“Back to School” – Blue Bird is taking its new all-electric buses on the road to convince schools to go electric


Blue Bird, an important American bus manufacturer better known for its school buses, is taking its new electric buses on the road to school districts and fleet operators around the country to convince them to go electric.

The company unveiled their electric buses at the STN Tradeshow in Reno last year.

They made electric versions of their Type A, Type C, and Type D school buses – Type D pictured above.

Blue Bird says that both buses should be able to achieve about 100 to 120 miles of range, which is generally plenty for most school bus routes.

School buses generally operate on relatively short routes and they are often parked for long periods of time as they are not used as intensively as urban transit buses or coaches, which gives them opportunities to charge.

When unveiling the vehicles last year, Blue Bird said that the range was enabled by a massive 150 kWh battery pack, but now they have updated the powertrain with a new 160 kWh pack. The company said that a smaller 100 kWh option will also be made available for less demanding routes.

They are currently doing “Ride & Drive events” all around the country. They went to California, Nevada, Arizona, Colorado and Ohio.

Phil Horlock, president and CEO of Blue Bird Corporation:

After the outstanding response we saw in California, Blue Bird is excited to showcase our electric school buses to customers and drivers across North America, not as concept vehicles, but as a preview of our production buses later this fall. As both the pioneer and undisputed leader in alternative fuels, we are delighted to expand our “green” product offering by adding electric bus options in both Type C and D body styles. Our electric buses have received an Executive Order from the California Air Resources Board and both HVIP and TVIP listing, which qualify Blue Bird’s electric buses for grants available in California and New York, respectively. That’s great news for our customers and following our Ride & Drives in California, we are already receiving orders from school districts. We are open for business and taking orders!

They are currently in New York and then will head to Florida and later Ontario, Canada. You can follow their other events here.

According to the company, the first buses will be delivered at the end of the summer or early fall and they will deploy a Vehicle-to-Grid (V2G) feature – meaning that the buses could be used as energy storage systems – next year.

Electrek’s Take

I think all-electric school buses are a no-brainer since urban transit buses are already starting to be financially viable solutions and school buses don’t need nearly as much energy capacity in most cases.

Even if the upfront cost might be higher, they should be able to compensate it with fuel and maintenance savings.

In the case of Blue Bird, a Vehicle-to-Grid (V2G) feature is also a smart addition that could add value to school districts buying fleets since the buses are often parked for long periods of time and could be used as energy storage systems.

Lion, a Quebec-based school bus manufacturer, also offers an electric school bus option – not for Type D buses. Several other companies have now a few electric solutions, like Daimler’s first all-electric school bus, which is expected to enter production next year.

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3 Questions for Innovating the Clean Energy Economy (MIT Energy Initiative)


daniel-kammen-mit-energy-initiative-mitei-2018_0Daniel Kammen, professor of energy at the University of California at Berkeley, spoke on clean energy innovation and implementation in a talk at MIT. Photo: Francesca McCaffrey/MIT Energy Initiative

Daniel Kammen of the University of California at Berkeley discusses current efforts in clean energy innovation and implementation, and what’s coming next.

Daniel Kammen is a professor of energy at the University of California at Berkeley, with parallel appointments in the Energy and Resources Group (which he chairs), the Goldman School of Public Policy, and the Department of Nuclear Science and Engineering.

Recently, he gave a talk at MIT examining the current state of clean energy innovation and implementation, both in the U.S. and internationally. Using a combination of analytical and empirical approaches, he discussed the strengths and weaknesses of clean energy efforts on the household, city, and regional levels. The MIT Energy Initiative (MITEI) followed up with him on these topics.

Q: Your team has built energy transition models for several countries, including Chile, Nicaragua, China, and India. Can you describe how these models work and how they can inform global climate negotiations like the Paris Accords?

Clean Energy Storage I header1

A: My laboratory has worked with three governments to build open-source models of the current state of their energy systems and possible opportunities for improvement. This model, SWITCH , is an exceptionally high-resolution platform for examining the costs, reliability, and carbon emissions of energy systems as small as Nicaragua’s and as large as China’s. The exciting recent developments in the cost and performance improvements of solar, wind, energy storage, and electric vehicles permit the planning of dramatically decarbonized systems that have a wide range of ancillary benefits: increased reliability, improved air quality, and monetizing energy efficiency, to name just a few. With the Paris Climate Accords placing 80 percent or greater decarbonization targets on all nations’ agendas (sadly, except for the U.S. federal government), the need for an “honest broker” for the costs and operational issues around power systems is key.

Q: At the end of your talk, you mentioned a carbon footprint calculator that you helped create. How much do individual behaviors matter in addressing climate change?

A: The carbon footprint, or CoolClimate project, is a visualization and behavioral economics tool that can be used to highlight the impacts of individual decisions at the household, school, and city level. We have used it to support city-city competitions for “California’s coolest city,” to explore the relative impacts of lifetime choices (buying an electric vehicle versus or along with changes of diet), and more.

Q: You touched on the topic of the “high ambition coalition,” a 2015 United Nations Climate Change Conference goal of keeping warming under 1.5 degrees Celsius. Can you expand on this movement and the carbon negative strategies it would require?

A: As we look at paths to a sustainable global energy system, efforts to limit warming to 1.5 degrees Celsius will require not only zeroing out industrial and agricultural emissions, but also removing carbon from the atmosphere. This demands increasing natural carbon sinks by preserving or expanding forests, sustaining ocean systems, and making agriculture climate- and water-smart. One pathway, biomass energy with carbon capture and sequestration, has both supporters and detractors. It involves growing biomass, using it for energy, and then sequestering the emissions.

This talk was one in a series of MITEI seminars supported by IHS Markit.

MIT: Finding a New Way to Design and Analyze Better Battery Materials: Discoveries could accelerate the development of high-energy lithium batteries


Diagram illustrates the crystal lattice of a proposed battery electrolyte material called Li3PO4. The researchers found that measuring how vibrations of sound move through the lattice could reveal how well ions – electrically charged atoms or molecules – could travel through the solid material, and therefore how they would work in a real battery. In this diagram, the oxygen atoms are shown in red, the purple pyramid-like shapes are phosphate (PO4) molecules. The orange and green spheres are ions of lithium.
Image: Sokseiha Muy

Design principles could point to better electrolytes for next-generation lithium batteries.

A new approach to analyzing and designing new ion conductors — a key component of rechargeable batteries — could accelerate the development of high-energy lithium batteries and possibly other energy storage and delivery devices such as fuel cells, researchers say.

The new approach relies on understanding the way vibrations move through the crystal lattice of lithium ion conductors and correlating that with the way they inhibit ion migration. This provides a way to discover new materials with enhanced ion mobility, allowing rapid charging and discharging.

At the same time, the method can be used to reduce the material’s reactivity with the battery’s electrodes, which can shorten its useful life. These two characteristics — better ion mobility and low reactivity — have tended to be mutually exclusive.

The new concept was developed by a team led by W.M. Keck Professor of Energy Yang Shao-Horn, graduate student Sokseiha Muy, recent graduate John Bachman PhD ’17, and Research Scientist Livia Giordano, along with nine others at MIT, Oak Ridge National Laboratory, and institutions in Tokyo and Munich. Their findings were reported in the journal Energy and Environmental Science.

The new design principle has been about five years in the making, Shao-Horn says. The initial thinking started with the approach she and her group have used to understand and control catalysts for water splitting, and applying it to ion conduction — the process that lies at the heart of not only rechargeable batteries, but also other key technologies such as fuel cells and desalination systems.

While electrons, with their negative charge, flow from one pole of the battery to the other (thus providing power for devices), positive ions flow the other way, through an electrolyte, or ion conductor, sandwiched between those poles, to complete the flow.

Typically, that electrolyte is a liquid. A lithium salt dissolved in an organic liquid is a common electrolyte in today’s lithium-ion batteries. But that substance is flammable and has sometimes caused these batteries to catch fire. The search has been on for a solid material to replace it, which would eliminate that issue.

A variety of promising solid ion conductors exist, but none is stable when in contact with both the positive and negative electrodes in lithium-ion batteries, Shao-Horn says.

Therefore, seeking new solid ion conductors that have both high ion conductivity and stability is critical. But sorting through the many different structural families and compositions to find the most promising ones is a classic needle in a haystack problem. That’s where the new design principle comes in.

The idea is to find materials that have ion conductivity comparable to that of liquids, but with the long-term stability of solids. The team asked, “What is the fundamental principle? What are the design principles on a general structural level that govern the desired properties?” Shao-Horn says. A combination of theoretical analysis and experimental measurements has now yielded some answers, the researchers say.

“We realized that there are a lot of materials that could be discovered, but no understanding or common principle that allows us to rationalize the discovery process,” says Muy, the paper’s lead author. “We came up with an idea that could encapsulate our understanding and predict which materials would be among the best.”

The key was to look at the lattice properties of these solid materials’ crystalline structures. This governs how vibrations such as waves of heat and sound, known as phonons, pass through materials. This new way of looking at the structures turned out to allow accurate predictions of the materials’ actual properties. “Once you know [the vibrational frequency of a given material], you can use it to predict new chemistry or to explain experimental results,” Shao-Horn says.

The researchers observed a good correlation between the lattice properties determined using the model and the lithium ion conductor material’s conductivity. “We did some experiments to support this idea experimentally” and found the results matched well, she says.

They found, in particular, that the vibrational frequency of lithium itself can be fine-tuned by tweaking its lattice structure, using chemical substitution or dopants to subtly change the structural arrangement of atoms.

The new concept can now provide a powerful tool for developing new, better-performing materials that could lead to dramatic improvements in the amount of power that could be stored in a battery of a given size or weight, as well as improved safety, the researchers say.

Already, they used the method to find some promising candidates. And the techniques could also be adapted to analyze materials for other electrochemical processes such as solid-oxide fuel cells, membrane based desalination systems, or oxygen-generating reactions.

The team included Hao-Hsun Chang at MIT; Douglas Abernathy, Dipanshu Bansal, and Olivier Delaire at Oak Ridge; Santoshi Hori and Ryoji Kanno at Tokyo Institute of Technology; and Filippo Maglia, Saskia Lupart, and Peter Lamp at Research Battery Technology at BMW Group in Munich.

The work was supported by BMW, the National Science Foundation, and the U.S. Department of Energy.

Watch a YouTube Video on New Nano-Enabled Super Capacitors and Batteries

Research Focus: “BIG” Things Coming from Nanotechnology (very small things)


It may be a cliché, but in the world of nanotechnology, big things really do come in small packages.

The study and application of nanotechnology—science, engineering, and technology conducted at 1 to 100 nanometers—is rapidly growing across medicine, chemistry, physics, materials science, engineering and more.

According to the U.S. National Nanotechnology Initiative (NNI), nanotechnology as we now know it has only been around approximately 30 years. Despite the field’s relatively young lifespan, it has already made significant strides.

Today, researchers are developing everything from next-generation electronics to more effective drug delivery systems at the nanoscale. In February, R&D Magazine took a special focus on this up-and-coming area of research.

Electronics

We kicked off our nanotechnology coverage highlighting a new method to enhance the capabilities of the memristor—an emerging nanotechnology that offers a simpler and smaller alternative to the transistor. In our article, “Memristor Could Enable More Data Storage” we outlined a new memristor technology that can store up to 128 discernible memory states per switch, which is almost four times higher than what has been previously reported.

In another article, “Achieving Printed Power Electronics Means Going Beyond Silver Nanoparticles we outlined the limitations of 3D printed electronics using silver nanoparticle inks for systems that use high-current density known as “power electronics.” In the article, Greg Fritz, a material scientist in the Charles Stark Draper Laboratory, outlined the challenges with silver nanoparticle inks and his team’s research into alternative nano-layered materials for printing power electronics.

Expert contributor Ahmed A. Busnaina, the director of the Center for High-rate Nanomanufacturing (CHN) at Northeastern University, also shared an article outlining his research on nanoscale high-throughput printing technology. He explained a directed assembly-based printing processes developed by CHN in his article, “Scalable Printing Sensors and Electronics at the Nanoscale.”

In Researchers Use Tin Oxide Nanocrystals to Improve Battery Performance, we highlighted scientists at Washington State University’s School of Mechanical and Materials Engineering who utilized tin oxide nanocrystals to improve the performance of both sodium-ion and lithium-ion batteries.

Medicine

Nanotechnology is not limited to applications within traditional ‘technology.’ Nanoscale science also has a growing presence in the medical field, as nanomaterials are being formulated with conventional pharmaceutical agents to create more effective, safer, and more targeted drug delivery systems. We outlined the overall benefits of this approach in “Nanotechnology Can Improve Safety, Effectiveness in Drug Delivery.”The article highlights the work of the Center for Nanotechnology in Drug Delivery at the UNC Eshelman School of Pharmacy which is investigating nanotechnology to treat stroke, neurodegenerative and neurodevelopmental disorders, nerve agent and pesticide poisoning and other diseases and injuries.

One disease area at the forefront of nanomedicine is oncology. We spoke with Piotr Grodzinski, PhD, the Chief of Nanodelivery Systems and Devices Branch at the Cancer Imaging Program of the National Cancer Institute (NCI), to learn more about the role of nanotechnology in oncology for our article, Nanoparticle-Based Cancer Treatment: A Look at its Origins and What’s Next.” The first nanoparticle-based cancer treatment—a formulation of the chemotherapy agent doxorubicin delivered via the nanoparticle material liposome—was approved in 1995. Today, researchers are working on more complex innovations, such as nanoparticle combination therapies and nanoparticles for delivery of immunostimulatory or immunomodulatory molecules.

Material Science

Graphene—a 2D nanomaterial consisting of a single layer of carbon atoms arranged in a hexagonal lattice—has a host of applications. We highlighted one that could improve food safety in, New Lasing Method Enables Edible Graphene Food Trackers.” The article highlighted researchers from Rice University who had enhanced their laser-induced graphene technique to “write” graphene patterns onto food and other materials, enabling embed conductive identification tags and sensors onto products.

We also highlighted a way nanotechnology could be used to create a safer and cleaner environment in, Nano-Crystals Key to Continuously Self-Cleaning Surfaces.”  The article features New Clean NanoSeptic Self-Cleaning Surfaces—skins and mats that can be adhered to most any surface that utilize mineral nano-crystals to create an oxidation reaction stronger than bleach, without using poisons, heavy metals or chemicals. The nano-crystals, charged by visible light, act as a catalyst and the oxidation reaction breaks down organic material into base components including CO2, enabling the surface to continuously oxidize organic contaminants at the microscopic level.

Chemistry

Finally, we tackled the benefits of nanotechnology in the field of chemistry. In the article “Membrane Allows More Precise Chemical Separation Using Charged Nanochannels,” we highlighted a new type of filter has been designed to allow manufacturers to separate organic compounds not only by their size, but also by their electrostatic charge. The highly selective membrane filters could enable manufacturers to separate and purify chemicals in ways that are currently impossible, allowing them to potentially use less energy and cut carbon emissions.

Next Month’s Special Focus

Next month, R&D Magazine is focusing on technologies that are sustainable and clean, known as “green” technologies. Green technologies are created to mitigate or reverse the effects of human activity on the environment, providing a better future for all.

Check back in April for more on what’s happening within the green technology space in R&D.

Watch Our YouTube Video: Nano-Enabled Energy Storage: Super Capacitors and Batteries

The Coming Clean Disruption of Energy and Transportation: YouTube Video


Published on Jan 18, 2018

Mobility Disruption – A Presentation by Tony Seba, Silicon Valley Entrepreneur and Lecturer at Stanford University

The reinvention and connection between infrastructure and mobility will fundamentally disrupt the clean transport model.

It will change the way governments and consumers think about mobility, how power is delivered and consumed and the payment models for usage.

 Bold Predictions

“The industrial age of energy and transportation will be over by 2030. Maybe before.” – Tony Sena

Exponentially improving technologies such as solar, electric vehicles, and autonomous (self-driving) cars will disrupt and sweep away the energy and transportation industries as we know it.

The same Silicon Valley ecosystem that created bit-based technologies that have disrupted atom-based industries is now creating bit- and electron-based technologies that will disrupt atom-based energy industries.

Clean Disruption projections (based on technology cost curves, business model Innovationist as well as product innovation) show that by 2030:

– All new energy will be provided by solar or wind.

– All new mass-market vehicles will be electric.

– All of these vehicles will be autonomous (self-driving) or semi-autonomous.

– The car market will shrink by 80%.

– Gasoline will be obsolete. Nuclear is already obsolete. Natural Gas and Coal will be obsolete.

– Up to 80% of highways will not be needed.

– Up to 80% of parking spaces will not be needed.

– The concept of individual car ownership will be obsolete.

– The Car Insurance industry will be disrupted. The taxi industry will be obsolete.

Genesis Nanotechnology – “Great Things from Small Things”

Watch Our New YouTube Video:

Design for new electrode could boost supercapacitors’ performance – UCLA Researchers Design Super-efficient and Long-lasting electrode for Supercapacitors – 10X Efficiency


UCLA SC Boost 163903_webIMAGE: THE BRANCH-AND-LEAVES DESIGN IS MADE UP OF ARRAYS OF HOLLOW, CYLINDRICAL CARBON NANOTUBES (THE ‘BRANCHES’) AND SHARP-EDGED PETAL-LIKE STRUCTURES (THE ‘LEAVES’) MADE OF GRAPHENE. view more  CREDIT: UCLA ENGINEERING

Engineers from UCLA, 4 other universities produce nanoscale device that mimics the structure of tree branches

UCLA HENRY SAMUELI SCHOOL OF ENGINEERING OF APPLIED SCIENCE

Mechanical engineers from the UCLA Henry Samueli School of Engineering and Applied Science and four other institutions have designed a super-efficient and long-lasting electrode for supercapacitors. The device’s design was inspired by the structure and function of leaves on tree branches, and it is more than 10 times more efficient than other designs.

 

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The branch-and-leaves design is made up of arrays of hollow, cylindrical carbon nanotubes (the “branches”) and sharp-edged petal-like structures (the “leaves”) made of graphene.

The electrode design provides the same amount of energy storage, and delivers as much power, as similar electrodes, despite being much smaller and lighter. In experiments it produced 30 percent better capacitance — a device’s ability to store an electric charge — for its mass compared to the best available electrode made from similar carbon materials, and 30 times better capacitance per area. It also produced 10 times more power than other designs and retained 95 percent of its initial capacitance after more than 10,000 charging cycles.

Their work is described in the journal Nature Communications.

Supercapacitors are rechargeable energy storage devices that deliver more power for their size than similar-sized batteries. They also recharge quickly, and they last for hundreds to thousands of recharging cycles. Today, they’re used in hybrid cars’ regenerative braking systems and for other applications. Advances in supercapacitor technology could make their use widespread as a complement to, or even replacement for, the more familiar batteries consumers buy every day for household electronics.

Engineers have known that supercapacitors could be made more powerful than today’s models, but one challenge has been producing more efficient and durable electrodes. Electrodes attract ions, which store energy, to the surface of the supercapacitor, where that energy becomes available to use. Ions in supercapacitors are stored in an electrolyte solution. An electrode’s ability to deliver stored power quickly is determined in large part by how many ions it can exchange with that solution: The more ions it can exchange, the faster it can deliver power.

Knowing that, the researchers designed their electrode to maximize its surface area, creating the most possible space for it to attract electrons. They drew inspiration from the structure of trees, which are able to absorb ample amounts of carbon dioxide for photosynthesis because of the surface area of their leaves.

“We often find inspiration in nature, and plants have discovered the best way to absorb chemicals such as carbon dioxide from their environment,” said Tim Fisher, the study’s principal investigator and a UCLA professor of mechanical and aerospace engineering. “In this case, we used that idea but at a much, much smaller scale — about one-millionth the size, in fact.”

To create the branch-and-leaves design, the researchers used two nanoscale structures composed of carbon atoms. The “branches” are arrays of hollow, cylindrical carbon nanotubes, about 20 to 30 nanometers in diameter; and the “leaves” are sharp-edged petal-like structures, about 100 nanometers wide, that are made of graphene — ultra thin sheets of carbon. The leaves are then arranged on the perimeter of the nanotube stems. The leaf-like graphene petals also give the electrode stability.

The engineers then formed the structures into tunnel-shaped arrays, which the ions that transport the stored energy flow through with much less resistance between the electrolyte and the surface to deliver energy than they would if the electrode surfaces were flat.

The electrode also performs well in acidic conditions and high temperatures, both environments in which supercapacitors could be used.

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Fisher directs UCLA’s Nanoscale Transport Research Group and is a member of the California NanoSystems Institute at UCLA. Lei Chen, a professor at Mississippi State, was the project’s other principal investigator. The first authors are Guoping Xiong of the University of Nevada, Reno, and Pingge He of Central South University. The research was supported by the Air Force Office of Scientific Research.

 

Eco-Friendly Desalination using MOF’s could Supply the Lithium needed to Manufacture Batteries required to Mainstream EV’s


A new water purification (desalination) technology could be the key to more electric cars. How?

“Eco-Friendly Mining” of world’s the oceans for the vast amounts of lithium required for EV batteries, could “mainstream” our acceptance (affordability and accessibility) of Electric Vehicles and provide clean water – forecast to be in precious short supply in many parts of the World in the not so distant future.

energy_storage_2013-042216-_11-13-1Humanity is going to need a lot of lithium batteries if electric cars are going to take over, and that presents a problem when there’s only so much lithium available from conventional mines.

A potential solution is being researched that turns the world’s oceans into eco-friendly “Lithium supply mines.”

Scientists have outlined a desalination technique that would use metal-organic frameworks (sponge-like structures with very high surface areas) with sub-nanometer pores to catch lithium ions while purifying ocean water.

The approach mimics the tendency of cell membranes to selectively dehydrate and carry ions, leaving the lithium behind while producing water you can drink.

Fourth Industrial Revo 012016 AAEAAQAAAAAAAAZqAAAAJGM1YzM0NGYxLWIxZTMtNGYyNi1iMjIyLTM1MjUwNDRjYjIyYQ

While the concept of extracting lithium from our oceans certainly isn’t new, this new technology method would be much more efficient and environmentally friendly.

Instead of tearing up the landscape to find mineral deposits, battery makers would simply have to deploy enough filters.

It could even be used to make the most of water when pollution does take place — recovering lithium from the waste water at shale gas fields.

This method will require more research and development before it’s ready for real-world use.

However, the implications are already clear. If this desalination approach reaches sufficient scale, the world would have much more lithium available for electric vehicles, phones and other battery-based devices. It would also reduce the environmental impact of those devices. storedot-ev-battery-21-889x592 (1)

While some say current lithium mining practices negates some of the eco-friendliness of an EV, this “purification for Lithium” approach could let you drive relatively guilt-free

Reposted from Jonathan Fingas – Engadget

Another step closer to wearable technology with this flexible supercapacitor from NTU Singapore: YouTube Video


 

NTU Wearable download
 Scientists have created a fabric-like supercapacitor which can be cut, folded or stretched without losing its ability to store and discharge electricity. Able to retain 98% of its power capacity even after 10,000 stretch-and-release cycles, the invention brings us a step closer to powering future wearable technology. #NTUsg

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have created a customizable, fabric-like power source that can be cut, folded or stretched without losing its function.

Led by Professor Chen Xiaodong, Associate Chair (Faculty) at the School of Materials Science & Engineering, the team reported in the journal Advanced Materials (print edition 8 January) how they have created the wearable power source, a supercapacitor, which works like a fast-charging battery and can be recharged many times.

 

 

Crucially, they have made their supercapacitor customizable or “editable”, meaning its structure and shape can be changed after it is manufactured, while retaining its function as a power source. Existing stretchable supercapacitors are made into predetermined designs and structures, but the new invention can be stretched multi-directionally, and is less likely to be mismatched when it is joined up to other electrical components.

The new supercapacitor, when edited into a honeycomb-like structure, has the ability to store an electrical charge four times higher than most existing stretchable supercapacitors. In addition, when stretched to four times its original length, it maintains nearly 98 per cent of the initial ability to store electrical energy, even after 10,000 stretch-and-release cycles.

Experiments done by Prof Chen and his team also showed that when the editable supercapacitor was paired with a sensor and placed on the human elbow, it performed better than existing stretchable supercapacitors. The editable supercapacitor was able to provide a stable stream of signals even when the arm was swinging, which are then transmitted wirelessly to external devices, such as one that captures a patient’s heart rate.

The authors believe that the editable supercapacitor could be easily mass-produced as it would rely on existing manufacturing technologies. Production cost will thus be low, estimated at about SGD$0.13 (USD$0.10) to produce 1 cm2 of the material.

The team has filed a patent for the technology.

Professor Chen said, “A reliable and editable supercapacitor is important for development of the wearable electronics industry. It also opens up all sorts of possibilities in the realm of the ‘Internet-of-Things’ when wearable electronics can reliably power themselves and connect and communicate with appliances in the home and other environments.

“My own dream is to one day combine our flexible supercapacitors with wearable sensors for health and sports performance diagnostics. With the ability for wearable electronics to power themselves, you could imagine the day when we create a device that could be used to monitor a marathon runner during a race with great sensitivity, detecting signals from both under and over-exertion.”

The editable supercapacitor is made of strengthened manganese dioxide nanowire composite material. While manganese dioxide is a common material for supercapacitors, the ultralong nanowire structure, strengthened with a network of carbon nanotubes and nanocellulose fibres, allows the electrodes to withstand the associated strains during the customisation process.

The NTU team also collaborated with Dr. Loh Xian Jun, Senior Scientist and Head of the Soft Materials Department at the Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR).

Dr. Loh said, “Customisable and versatile, these interconnected, fabric-like power sources are able to offer a plug-and-play functionality while maintaining good performance. Being highly stretchable, these flexible power sources are promising next-generation ‘fabric’ energy storage devices that could be integrated into wearable electronics.”

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Watch the various customizable supercapacitors in action:

https://drive.google.com/drive/folders/16qgJpz7CKkGgVKVQeFUQxVscfZhpSAJ5

MIT: Optimizing carbon nanotube electrodes for energy storage and water desalination applications


Opt CNTs for Water Wang-Mutha-nanotubes_0Evelyn Wang (left) and Heena Mutha have developed a nondestructive method of quantifying the detailed characteristics of carbon nanotube (CNT) samples — a valuable tool for optimizing these materials for use as electrodes in a variety of practical devices. Photo: Stuart Darsch

New model measures characteristics of carbon nanotube structures for energy storage and water desalination applications.

Using electrodes made of carbon nanotubes (CNTs) can significantly improve the performance of devices ranging from capacitors and batteries to water desalination systems. But figuring out the physical characteristics of vertically aligned CNT arrays that yield the most benefit has been difficult.

Now an MIT team has developed a method that can help. By combining simple benchtop experiments with a model describing porous materials, the researchers have found they can quantify the morphology of a CNT sample, without destroying it in the process.

In a series of tests, the researchers confirmed that their adapted model can reproduce key measurements taken on CNT samples under varying conditions. They’re now using their approach to determine detailed parameters of their samples — including the spacing between the nanotubes — and to optimize the design of CNT electrodes for a device that rapidly desalinates brackish water.

A common challenge in developing energy storage devices and desalination systems is finding a way to transfer electrically charged particles onto a surface and store them there temporarily. In a capacitor, for example, ions in an electrolyte must be deposited as the device is being charged and later released when electricity is being delivered. During desalination, dissolved salt must be captured and held until the cleaned water has been withdrawn.

One way to achieve those goals is by immersing electrodes into the electrolyte or the saltwater and then imposing a voltage on the system. The electric field that’s created causes the charged particles to cling to the electrode surfaces. When the voltage is cut, the particles immediately let go.

“Whether salt or other charged particles, it’s all about adsorption and desorption,” says Heena Mutha PhD ’17, a senior member of technical staff at the Charles Stark Draper Laboratory. “So the electrodes in your device should have lots of surface area as well as open pathways that allow the electrolyte or saltwater carrying the particles to travel in and out easily.”

One way to increase the surface area is by using CNTs. In a conventional porous material, such as activated charcoal, interior pores provide extensive surface area, but they’re irregular in size and shape, so accessing them can be difficult. In contrast, a CNT “forest” is made up of aligned pillars that provide the needed surfaces and straight pathways, so the electrolyte or saltwater can easily reach them.

However, optimizing the design of CNT electrodes for use in devices has proven tricky. Experimental evidence suggests that the morphology of the material — in particular, how the CNTs are spaced out — has a direct impact on device performance. Increasing the carbon concentration when fabricating CNT electrodes produces a more tightly packed forest and more abundant surface area. But at a certain density, performance starts to decline, perhaps because the pillars are too close together for the electrolyte or saltwater to pass through easily.

Designing for device performance

OPT CNTs III graphic-1

“Much work has been devoted to determining how CNT morphology affects electrode performance in various applications,” says Evelyn Wang, the Gail E. Kendall Professor of Mechanical Engineering. “But an underlying question is, ‘How can we characterize these promising electrode materials in a quantitative way, so as to investigate the role played by such details as the nanometer-scale interspacing?'”

Inspecting a cut edge of a sample can be done using a scanning electron microscope (SEM). But quantifying features, such as spacing, is difficult, time-consuming, and not very precise. Analyzing data from gas adsorption experiments works well for some porous materials, but not for CNT forests. Moreover, such methods destroy the material being tested, so samples whose morphologies have been characterized can’t be used in tests of overall device performance.

For the past two years, Wang and Mutha have been working on a better option. “We wanted to develop a nondestructive method that combines simple electrochemical experiments with a mathematical model that would let us ‘back calculate’ the interspacing in a CNT forest,” Mutha says. “Then we could estimate the porosity of the CNT forest — without destroying it.”

Adapting the conventional model

One widely used method for studying porous electrodes is electrochemical impedance spectroscopy (EIS). It involves pulsing voltage across electrodes in an electrochemical cell at a set time interval (frequency) while monitoring “impedance,” a measure that depends on the available storage space and resistance to flow. Impedance measurements at different frequencies is called the “frequency response.”Opt CNTs II 1-newmodelmeas

The classic model describing porous media uses that frequency response to calculate how much open space there is in a porous material. “So we should be able to use [the model] to calculate the space between the carbon nanotubes in a CNT electrode,” Mutha says.

But there’s a problem: This model assumes that all pores are uniform, cylindrical voids. But that description doesn’t fit electrodes made of CNTs. Mutha modified the model to more accurately define the pores in CNT materials as the void spaces surrounding solid pillars. While others have similarly altered the classic model, Mutha took her alterations a step further. The nanotubes in a CNT material are unlikely to be packed uniformly, so she added to her equations the ability to account for variations in the spacing between the nanotubes. With this modified model, Mutha could analyze EIS data from real samples to calculate CNT spacings.

Using the model

To demonstrate her approach, Mutha first fabricated a series of laboratory samples and then measured their frequency response. In collaboration with Yuan “Jenny” Lu ’15, a materials science and engineering graduate, she deposited thin layers of aligned CNTs onto silicon wafers inside a furnace and then used water vapor to separate the CNTs from the silicon, producing free-standing forests of nanotubes. To vary the CNT spacing, she used a technique developed by MIT collaborators in the Department of Aeronautics and Astronautics, Professor Brian Wardle and postdoc associate Itai Stein PhD ’16. Using a custom plastic device, she mechanically squeezed her samples from four sides, thereby packing the nanotubes together more tightly and increasing the volume fraction — that is, the fraction of the total volume occupied by the solid CNTs.

To test the frequency response of the samples, she used a glass beaker containing three electrodes immersed in an electrolyte. One electrode is the CNT-coated sample, while the other two are used to monitor the voltage and to absorb and measure the current. Using that setup, she first measured the capacitance of each sample, meaning how much charge it could store in each square centimeter of surface area at a given constant voltage. She then ran EIS tests on the samples and analyzed results using her modified porous media model.

Results for the three volume fractions tested show the same trends. As the voltage pulses become less frequent, the curves initially rise at about a 45 degree slope. But at some point, each one shifts toward vertical, with resistance becoming constant and impedance continuing to rise.

As Mutha explains, those trends are typical of EIS analyses. “At high frequencies, the voltage changes so quickly that — because of resistance in the CNT forest — it doesn’t penetrate the depth of the entire electrode material, so the response comes only from the surface or partway in,” she says. “But eventually the frequency is low enough that there’s time between pulses for the voltage to penetrate and for the whole sample to respond.”

Resistance is no longer a noticeable factor, so the line becomes vertical, with the capacitance component causing impedance to rise as more charged particles attach to the CNTs. That switch to vertical occurs earlier with the lower-volume-fraction samples. In sparser forests, the spaces are larger, so the resistance is lower.

The most striking feature of Mutha’s results is the gradual transition from the high-frequency to the low-frequency regime. Calculations from a model based on uniform spacing — the usual assumption — show a sharp transition from partial to complete electrode response. Because Mutha’s model incorporates subtle variations in spacing, the transition is gradual rather than abrupt. Her experimental measurements and model results both exhibit that behavior, suggesting that the modified model is more accurate.

By combining their impedance spectroscopy results with their model, the MIT researchers inferred the CNT interspacing in their samples. Since the forest packing geometry is unknown, they performed the analyses based on three- and six-pillar configurations to establish upper and lower bounds. Their calculations showed that spacing can range from 100 nanometers in sparse forests to below 10 nanometers in densely packed forests.

Comparing approaches

Work in collaboration with Wardle and Stein has validated the two groups’ differing approaches to determining CNT morphology. In their studies, Wardle and Stein use an approach similar to Monte Carlo modeling, which is a statistical technique that involves simulating the behavior of an uncertain system thousands of times under varying assumptions to produce a range of plausible outcomes, some more likely than others. For this application, they assumed a random distribution of “seeds” for carbon nanotubes, simulated their growth, and then calculated characteristics, such as inter-CNT spacing with an associated variability. Along with other factors, they assigned some degree of waviness to the individual CNTs to test the impact on the calculated spacing.

To compare their approaches, the two MIT teams performed parallel analyses that determined average spacing at increasing volume fractions. The trends they exhibited matched well, with spacing decreasing as volume fraction increases. However, at a volume fraction of about 26 percent, the EIS spacing estimates suddenly go up — an outcome that Mutha believes may reflect packing irregularities caused by buckling of the CNTs as she was densifying them.

To investigate the role played by waviness, Mutha compared the variabilities in her results with those in Stein’s results from simulations assuming different degrees of waviness. At high volume fractions, the EIS variabilities were closest to those from the simulations assuming little or no waviness. But at low volume fractions, the closest match came from simulations assuming high waviness.

Based on those findings, Mutha concludes that waviness should be considered when performing EIS analyses — at least in some cases. “To accurately predict the performance of devices with sparse CNT electrodes, we may need to model the electrode as having a broad distribution of interspacings due to the waviness of the CNTs,” she says. “At higher volume fractions, waviness effects may be negligible, and the system can be modeled as simple pillars.”

The researchers’ nondestructive yet quantitative technique provides device designers with a valuable new tool for optimizing the morphology of porous electrodes for a wide range of applications. Already, Mutha and Wang have been using it to predict the performance of supercapacitors and desalination systems. Recent work has focused on designing a high-performance, portable device for the rapid desalination of brackish water. Results to date show that using their approach to optimize the design of CNT electrodes and the overall device simultaneously can as much as double the salt adsorption capacity of the system, while speeding up the rate at which clean water is produced.

This research was supported in part by the MIT Energy Initiative Seed Fund Program and by the King Fahd University of Petroleum and Minerals (KFUPM) in Dhahran, Saudi Arabia, through the Center for Clean Water and Clean Energy at MIT and KFUPM. Mutha’s work was supported by a National Science Foundation Graduate Research Fellowship and Stein’s work by the Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program.