard University news release (also on EurekAlert) by Leah Burrows, which originated the news item, describes the technology in more detail,

The tunable window is comprised of a sheet of glass or plastic, sandwiched between transparent, soft elastomers sprayed with a coating of silver nanowires, too small to scatter light on their own.

But apply an electric voltage and things change quickly.

With an applied voltage, the nanowires on either side of the glass are energized to move toward each other, squeezing and deforming the soft elastomer. Because the nanowires are distributed unevenly across the surface, the elastomer deforms unevenly. The resulting uneven roughness causes light to scatter, turning the glass opaque.

The change happens in less than a second.

It’s like a frozen pond, said Shian.

“If the frozen pond is smooth, you can see through the ice. But if the ice is heavily scratched, you can’t see through,” said Shian.

Clarke and Shian found that the roughness of the elastomer surface depended on the voltage, so if you wanted a window that is only light clouded, you would apply less voltage than if you wanted a totally opaque window.

“Because this is a physical phenomenon rather than based on a chemical reaction, it is a simpler and potentially cheaper way to achieve commercial tunable windows,” said Clarke.

Current chemical-based controllable windows use vacuum deposition to coat the glass, a process that deposits layers of a material molecule by molecule. It’s expensive and painstaking. In Clarke and Shian’s method, the nanowire layer can be sprayed or peeled onto the elastomer, making the technology scalable for larger architectural projects.

Next the team is working on incorporating thinner elastomers, which would require lower voltages, more suited for standard electronical supplies.

Here’s a link to and a citation for the paper,

Electrically tunable window device by Samuel Shian and David R. Clarke. Optics Letters Vol. 41, Issue 6, pp. 1289-1292 (2016) •doi: 10.1364/OL.41.001289

This is an open access paper.

Unboiling egg technology can cut through carbon nanotubes

One of 2015’s big science stories, Flinders University’s ‘egg unboiler’ (also known as, a vortex fluidic device). has made the news again in a March 11, 2016 news item on,

Technology used by scientists to unboil an egg is being adapted to precisely cut through carbon nanotubes used in solar panel manufacturing and cancer treatment.

Scientists from Flinders University in South Australia have proven their Vortex Fluidic Device’s ability to slice through carbon nanotubes with great precision.

A March 11, 2016 story written by Caleb Radford for The Lead, which originated the news item, notes the advantages to using this technology for slicing carbon nanotubes (CNTs) and prospects for commercialization,

Device creator and Flinders University Professor Colin Raston said the carbon nanotubes could be commercialised within 12 months.

“Importantly for this technology is that we have uniformity in products,” he said.

“It opens it up for applications in drug delivery if you can get all of the carbon nanotubes to about 100 nanometres … 100 nanometres is the ideal length for getting into tumours so you can actually functionalise them to target cancer cells.

“Uniformity in products also means that you can improve the solar cell efficiency in solar cell devices.”

Flinders University scientists last year were awarded an Ig Nobel Award for creating the Vortex Fluidic Device and using it to unboil an egg.

The device can also be used to slice CNTs accurately to an average length of 170 nanometres using only water, a solvent and a laser.

It is also a simpler and cheaper process than previous methods, which resulted in random lengths that made it difficult to deliver drugs to patients and transfer electrons for solar panel manufacturing.

Flinders University PhD student Kasturi Vimalanathan, who played a key role in discovering new applications for the device, said the machines ability to cut carbon nanotubes to a similar length significantly increased the efficiency of solar cells.

“They shorten the carbon nanotubes to fit in all the chemicals so it can withstand high temperatures,” she said.

“It increases the efficiency and enhances the photoelectric conversion because they can provide a shorter transportation pathway for these electrons.

“It’s a one step method we can scale up. We can see cheaper solar panels on the back of this development.”

Here’s an image of Ralston, presumably with his Vortex Fluidic Device,

Professor Colin Raston received global attention and won an Ig Nobel prize on his way to becoming one of the biggest science stories of 2015. Courtesy Flinders University, Australia

Professor Colin Raston received global attention and won an Ig Nobel prize on his way to becoming one of the biggest science stories of 2015. Courtesy Flinders University, Australia

A Dec. 18, 2015 Flinders University blog posting announced Ralston’s Ig Nobel,

When Flinders University’s Professor Colin Raston unboiled an egg earlier this year with his ‘Vortex Fluidic Device’, in a feat previously considered impossible by science, he made TV screens and front pages all over the world, generating a veritable tsunami of ‘eggscellent’ puns.

The global impact of his achievement transformed the softly spoken South Australia Premier’s Professorial Research Fellow in Clean Technology into an internationally recognised figure overnight – and culminated in him receiving a prestigious Ig Nobel prize in September [2015].

In recognition of the massive amount of attention Professor Raston’s achievement received for Australian research, it has today been hailed as one of the top ten weird and wonderful Australian science stories of 2015 by the Australian Science and Media Centre (AusSMC).

Responding to the announcement, Professor Raston said he had been thrilled with the response to his achievement and had been ‘living the dream’ since.

“We were very interested in how the Vortex Fluidic Device might control protein folding, and the breakthrough with my collaborator at UCI, Greg Weiss, simplifies this, in a fraction of the time, minimising waste generation and energy usage. What this amounted to was unboiling an egg,” he said.

Who would have thought a device for unboiling eggs could be used to cut carbon nanotubes? Clearly, Kasturi Vimalanathan. Amazing.

For anyone interested and/or unfamiliar with the Ig Nobel prizes, there’s my Sept. 17, 2013 posting.

How vibrations affect nanoscale materials

A March 9, 2016 news item on ScienceDaily announces work concerning atomic vibrations,

All materials are made up of atoms, which vibrate. These vibrations, or ‘phonons’, are responsible, for example, for how electric charge and heat is transported in materials. Vibrations of metals, semiconductors, and insulators in are well studied; however, now materials are being nanosized to bring better performance to applications such as displays, sensors, batteries, and catalytic membranes. What happens to vibrations when a material is nanosized has until now not been understood.

A March 9, 2016 ETH Zurich press release (also on EurekAlert), which originated the news item, describes the world of vibration at the nanoscale and the potential impact this new information could have,

Soft Surfaces Vibrate Strongly

In a recent publication in Nature, ETH Professor Vanessa Wood and her colleagues explain what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications.

The paper shows that when materials are made smaller than about 10 to 20 nanometers – that is, 5,000 times thinner than a human air – the vibrations of the outermost atomic layers on surface of the nanoparticle are large and play an important role in how this material behaves.

“For some applications, like catalysis, thermoelectrics, or superconductivity, these large vibrations may be good, but for other applications like LEDs or solar cells, these vibrations are undesirable,” explains Wood.

Indeed, the paper explains why nanoparticle-based solar cells have until now not met their full promise.  The researchers showed using both experiment and theory that surface vibrations interact with electrons to reduce the photocurrent in solar cells.

“Now that we have proven that surface vibrations are important, we can systematically design materials to suppress or enhance these vibrations,” say Wood.

Improving Solar Cells

Wood’s research group has worked for a long time on a particular type of nanomaterial – colloidal nanocrystals – semiconductors with a diameter of 2 to 10 nanometers.  These materials are interesting because their optical and electrical properties are dependent on their size, which can be easily changed during their synthesis.

These materials are now used commercially as red- and green-light emitters in LED-based TVs and are being explored as possible materials for low cost, solution-processed solar cells.  Researchers have noticed that placing certain atoms around the surface of the nanocrystal can improve the performance of solar cells. The reason why this worked had not been understood.  The work published in the Nature paper now gives the answer:  a hard shell of atoms can suppress the vibrations and their interaction with electrons.  This means a higher photocurrent and a higher efficiency solar cell.

Big Science to Study the Nanoscale

Experiments were conducted in Professor Wood’s labs at ETH Zurich and at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. By observing how neutrons scatter off atoms in a material, it is possible to quantify how atoms in a material vibrate. To understand the neutron measurements, simulations of the atomic vibrations were run at the Swiss National Supercomputing Center (CSCS) in Lugano. Wood says, “without access to these large facilities, this work would not have been possible. We are incredibly fortunate here in Switzerland to have these world class facilities.”

The researchers have made available an image illustrating their work,

Vibrations of atoms in materials, the "phonons", are responsible for how electric charge and heat is transported in materials (Graphics: Deniz Bozyigit / ETH Zurich)

Vibrations of atoms in materials, the “phonons”, are responsible for how electric charge and heat is transported in materials (Graphics: Deniz Bozyigit / ETH Zurich)

Here’s a link to and a citation for the paper,

Soft surfaces of nanomaterials enable strong phonon interactions by Deniz Bozyigit, Nuri Yazdani, Maksym Yarema, Olesya Yarema, Weyde Matteo Mario Lin, Sebastian Volk, Kantawong Vuttivorakulchai, Mathieu Luisier, Fanni Juranyi, & Vanessa Wood. Nature (2016)  doi:10.1038/nature16977 Published online 09 March 2016

This paper is behind a paywall.

Solar cells and soap bubbles

The MIT team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. Photo: Joel Jean and Anna Osherov

The MIT team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. Photo: Joel Jean and Anna Osherov

That’s quite a compelling image and it comes to us courtesy of researchers at MIT (Massachusetts Institute of Technology). From a Feb. 25, 2016 MIT news release (also on EurekAlert),

Imagine solar cells so thin, flexible, and lightweight that they could be placed on almost any material or surface, including your hat, shirt, or smartphone, or even on a sheet of paper or a helium balloon.

Researchers at MIT have now demonstrated just such a technology: the thinnest, lightest solar cells ever produced. Though it may take years to develop into a commercial product, the laboratory proof-of-concept shows a new approach to making solar cells that could help power the next generation of portable electronic devices.

Bulović [Vladimir Bulović ], MIT’s associate dean for innovation and the Fariborz Maseeh (1990) Professor of Emerging Technology, says the key to the new approach is to make the solar cell, the substrate that supports it, and a protective overcoating to shield it from the environment, all in one process. The substrate is made in place and never needs to be handled, cleaned, or removed from the vacuum during fabrication, thus minimizing exposure to dust or other contaminants that could degrade the cell’s performance.

“The innovative step is the realization that you can grow the substrate at the same time as you grow the device,” Bulović says.

In this initial proof-of-concept experiment, the team used a common flexible polymer called parylene as both the substrate and the overcoating, and an organic material called DBP as the primary light-absorbing layer. Parylene is a commercially available plastic coating used widely to protect implanted biomedical devices and printed circuit boards from environmental damage. The entire process takes place in a vacuum chamber at room temperature and without the use of any solvents, unlike conventional solar-cell manufacturing, which requires high temperatures and harsh chemicals. In this case, both the substrate and the solar cell are “grown” using established vapor deposition techniques.

One process, many materials

The team emphasizes that these particular choices of materials were just examples, and that it is the in-line substrate manufacturing process that is the key innovation. Different materials could be used for the substrate and encapsulation layers, and different types of thin-film solar cell materials, including quantum dots or perovskites, could be substituted for the organic layers used in initial tests.

But already, the team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. The researchers acknowledge that this cell may be too thin to be practical — “If you breathe too hard, you might blow it away,” says Jean [Joel Jean, doctoral student] — but parylene films of thicknesses of up to 80 microns can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation.

A flexible parylene film, similar to kitchen cling-wrap but only one-tenth as thick, is first deposited on a sturdier carrier material – in this case, glass. Figuring out how to cleanly separate the thin material from the glass was a key challenge, explains Wang [Annie Wang, research scientist], who has spent many years working with parylene.

The researchers lift the entire parylene/solar cell/parylene stack off the carrier after the fabrication process is complete, using a frame made of flexible film. The final ultra-thin, flexible solar cells, including substrate and overcoating, are just one-fiftieth of the thickness of a human hair and one-thousandth of the thickness of equivalent cells on glass substrates — about two micrometers thick — yet they convert sunlight into electricity just as efficiently as their glass-based counterparts.

No miracles needed

“We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off,” explains Wang. Bulović says that like most new inventions, it all sounds very simple — once it’s been done. But actually developing the techniques to make the process work required years of effort.

While they used a glass carrier for their solar cells, Jean says “it could be something else. You could use almost any material,” since the processing takes place under such benign conditions. The substrate and solar cell could be deposited directly on fabric or paper, for example.

While the solar cell in this demonstration device is not especially efficient, because of its low weight, its power-to-weight ratio is among the highest ever achieved. That’s important for applications where weight is important, such as on spacecraft or on high-altitude helium balloons used for research. Whereas a typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15 watts of power per kilogram of weight, the new cells have already demonstrated an output of 6 watts per gram — about 400 times higher.

“It could be so light that you don’t even know it’s there, on your shirt or on your notebook,” Bulović says. “These cells could simply be an add-on to existing structures.”

Still, this is early, laboratory-scale work, and developing it into a manufacturable product will take time, the team says. Yet while commercial success in the short term may be uncertain, this work could open up new applications for solar power in the long term. “We have a proof-of-concept that works,” Bulović says. The next question is, “How many miracles does it take to make it scalable? We think it’s a lot of hard work ahead, but likely no miracles needed.”

Here’s a link to and a citation for the paper,

In situ vapor-deposited parylene substrates for ultra-thin, lightweight organic solar cells by Joel Jean, Annie Wang, Vladimir Bulović. Organic Electronics Volume 31, April 2016, Pages 120–126 doi:10.1016/j.orgel.2016.01.022

This paper is behind a paywall.

South Africa, energy, and nanotechnology

South African academics Nosipho Moloto, Associate Professor, Department of Chemistry, University of the Witwatersrand and Siyabonga P. Ngubane, Lecturer in Chemistry, University of the Witwatersrand have written a Feb. 17, 2016 article for The Conversation (also available on the South African Broadcasting Corporation website) about South Africa’s energy needs and its nanotechnology efforts (Note: Links have been removed),

Energy is an economic driver of both developed and developing countries. South Africa over the past few years has faced an energy crisis with rolling blackouts between 2008 and 2015. Part of the problem has been attributed to mismanagement by the state-owned utility company Eskom, particularly the shortcomings of maintenance plans on several plants.

But South Africa has two things going for it that could help it out of its current crisis. By developing a strong nanotechnology capability and applying this to its rich mineral reserves the country is well-placed to develop new energy technologies.

Nanotechnology has already shown that it has the potential to alleviate energy problems. …

It can also yield materials with new properties and the miniaturisation of devices. For example, since the discovery of graphene, a single atomic layer of graphite, several applications in biological engineering, electronics and composite materials have been identified. These include economic and efficient devices like solar cells and lithium ion secondary batteries.

Nanotechnology has seen an incredible increase in commercialisation. Nearly 10,000 patents have been filed by large corporations since its beginning in 1991. There are already a number of nanotechnology products and solutions on the market. Examples include Miller’s beer bottling composites, Armor’s N-Force line bulletproof vests and printed solar cells produced by Nanosolar – as well as Samsung’s nanotechnology television.

The advent of nanotechnology in South Africa began with the South African Nanotechnology Initiative in 2002. This was followed by the a [sic] national nanotechnology strategy in 2003.

The government has spent more than R450 million [Rand] in nanotechnology and nanosciences research since 2006. For example, two national innovation centres have been set up and funding has been made available for equipment. There has also been flagship funding.

The country could be globally competitive in this field due to the infancy of the technology. As such, there are plenty of opportunities to make novel discoveries in South Africa.

Mineral wealth

There is another major advantage South Africa has that could help diversify its energy supply. It has an abundance of mineral wealth with an estimated value of US$2.5 trillion. The country has the world’s largest reserves of manganese and platinum group metals. It also has massive reserves of gold, diamonds, chromite ore and vanadium.

Through beneficiation and nanotechnology these resources could be used to cater for the development of new energy technologies. Research in beneficiation of minerals for energy applications is gaining momentum. For example, Anglo American and the Department of Science and Technology have embarked on a partnership to convert hydrogen into electricity.

The Council for Scientific and Industrial research also aims to develop low cost lithium ion batteries and supercapacitors using locally mined manganese and titanium ores. There is collaborative researchto use minerals like gold to synthesize nanomaterials for application in photovoltaics.

The current photovoltaic market relies on importing solar cells or panels from Europe, Asia and the US for local assembly to produce arrays. South African UV index is one of the highest in the world which reduces the lifespan of solar panels. The key to a thriving and profitable photovoltaic sector therefore lies in local production and research and development to support the sector.

It’s worth reading the article in its entirety if you’re interested in a perspective on South Africa’s energy and nanotechnology efforts.

Turning sunlight into hydrogen (a Korean project)

A Feb. 17, 2016 news item on Nanowerk describes a new technique for solar water-splitting (turning sunlight into hydrogen),

A team of Korean researchers, affiliated with UNIST [Ulsan National Institute of Science and Technology] has recently pioneered in developing a new type of multilayered (Au NPs/TiO2/Au) photoelectrode that boosts the ability of solar water-splitting to produce hydrogen. According to the research team, this special photoelectrode, inspired by the way plants convert sunlight into energy is capable of absorbing visible light from the sun, and then using it to split water molecules (H2O) into hydrogen and oxygen.

A Feb. 1, 2016 UNIST news release, which originated the news item, expands on the theme,

This multilayered photoelectrode takes the form of two-dimensional hybrid metal-dielectric structure, which mainly consists of three layers of gold (Au) film, ultrathin TiO2 layer (20 nm), and gold nanoparticles (Au NPs). In a study, reported in the January 21, 2016 issue of Nano Energy, the team reported that this promising photoelectrode shows high light absorption of about 90% in the visible range 380–700 nm, as well as significant enhancement in photo-catalytic applications.

The researchers have made an image illustrating their work available,

Two-dimensional metastructured film with Titanium Oxide is fabricated as a photo-catalytic photoanode with exceptional visible light absorption. Courtesy: UNIST

Two-dimensional metastructured film with Titanium Oxide is fabricated as a photo-catalytic photoanode with exceptional visible light absorption. Courtesy: UNIST

Back to the news release,

Many structural designs, such as hierarchical and branched assemblies of nanoscale materials have been suggested to increase the UV-visible absorption and to enhance water-splitting efficiency. However, through incorporation of plasmonic metal nanoparticles (i.e. Au) to TiO2 structures, their photoelectrodes have shown to enhance the photoactivity in the entire UV-visible region of solar spectrum when compared with the existing ones, the team reports.

Prof. Jeong Min Baik of UNIST (School of Materials Science and Engineering) states, “Several attemps have been made to use UV-based photoelectrodes for hydrogen production, but this is the first time to use the metal-dielectric hybrid-structured film with TiO2 for oxygen production.” Moreover, according to Prof. Baik, this special type of photoelectrode uses approximately 95% of the visible spectrum of sunlight, which makes up a substantial portion (40%) of full sunlight. He adds, “The developed technology is expected to improve hydrogen production efficiency.”

Prof. Heon Lee (Korean University) states, “This metal-dielectric hybrid-structured film is expected to further reduce the overall cost of producing hydrogen, as it doesn’t require complex operation processes.” He continues by saying, “Using nanoimprint lithography, mass production of hydrogen will be soon possible.”

Prof. Baik adds, “This simple system may serve as an efficient platform for solar energy conversion, utilizing the whole UV-visible range of solar spectrum based on two-dimensional plasmonic photoelectrodes.”

Here’s a link to and a citation for the paper,

Two-dimensional metal-dielectric hybrid-structured film with titanium oxide for enhanced visible light absorption and photo-catalytic application by Joonmo Park, Hee Jun Kim, SangHyeon Nam, Hyowook Kim, Hak-Jong Choi, Youn Jeong Jang, Jae Sung Lee, Jonghwa Shin, Heon Lee, Jeong Min Baik. Nano Energy Volume 21, March 2016, Pages 115–122 doi:10.1016/j.nanoen.2016.01.004

This paper is behind a paywall.

University of British Columbia (Canada) researchers reverse coating process: a smart window story?

It’s nice to see that the science writing at the University of British Columbia (UBC) has gone up a notch if a Feb. 11, 2016 news release (original received via email; see also a Feb. 11, 2016 news item on Nanowerk and EurekAlert) is any indication,

Imagine if the picture window in your living room could double as a giant thermostat or big screen TV. A discovery by researchers at the University of British Columbia has brought us one step closer to this becoming a reality.

Researchers at UBC’s Okanagan campus in Kelowna found that coating small pieces of glass with extremely thin layers of metal like silver makes it possible to enhance the amount of light coming through the glass. This, coupled with the fact that metals naturally conduct electricity, may make it possible to add advanced technologies to windowpanes and other glass objects.

“Engineers are constantly trying to expand the scope of materials that they can use for display technologies, and having thin, inexpensive, see-through components that conduct electricity will be huge,” said UBC Associate Professor and lead investigator Kenneth Chau. “I think one of the most important implications of this research is the potential to integrate electronic capabilities into windows and make them smart.” [!]

The next phase of this research, added Chau, will be to incorporate their invention onto windows with an aim to selectively filter light and heat waves depending on the season or time of day.

The theory underlying the research was developed by Chau and collaborator Loïc Markley, an assistant professor of engineering at UBC. Chau and Markley questioned what would happen if they reversed the practice of applying glass over metal—a typical method used in the creation of energy efficient window coatings.

“It’s been known for quite a while that you could put glass on metal to make metal more transparent, but people have never put metal on top of glass to make glass more transparent,” said Markley. “It’s counter-intuitive to think that metal could be used to enhance light transmission, but we saw that this was actually possible, and our experiments are the first to prove it.”

This work from UBC comes on the heels of a University of Alberta team rethinking the architecture for thin film transistors  (a Feb. 10, 2016 posting).

Getting back to UBC, here’s a link to and a citation for the paper,

Layers by Coatings of Opposing Susceptibility: How Metals Help See Through Dielectrics by Mohammed Al Shakhs, Lucian Augusto, Loïc Markley, & Kenneth J. Chau. Scientific Reports 6, Article number: 20659 (2016) doi:10.1038/srep20659 Published online: 10 February 2016

This is an open access paper.

My most recent post about smart windows (a longstanding obsession) is a Jan. 21, 2016 piece featuring a UK technology that combines self-cleaning and temperature control properties for a possible market introduction in the next three to five years.