Tag Archives: supercapacitors

Mimicking the architecture of materials like wood and bone

Caption: Microstructures like this one developed at Washington State University could be used in batteries, lightweight ultrastrong materials, catalytic converters, supercapacitors and biological scaffolds. Credit: Washington State University

A March 3, 2017 news item on Nanowerk features a new 3D manufacturing technique for creating biolike materials, (Note: A link has been removed)

Washington State University nanotechnology researchers have developed a unique, 3-D manufacturing method that for the first time rapidly creates and precisely controls a material’s architecture from the nanoscale to centimeters. The results closely mimic the intricate architecture of natural materials like wood and bone.

They report on their work in the journal Science Advances (“Three-dimensional microarchitected materials and devices using nanoparticle assembly by pointwise spatial printing”) and have filed for a patent.

A March 3, 2017 Washington State University news release by Tina Hilding (also on EurekAlert), which originated the news item, expands on the theme,

“This is a groundbreaking advance in the 3-D architecturing of materials at nano- to macroscales with applications in batteries, lightweight ultrastrong materials, catalytic converters, supercapacitors and biological scaffolds,” said Rahul Panat, associate professor in the School of Mechanical and Materials Engineering, who led the research. “This technique can fill a lot of critical gaps for the realization of these technologies.”

The WSU research team used a 3-D printing method to create foglike microdroplets that contain nanoparticles of silver and to deposit them at specific locations. As the liquid in the fog evaporated, the nanoparticles remained, creating delicate structures. The tiny structures, which look similar to Tinkertoy constructions, are porous, have an extremely large surface area and are very strong.

Silver was used because it is easy to work with. However, Panat said, the method can be extended to any other material that can be crushed into nanoparticles – and almost all materials can be.

The researchers created several intricate and beautiful structures, including microscaffolds that contain solid truss members like a bridge, spirals, electronic connections that resemble accordion bellows or doughnut-shaped pillars.

The manufacturing method itself is similar to a rare, natural process in which tiny fog droplets that contain sulfur evaporate over the hot western Africa deserts and give rise to crystalline flower-like structures called “desert roses.”

Because it uses 3-D printing technology, the new method is highly efficient, creates minimal waste and allows for fast and large-scale manufacturing.

The researchers would like to use such nanoscale and porous metal structures for a number of industrial applications; for instance, the team is developing finely detailed, porous anodes and cathodes for batteries rather than the solid structures that are now used. This advance could transform the industry by significantly increasing battery speed and capacity and allowing the use of new and higher energy materials.

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

Three-dimensional microarchitected materials and devices using nanoparticle assembly by pointwise spatial printing by Mohammad Sadeq Saleh, Chunshan Hu, and Rahul Panat. Science Advances  03 Mar 2017: Vol. 3, no. 3, e1601986 DOI: 10.1126/sciadv.1601986

This paper appears to be open access.

Finally, there is a video,

Understanding how carbon nanotubes grow and self-organize is key to better production

This research may help to commercialize use of carbon nanotubes (CNTs), a  ‘magical’ nanoscale material with great promise and great difficulties (standardizing production being one of the main difficulties). A Feb. 10, 2017 news item on phys.org describes how researchers at the Lawrence Livermore National Laboratory (LLNL) and other collaborators have recorded carbon nanotubes self-organizing,

For the first time, Lawrence Livermore National Laboratory scientists and collaborators have captured a movie of how large populations of carbon nanotubes grow and align themselves.

Understanding how carbon nanotubes (CNT) nucleate, grow and self-organize to form macroscale materials is critical for application-oriented design of next-generation supercapacitors, electronic interconnects, separation membranes and advanced yarns and fabrics.

A Feb. 9, 2017 LLNL news release, which originated the news item, provides more information about the research (Note: Links have been removed),

New research by LLNL scientist Eric Meshot and colleagues from Brookhaven National Laboratory (link is external) (BNL) and Massachusetts Institute of Technology (link is external) (MIT) has demonstrated direct visualization of collective nucleation and self-organization of aligned carbon nanotube films inside of an environmental transmission electron microscope (ETEM).

In a pair of studies reported in recent issues of Chemistry of Materials (link is external) and ACS Nano (link is external), the researchers leveraged a state-of-the-art kilohertz camera in an aberration-correction ETEM at BNL to capture the inherently rapid processes that govern the growth of these exciting nanostructures.

Among other phenomena discovered, the researchers are the first to provide direct proof of how mechanical competition among neighboring carbon nanotubes can simultaneously promote self-alignment while also frustrating and limiting growth.

“This knowledge may enable new pathways toward mitigating self-termination and promoting growth of ultra-dense and aligned carbon nanotube materials, which would directly impact several application spaces, some of which are being pursued here at the Laboratory,” Meshot said.

Meshot has led the CNT synthesis development at LLNL for several projects, including those supported by the Laboratory Directed Research and Development (LDRD) program and the Defense Threat Reduction Agency (link is external) (DTRA) that use CNTs as fluidic nanochannels for applications ranging from single-molecule detection to macroscale membranes for breathable and protective garments.

Here’s a link to and a citation for the both of the papers mentioned in the news release,

Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy by Mostafa Bedewy, B. Viswanath, Eric R. Meshot, Dmitri N. Zakharov, Eric A. Stach, and A. John Hart. Chem. Mater., 2016, 28 (11), pp 3804–3813 DOI: 10.1021/acs.chemmater.6b00798 Publication Date (Web): May 23, 2016

Copyright © 2016 American Chemical Society

Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth by Viswanath Balakrishnan, Mostafa Bedewy, Eric R. Meshot, Sebastian W. Pattinson, Erik S. Polsen, Fabrice Laye, Dmitri N. Zakharov, Eric A. Stach, and A. John Hart. ACS Nano, 2016, 10 (12), pp 11496–11504 DOI: 10.1021/acsnano.6b07251 Publication Date (Web): November 23, 2016

Copyright © 2016 American Chemical Society

Both papers are behind a paywall.

The researchers have also provided this image which allows you to appreciate the difference between a ‘scientific’ version of the work and an artistic version,

This transmission electron microscope image shows growth of a dense carbon nanotube population. Courtesy: LLNL

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.

Wearable tech for Christmas 2015 and into 2016

This is a roundup post of four items to cross my path this morning (Dec. 17, 2015), all of them concerned with wearable technology.

The first, a Dec. 16, 2015 news item on phys.org, is a fluffy little piece concerning the imminent arrival of a new generation of wearable technology,

It’s not every day that there’s a news story about socks. But in November [2015], a pair won the Best New Wearable Technology Device Award at a Silicon Valley conference. The smart socks, which track foot landings and cadence, are at the forefront of a new generation of wearable electronics, according to an article in Chemical & Engineering News (C&EN), the weekly newsmagazine of the American Chemical Society [ACS].

That news item was originated by a Dec. 16, 2015 ACS news release on EurekAlert which adds this,

Marc S. Reisch, a senior correspondent at C&EN, notes that stiff wristbands like the popular FitBit that measure heart rate and the number of steps people take have become common. But the long-touted technology needed to create more flexible monitoring devices has finally reached the market. Developers have successfully figured out how to incorporate stretchable wiring and conductive inks in clothing fabric, program them to transmit data wirelessly and withstand washing.

In addition to smart socks, fitness shirts and shoe insoles are on the market already or are nearly there. Although athletes are among the first to gain from the technology, the less fitness-oriented among us could also benefit. One fabric concept product — designed not for covering humans but a car steering-wheel — could sense driver alertness and make roads safer.

Reisch’s Dec. 7, 2015 article (C&EN vol. 93, issue 48, pp. 28-90) provides more detailed information and market information such as this,

Materials suppliers, component makers, and apparel developers gathered at a printed-electronics conference in Santa Clara, Calif., within a short drive of tech giants such as Google and Apple, to compare notes on embedding electronics into the routines of daily life. A notable theme was the effort to stealthily [emphasis mine] place sensors on exercise shirts, socks, and shoe soles so that athletes and fitness buffs can wirelessly track their workouts and doctors can monitor the health of their patients.

“Wearable technology is becoming more wearable,” said Raghu Das, chief executive officer of IDTechEx [emphasis mine], the consulting firm that organized the conference. By that he meant the trend is toward thinner and more flexible devices that include not just wrist-worn fitness bands but also textiles printed with stretchable wiring and electronic sensors, thanks to advances in conductive inks.

Interesting use of the word ‘stealthy’, which often suggests something sneaky as opposed to merely secretive. I imagine what’s being suggested is that the technology will not impose itself on the user (i.e., you won’t have to learn how to use it as you did with phones and computers).

Leading into my second item, IDC (International Data Corporation), not to be confused with IDTechEx, is mentioned in a Dec. 17, 2015 news item about wearable technology markets on phys.org,

The global market for wearable technology is seeing a surge, led by watches, smart clothing and other connected gadgets, a research report said Thursday [Dec. 16, 2015].

IDC said its forecast showed the worldwide wearable device market will reach a total of 111.1 million units in 2016, up 44.4 percent from this year.

By 2019, IDC sees some 214.6 million units, or a growth rate averaging 28 percent.

A Dec. 17, 2015 IDC press release, which originated the news item, provides more details about the market forecast,

“The most common type of wearables today are fairly basic, like fitness trackers, but over the next few years we expect a proliferation of form factors and device types,” said Jitesh Ubrani , Senior Research Analyst for IDC Mobile Device Trackers. “Smarter clothing, eyewear, and even hearables (ear-worn devices) are all in their early stages of mass adoption. Though at present these may not be significantly smarter than their analog counterparts, the next generation of wearables are on track to offer vastly improved experiences and perhaps even augment human abilities.”

One of the most popular types of wearables will be smartwatches, reaching a total of 34.3 million units shipped in 2016, up from the 21.3 million units expected to ship in 2015. By 2019, the final year of the forecast, total shipments will reach 88.3 million units, resulting in a five-year CAGR of 42.8%.

“In a short amount of time, smartwatches have evolved from being extensions of the smartphone to wearable computers capable of communications, notifications, applications, and numerous other functionalities,” noted Ramon Llamas , Research Manager for IDC’s Wearables team. “The smartwatch we have today will look nothing like the smartwatch we will see in the future. Cellular connectivity, health sensors, not to mention the explosive third-party application market all stand to change the game and will raise both the appeal and value of the market going forward.

“Smartwatch platforms will lead the evolution,” added Llamas. “As the brains of the smartwatch, platforms manage all the tasks and processes, not the least of which are interacting with the user, running all of the applications, and connecting with the smartphone. Once that third element is replaced with cellular connectivity, the first two elements will take on greater roles to make sense of all the data and connections.”

Top Five Smartwatch Platform Highlights

Apple’s watchOS will lead the smartwatch market throughout our forecast, with a loyal fanbase of Apple product owners and a rapidly growing application selection, including both native apps and Watch-designed apps. Very quickly, watchOS has become the measuring stick against which other smartwatches and platforms are compared. While there is much room for improvement and additional features, there is enough momentum to keep it ahead of the rest of the market.

Android/Android Wear will be a distant second behind watchOS even as its vendor list grows to include technology companies (ASUS, Huawei, LG, Motorola, and Sony) and traditional watchmakers (Fossil and Tag Heuer). The user experience on Android Wear devices has been largely the same from one device to the next, leaving little room for OEMs to develop further and users left to select solely on price and smartwatch design.

Smartwatch pioneer Pebble will cede market share to AndroidWear and watchOS but will not disappear altogether. Its simple user interface and devices make for an easy-to-understand use case, and its price point relative to other platforms makes Pebble one of the most affordable smartwatches on the market.

Samsung’s Tizen stands to be the dark horse of the smartwatch market and poses a threat to Android Wear, including compatibility with most flagship Android smartphones and an application selection rivaling Android Wear. Moreover, with Samsung, Tizen has benefited from technology developments including a QWERTY keyboard on a smartwatch screen, cellular connectivity, and new user interfaces. It’s a combination that helps Tizen stand out, but not enough to keep up with AndroidWear and watchOS.

There will be a small, but nonetheless significant market for smart wristwear running on a Real-Time Operating System (RTOS), which is capable of running third-party applications, but not on any of these listed platforms. These tend to be proprietary operating systems and OEMs will use them when they want to champion their own devices. These will help within specific markets or devices, but will not overtake the majority of the market.

The company has provided a table with five-year CAGR (compound annual growth rate) growth estimates, which can be found with the Dec. 17, 2015 IDC press release.

Disclaimer: I am not endorsing IDC’s claims regarding the market for wearable technology.

For the third and fourth items, it’s back to the science. A Dec. 17, 2015 news item on Nanowerk, describes, in general terms, some recent wearable technology research at the University of Manchester (UK), Note: A link has been removed),

Cheap, flexible, wireless graphene communication devices such as mobile phones and healthcare monitors can be directly printed into clothing and even skin, University of Manchester academics have demonstrated.

In a breakthrough paper in Scientific Reports (“Highly Flexible and Conductive Printed Graphene for Wireless Wearable Communications Applications”), the researchers show how graphene could be crucial to wearable electronic applications because it is highly-conductive and ultra-flexible.

The research could pave the way for smart, battery-free healthcare and fitness monitoring, phones, internet-ready devices and chargers to be incorporated into clothing and ‘smart skin’ applications – printed graphene sensors integrated with other 2D materials stuck onto a patient’s skin to monitor temperature, strain and moisture levels.

Detail is provided in a Dec. 17, 2015 University of Manchester press release, which originated the news item, (Note: Links have been removed),

Examples of communication devices include:

• In a hospital, a patient wears a printed graphene RFID tag on his or her arm. The tag, integrated with other 2D materials, can sense the patient’s body temperature and heartbeat and sends them back to the reader. The medical staff can monitor the patient’s conditions wirelessly, greatly simplifying the patient’s care.

• In a care home, battery-free printed graphene sensors can be printed on elderly peoples’ clothes. These sensors could detect and collect elderly people’s health conditions and send them back to the monitoring access points when they are interrogated, enabling remote healthcare and improving quality of life.

Existing materials used in wearable devices are either too expensive, such as silver nanoparticles, or not adequately conductive to have an effect, such as conductive polymers.

Graphene, the world’s thinnest, strongest and most conductive material, is perfect for the wearables market because of its broad range of superlative qualities. Graphene conductive ink can be cheaply mass produced and printed onto various materials, including clothing and paper.

“Sir Kostya Novoselov

To see evidence that cheap, scalable wearable communication devices are on the horizon is excellent news for graphene commercial applications.

Sir Kostya Novoselov (tweet)„

The researchers, led by Dr Zhirun Hu, printed graphene to construct transmission lines and antennas and experimented with these in communication devices, such as mobile and Wifi connectivity.

Using a mannequin, they attached graphene-enabled antennas on each arm. The devices were able to ‘talk’ to each other, effectively creating an on-body communications system.

The results proved that graphene enabled components have the required quality and functionality for wireless wearable devices.

Dr Hu, from the School of Electrical and Electronic Engineering, said: “This is a significant step forward – we can expect to see a truly all graphene enabled wireless wearable communications system in the near future.

“The potential applications for this research are huge – whether it be for health monitoring, mobile communications or applications attached to skin for monitoring or messaging.

“This work demonstrates that this revolutionary scientific material is bringing a real change into our daily lives.”

Co-author Sir Kostya Novoselov, who with his colleague Sir Andre Geim first isolated graphene at the University in 2004, added: “Research into graphene has thrown up significant potential applications, but to see evidence that cheap, scalable wearable communication devices are on the horizon is excellent news for graphene commercial applications.”

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

Highly Flexible and Conductive Printed Graphene for Wireless Wearable Communications Applications by Xianjun Huang, Ting Leng, Mengjian Zhu, Xiao Zhang, JiaCing Chen, KuoHsin Chang, Mohammed Aqeeli, Andre K. Geim, Kostya S. Novoselov, & Zhirun Hu. Scientific Reports 5, Article number: 18298 (2015) doi:10.1038/srep18298 Published online: 17 December 2015

This is an open access paper.

The next and final item concerns supercapacitors for wearable tech, which makes it slightly different from the other items and is why, despite the date, this is the final item. The research comes from Case Western Research University (CWRU; US) according to a Dec. 16, 2015 news item on Nanowerk (Note: A link has been removed),

Wearable power sources for wearable electronics are limited by the size of garments.

With that in mind, researchers at Case Western Reserve University have developed flexible wire-shaped microsupercapacitors that can be woven into a jacket, shirt or dress (Energy Storage Materials, “Flexible and wearable wire-shaped microsupercapacitors based on highly aligned titania and carbon nanotubes”).

A Dec. 16, 2015 CWRU news release (on EurekAlert), which originated the news item, provides more detail about a device that would make wearable tech more wearable (after all, you don’t want to recharge your clothes the same way you do your phone and other mobile devices),

By their design or by connecting the capacitors in series or parallel, the devices can be tailored to match the charge storage and delivery needs of electronics donned.

While there’s been progress in development of those electronics–body cameras, smart glasses, sensors that monitor health, activity trackers and more–one challenge remaining is providing less obtrusive and cumbersome power sources.

“The area of clothing is fixed, so to generate the power density needed in a small area, we grew radially-aligned titanium oxide nanotubes on a titanium wire used as the main electrode,” said Liming Dai, the Kent Hale Smith Professor of Macromolecular Science and Engineering. “By increasing the surface area of the electrode, you increase the capacitance.”

Dai and Tao Chen, a postdoctoral fellow in molecular science and engineering at Case Western Reserve, published their research on the microsupercapacitor in the journal Energy Storage Materials this week. The study builds on earlier carbon-based supercapacitors.

A capacitor is cousin to the battery, but offers the advantage of charging and releasing energy much faster.

How it works

In this new supercapacitor, the modified titanium wire is coated with a solid electrolyte made of polyvinyl alcohol and phosphoric acid. The wire is then wrapped with either yarn or a sheet made of aligned carbon nanotubes, which serves as the second electrode. The titanium oxide nanotubes, which are semiconducting, separate the two active portions of the electrodes, preventing a short circuit.

In testing, capacitance–the capability to store charge–increased from 0.57 to 0.9 to 1.04 milliFarads per micrometer as the strands of carbon nanotube yarn were increased from 1 to 2 to 3.

When wrapped with a sheet of carbon nanotubes, which increases the effective area of electrode, the microsupercapactitor stored 1.84 milliFarads per micrometer. Energy density was 0.16 x 10-3 milliwatt-hours per cubic centimeter and power density .01 milliwatt per cubic centimeter.

Whether wrapped with yarn or a sheet, the microsupercapacitor retained at least 80 percent of its capacitance after 1,000 charge-discharge cycles. To match various specific power needs of wearable devices, the wire-shaped capacitors can be connected in series or parallel to raise voltage or current, the researchers say.

When bent up to 180 degrees hundreds of times, the capacitors showed no loss of performance. Those wrapped in sheets showed more mechanical strength.

“They’re very flexible, so they can be integrated into fabric or textile materials,” Dai said. “They can be a wearable, flexible power source for wearable electronics and also for self-powered biosensors or other biomedical devices, particularly for applications inside the body.” [emphasis mine]

Dai ‘s lab is in the process of weaving the wire-like capacitors into fabric and integrating them with a wearable device.

So one day we may be carrying supercapacitors in our bodies? I’m not sure how I feel about that goal. In any event, here’s a link and a citation for the paper,

Flexible and wearable wire-shaped microsupercapacitors based on highly aligned titania and carbon nanotubes by Tao Chen, Liming Dai. Energy Storage Materials Volume 2, January 2016, Pages 21–26 doi:10.1016/j.ensm.2015.11.004

This paper appears to be open access.

Shape memory in a supercapacitor fibre for ‘smart’ textiles (wearable tech: 1 of 3)

Wearable technology seems to be quite trendy for a grouping not usually seen: consumers, fashion designers, medical personnel, manufacturers, and scientists.

The first in this informal series concerns a fibre with memory shape. From a Nov. 19, 2015 news item on Nanowerk (Note: A link has been removed),

Wearing your mobile phone display on your jacket sleeve or an EKG probe in your sports kit are not off in some distant imagined future. Wearable “electronic textiles” are on the way. In the journal Angewandte Chemie (“A Shape-Memory Supercapacitor Fiber”), Chinese researchers have now introduced a new type of fiber-shaped supercapacitor for energy-storage textiles. Thanks to their shape memory, these textiles could potentially adapt to different body types: shapes formed by stretching and bending remain “frozen”, but can be returned to their original form or reshaped as desired.

A Nov. 19, 2015 Wiley Publishers press release, which originated the news item, provides context and detail about the work,

Any electronic components designed to be integrated into textiles must be stretchable and bendable. This is also true of the supercapacitors that are frequently used for data preservation in static storage systems (SRAM). SRAM is a type of storage that holds a small amount of data that is rapidly retrievable. It is often used for caches in processors or local storage on chips in devices whose data must be stored for long periods without a constant power supply. Some time ago, a team headed by Huisheng Peng at Fudan University developed stretchable, pliable fiber-shaped supercapacitors for integration into electronic textiles. Peng and his co-workers have now made further progress: supercapacitor fibers with shape memory.

Any electronic components designed to be integrated into textiles must be stretchable and bendable. This is also true of the supercapacitors that are frequently used for data preservation in static storage systems (SRAM). SRAM is a type of storage that holds a small amount of data that is rapidly retrievable. It is often used for caches in processors or local storage on chips in devices whose data must be stored for long periods without a constant power supply.
Some time ago, a team headed by Huisheng Peng at Fudan University developed stretchable, pliable fiber-shaped supercapacitors for integration into electronic textiles. Peng and his co-workers have now made further progress: supercapacitor fibers with shape memory.

The fibers are made using a core of polyurethane fiber with shape memory. This fiber is wrapped with a thin layer of parallel carbon nanotubes like a sheet of paper. This is followed by a coating of electrolyte gel, a second sheet of carbon nanotubes, and a final layer of electrolyte gel. The two layers of carbon nanotubes act as electrodes for the supercapacitor. Above a certain temperature, the fibers produced in this process can be bent as desired and stretched to twice their original length. The new shape can be “frozen” by cooling. Reheating allows the fibers to return to their original shape and size, after which they can be reshaped again. The electrochemical performance is fully maintained through all shape changes.

Weaving the fibers into tissues results in “smart” textiles that could be tailored to fit the bodies of different people. This could be used to make precisely fitted but reusable electronic monitoring systems for patients in hospitals, for example. The perfect fit should render them both more comfortable and more reliable.

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

A Shape-Memory Supercapacitor Fiber by Jue Deng, Ye Zhang, Yang Zhao, Peining Chen, Dr. Xunliang Cheng, & Prof. Dr. Huisheng Peng. Angewandte Chemie International Edition  DOI: 10.1002/anie.201508293  First published: 3 November 2015

This paper is behind a paywall.

Cellulose nanocrystals and supercapacitors at McMaster University (Canada)

Photos: Xuan Yang and Kevin Yager.

Photos: Xuan Yang and Kevin Yager. Courtesy McMaster University

I love that featherlike structure holding up a tiny block of something while balanced on what appears to be a series of medallions. What it has to do with supercapacitors (energy storage) and cellulose nanocrystals is a mystery but that’s one of the images you’ll find illustrating an Oct. 7, 2015 news item on Nanotechnology Now featuring research at McMaster University,

McMaster Engineering researchers Emily Cranston and Igor Zhitomirsky are turning trees into energy storage devices capable of powering everything from a smart watch to a hybrid car.

The scientists are using cellulose, an organic compound found in plants, bacteria, algae and trees, to build more efficient and longer-lasting energy storage devices or supercapacitors. This development paves the way toward the production of lightweight, flexible, and high-power electronics, such as wearable devices, portable power supplies and hybrid and electric vehicles.

A Sept. 10, 2015 McMaster University news release, which originated the news item, describes the research in more detail,

Cellulose offers the advantages of high strength and flexibility for many advanced applications; of particular interest are nanocellulose-based materials. The work by Cranston, an assistant chemical engineering professor, and Zhitomirsky, a materials science and engineering professor, demonstrates an improved three-dimensional energy storage device constructed by trapping functional nanoparticles within the walls of a nanocellulose foam.

The foam is made in a simplified and fast one-step process. The type of nanocellulose used is called cellulose nanocrystals and looks like uncooked long-grain rice but with nanometer-dimensions. In these new devices, the ‘rice grains’ have been glued together at random points forming a mesh-like structure with lots of open space, hence the extremely lightweight nature of the material. This can be used to produce more sustainable capacitor devices with higher power density and faster charging abilities compared to rechargeable batteries.

Lightweight and high-power density capacitors are of particular interest for the development of hybrid and electric vehicles. The fast-charging devices allow for significant energy saving, because they can accumulate energy during braking and release it during acceleration.

For anyone interested in a more detailed description of supercapacitors, there’s my favourite one which involves Captain America’s shield along with some serious science in my April 28, 2014 posting.

Getting back to the research at McMaster, here’s a link to and a citation for the paper,

Cellulose Nanocrystal Aerogels as Universal 3D Lightweight Substrates for Supercapacitor Materials by Xuan Yang, Kaiyuan Shi, Igor Zhitomirsky, and Emily D. Cranston. Advanced Materials DOI: 10.1002/adma.201502284View/save citation First published online 2 September 2015

This paper is behind a paywall.

One final bit, cellulose nanocrystals (CNC) are sometimes referred to as nanocrystalline cellulose (NCC).

Wearable technologies, electric vehicles and conundrums at Wollongong University (Australia)

A July 25, 2015 news item on Nanowerk announces research at the University of Wollongong designed to address a conundrum (Note: A link has been removed),

UOW’s Institute for Superconducting and Electronic Materials (ISEM) has successfully pioneered a way to construct a flexible, foldable and lightweight energy storage device that provides the building blocks for next-generation batteries needed to power wearable electronics and implantable medical devices (ACS Central Science, “Self-Assembled Multifunctional Hybrids: Toward Developing High-Performance Graphene-Based Architectures for Energy Storage Devices”).

The conundrum researchers have faced in developing miniature energy storage devices, such as batteries and supercapacitors, has been figuring out how to increase the surface area of the device, to store more charge, without making it larger.

A July 27, 2015 University of Wollongong news release by Grant Reynolds, which originated the news item, describes the research in more detail,

To solve this problem, a team of PhD students, led by Dr Konstantin Konstantinov under the patronage of ISEM Director Professor Shi Xue Dou and with the support of Professor Hua Kun Liu, the head of ISEM Energy Storage Division, have developed a three-dimensional structure using a flat-pack self-assembly of three components: graphene, a conductive polymer and carbon nanotubes, which are atom-thick lattice-like networks of carbon formed into cylinders.

Graphene, made from single atom-thick layers of graphite, was a suitable candidate due its electronic performance and mechanical strength.

“We knew in theory that if you can make a sort of carbon skeleton you have a greater surface area and greater surface area means more charge,” Dr Konstantinov said. “If we could efficiently separate the layers of carbon we could then use both surfaces of each layer for charge accumulation. The problem we faced was that fabricating these 3D shapes in practice, not just theory, is a challenging, if not impossible task.”

The solution was to flat-pack the components by building the 3D shape layer-by-layer, much like a miniature exercise in cake decoration. The graphene in liquid form was mixed with the conductive polymer and reduced to solid and the carbon nanotubes carefully inserted between the graphene layers to form a self-assembled flat-packed, wafer-thin supercapacitor material.

“The real challenge was how to assemble these three components into a single structure with the best use of the space available,” PhD student Monirul Islam said. “Getting the proportions or ratios of the components appropriately in order to obtain a composite material with maximum energy storage performance was another challenge.”

Wrong proportions of either ingredient result in a lumpy mess, or a 3D shape that isn’t strong enough to retain the needed flexibility as well as the charge storage ability. There’s also elegance in the simplicity of the team’s design: the researchers dispersed the components in liquid crystalline, which enabled natural chemical interactions to prevent the graphene layers clumping together.

The result was a 3D shape with, thanks to the carbon nanotubes, a massive surface area, excellent charge capacity that is also foldable. It can also be cheaply and easily fabricated without the need for expensive vacuum chambers or sophisticated equipment.

“Our graphene-based flexible composite is highly conductive, lightweight, is able to fold like a roll or stack like a paper in electronic devices to store a huge amount of charge,” Monirul said. “This material can store charge in a second and deliver the charge in superfast speed and will be more lightweight than traditional batteries used in present day’s electronics.”

The ISEM study has been financially supported by the Automotive Australia 2020 CRC as part of its research into electric vehicles. ISEM is the program leader for electrification and plays crucial role for design of next generation electric vehicles A key to unlocking the electric vehicle’s capability is a lightweight and powerful battery pack.

“Our simple fabrication method of eco-friendly materials with increased performance has great potential to be scaled up for use supercapacitor and battery technology. Our next step is to use this material to fabricate flexible wearable supercapacitors with high power density and energy density as well as large scale supercapacitors for electric vehicles.”

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

Self-Assembled Multifunctional Hybrids: Toward Developing High-Performance Graphene-Based Architectures for Energy Storage Devices by Md. Monirul Islam, Seyed Hamed Aboutalebi, Dean Cardillo, Hua Kun Liu, Konstantin Konstantinov, and Shi Xue Dou. ACS Cent. Sci., 2015, 1 (4), pp 206–216 DOI: 10.1021/acscentsci.5b00189 Publication Date (Web): July 2, 2015

Copyright © 2015 American Chemical Society

This appears to be an open access paper.

Yarns of niobium nanowire for small electronic device boost at the University of British Columbia (Canada) and Massachusetts Institute of Technology (US)

It turns out that this research concerning supercapacitors is a collaboration between the University of British Columbia (Canada) and the Massachusetts Institute of Technology (MIT). From a July 7, 2015 news item by Stuart Milne for Azonano,

A team of researchers from MIT and University of British Columbia has discovered an innovative method to deliver short bursts of high power required by wearable electronic devices.

Such devices are used for monitoring health and fitness and as such are rapidly growing in the consumer electronics industry. However, a major drawback of these devices is that they are integrated with small batteries, which fail to deliver sufficient amount of power required for data transmission.

According to the research team, one way to resolve this issue is to develop supercapacitors, which are capable of storing and releasing short bursts of electrical power required to transmit data from smartphones, computers, heart-rate monitors, and other wearable devices. supercapacitors can also prove useful for other applications where short bursts of high power is required, for instance autonomous microrobots.

A July 7, 2015 MIT news release provides more detail about the research,

The new approach uses yarns, made from nanowires of the element niobium, as the electrodes in tiny supercapacitors (which are essentially pairs of electrically conducting fibers with an insulator between). The concept is described in a paper in the journal ACS Applied Materials and Interfaces by MIT professor of mechanical engineering Ian W. Hunter, doctoral student Seyed M. Mirvakili, and three others at the University of British Columbia.

Nanotechnology researchers have been working to increase the performance of supercapacitors for the past decade. Among nanomaterials, carbon-based nanoparticles — such as carbon nanotubes and graphene — have shown promising results, but they suffer from relatively low electrical conductivity, Mirvakili says.

In this new work, he and his colleagues have shown that desirable characteristics for such devices, such as high power density, are not unique to carbon-based nanoparticles, and that niobium nanowire yarn is a promising an alternative.

“Imagine you’ve got some kind of wearable health-monitoring system,” Hunter says, “and it needs to broadcast data, for example using Wi-Fi, over a long distance.” At the moment, the coin-sized batteries used in many small electronic devices have very limited ability to deliver a lot of power at once, which is what such data transmissions need.

“Long-distance Wi-Fi requires a fair amount of power,” says Hunter, the George N. Hatsopoulos Professor in Thermodynamics in MIT’s Department of Mechanical Engineering, “but it may not be needed for very long.” Small batteries are generally poorly suited for such power needs, he adds.

“We know it’s a problem experienced by a number of companies in the health-monitoring or exercise-monitoring space. So an alternative is to go to a combination of a battery and a capacitor,” Hunter says: the battery for long-term, low-power functions, and the capacitor for short bursts of high power. Such a combination should be able to either increase the range of the device, or — perhaps more important in the marketplace — to significantly reduce size requirements.

The new nanowire-based supercapacitor exceeds the performance of existing batteries, while occupying a very small volume. “If you’ve got an Apple Watch and I shave 30 percent off the mass, you may not even notice,” Hunter says. “But if you reduce the volume by 30 percent, that would be a big deal,” he says: Consumers are very sensitive to the size of wearable devices.

The innovation is especially significant for small devices, Hunter says, because other energy-storage technologies — such as fuel cells, batteries, and flywheels — tend to be less efficient, or simply too complex to be practical when reduced to very small sizes. “We are in a sweet spot,” he says, with a technology that can deliver big bursts of power from a very small device.

Ideally, Hunter says, it would be desirable to have a high volumetric power density (the amount of power stored in a given volume) and high volumetric energy density (the amount of energy in a given volume). “Nobody’s figured out how to do that,” he says. However, with the new device, “We have fairly high volumetric power density, medium energy density, and a low cost,” a combination that could be well suited for many applications.

Niobium is a fairly abundant and widely used material, Mirvakili says, so the whole system should be inexpensive and easy to produce. “The fabrication cost is cheap,” he says. Other groups have made similar supercapacitors using carbon nanotubes or other materials, but the niobium yarns are stronger and 100 times more conductive. Overall, niobium-based supercapacitors can store up to five times as much power in a given volume as carbon nanotube versions.

Niobium also has a very high melting point — nearly 2,500 degrees Celsius — so devices made from these nanowires could potentially be suitable for use in high-temperature applications.

In addition, the material is highly flexible and could be woven into fabrics, enabling wearable forms; individual niobium nanowires are just 140 nanometers in diameter — 140 billionths of a meter across, or about one-thousandth the width of a human hair.

So far, the material has been produced only in lab-scale devices. The next step, already under way, is to figure out how to design a practical, easily manufactured version, the researchers say.

“The work is very significant in the development of smart fabrics and future wearable technologies,” says Geoff Spinks, a professor of engineering at the University of Wollongong, in Australia, who was not associated with this research. This paper, he adds, “convincingly demonstrates the impressive performance of niobium-based fiber supercapacitors.”

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

High-Performance Supercapacitors from Niobium Nanowire Yarns by Seyed M. Mirvakili, Mehr Negar Mirvakili, Peter Englezos, John D. W. Madden, and Ian W. Hunter. ACS Appl. Mater. Interfaces, 2015, 7 (25), pp 13882–13888 DOI: 10.1021/acsami.5b02327 Publication Date (Web): June 12, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Combining the best qualities of batteries and supercapacitors at the University of California at Los Angeles (UCLA)

There’s a reason why I’ve been feeling impatient about batteries and supercapacitors according to an April 2, 2015 news item on Nanowerk,

The dramatic rise of smartphones, tablets, laptops and other personal and portable electronics has brought battery technology to the forefront of electronics research. Even as devices have improved by leaps and bounds, the slow pace of battery development has held back technological progress.

Now, researchers at UCLA’s California NanoSystems Institute have successfully combined two nanomaterials to create a new energy storage medium that combines the best qualities of batteries and supercapacitors.

An April 1, 2015 UCLA news release, which originated the news item, describes the challenge and how the scientists addressed it (Note: A link has been removed),

Supercapacitors are electrochemical components that can charge in seconds rather than hours and can be used for 1 million recharge cycles. Unlike batteries, however, they do not store enough power to run our computers and smartphones.

The new hybrid supercapacitor stores large amounts of energy, recharges quickly and can last for more than 10,000 recharge cycles. The CNSI scientists also created a microsupercapacitor that is small enough to fit in wearable or implantable devices. Just one-fifth the thickness of a sheet of paper, it is capable of holding more than twice as much charge as a typical thin-film lithium battery.

The study, led by Richard Kaner, distinguished professor of chemistry and biochemistry and materials science and engineering, and Maher El-Kady, a postdoctoral scholar, was published in the Proceedings of the National Academy of Sciences.

“The microsupercapacitor is a new evolving configuration, a very small rechargeable power source with a much higher capacity than previous lithium thin-film microbatteries,” El-Kady said.

The new components combine laser-scribed graphene, or LSG — a material that can hold an electrical charge, is very conductive, and charges and recharges very quickly — with manganese dioxide, which is currently used in alkaline batteries because it holds a lot of charge and is cheap and plentiful. They can be fabricated without the need for extreme temperatures or the expensive “dry rooms” required to produce today’s supercapacitors.

“Let’s say you wanted to put a small amount of electrical current into an adhesive bandage for drug release or healing assistance technology,” Kaner said. “The microsupercapacitor is so thin you could put it inside the bandage to supply the current. You could also recharge it quickly and use it for a very long time.”

The researchers found that the supercapacitor could quickly store electrical charge generated by a solar cell during the day, hold the charge until evening and then power an LED overnight, showing promise for off-grid street lighting.

“The LSG–manganese-dioxide capacitors can store as much electrical charge as a lead acid battery, yet can be recharged in seconds, and they store about six times the capacity of state-of-the-art commercially available supercapacitors,” Kaner said. “This scalable approach for fabricating compact, reliable, energy-dense supercapacitors shows a great deal of promise in real-world applications, and we’re very excited about the possibilities for greatly improving personal electronics technology in the near future.”

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

Engineering three-dimensional hybrid supercapacitors and microsupercapacitors for high-performance integrated energy storage by Maher F. El-Kady, Melanie Ihns, Mengping Li, Jee Youn Hwang, Mir F. Mousavi, Lindsay Chaney, Andrew T. Lech, and Richard B. Kaner. Published online before print March 23, 2015, doi: 10.1073/pnas.1420398112 PNAS March 23, 2015

This paper is behind a paywall.

One last bit, Dexter Johnson in an April 3, 2015 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) provides some insight into the research,

The story of graphene in supercapacitors can be represented by the old adage: its greatest strength is its greatest weakness. Of course, the name of the game in supercapacitor energy density is surface area. The greater the surface area, the greater number of ions you can store on the electrodes. While graphene has a theoretical surface area of 2630 square meters per gram, this density is only possible with a single, standalone graphene sheet.

But you can’t actually use a standalone sheet for the electrode of a supercapacitor because it will result in a very low volumetric capacitance. ….

So, while the 2-D characteristic of graphene may limit its usable surface area for supercapacitors, it does offer a way to make supercapacitors with small dimensions, something that would be impossible with activated carbon.

It is this strength that the CNSI researchers are aiming to exploit in their supercapacitor, which is small enough to be used as a wearable or implantable device. …

I recommend reading Dexter’s post in its entirety.

Supercapacitors* on automobiles

Queensland University of Technology* (QUT; Australia) researchers are hopeful they can adapt supercapacitors in the form of a fine film tor use in electric vehicles making them more energy-efficient. From a Nov. 6, 2014 news item on ScienceDaily,

A car powered by its own body panels could soon be driving on our roads after a breakthrough in nanotechnology research by a QUT team.

Researchers have developed lightweight “supercapacitors” that can be combined with regular batteries to dramatically boost the power of an electric car.

The discovery was made by Postdoctoral Research Fellow Dr Jinzhang Liu, Professor Nunzio Motta and PhD researcher Marco Notarianni, from QUT’s Science and Engineering Faculty — Institute for Future Environments, and PhD researcher Francesca Mirri and Professor Matteo Pasquali, from Rice University in Houston, in the United States.

A Nov. 6, 2014 QUT news release, which originated the news item, describes supercapacitors, the research, and the need for this research in more detail,

The supercapacitors – a “sandwich” of electrolyte between two all-carbon electrodes – were made into a thin and extremely strong film with a high power density.

The film could be embedded in a car’s body panels, roof, doors, bonnet and floor – storing enough energy to turbocharge an electric car’s battery in just a few minutes.

“Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but they are able to deliver it very quickly, making them the perfect complement to mass-storage batteries,” he said.

“Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery.”

Dr Liu said currently the “energy density” of a supercapacitor is lower than a standard lithium ion (Li-Ion) battery, but its “high power density”, or ability to release power in a short time, is “far beyond” a conventional battery.

“Supercapacitors are presently combined with standard Li-Ion batteries to power electric cars, with a substantial weight reduction and increase in performance,” he said.

“In the future, it is hoped the supercapacitor will be developed to store more energy than a Li-Ion battery while retaining the ability to release its energy up to 10 times faster – meaning the car could be entirely powered by the supercapacitors in its body panels.

“After one full charge this car should be able to run up to 500km – similar to a petrol-powered car and more than double the current limit of an electric car.”

Dr Liu said the technology would also potentially be used for rapid charges of other battery-powered devices.

“For example, by putting the film on the back of a smart phone to charge it extremely quickly,” he said.

The discovery may be a game-changer for the automotive industry, with significant impacts on financial, as well as environmental, factors.

“We are using cheap carbon materials to make supercapacitors and the price of industry scale production will be low,” Professor Motta said.

“The price of Li-Ion batteries cannot decrease a lot because the price of Lithium remains high. This technique does not rely on metals and other toxic materials either, so it is environmentally friendly if it needs to be disposed of.”

A Nov. 10, 2014 news item on Azonano describes the Rice University (Texas, US) contribution to this work,

Rice University scientist Matteo Pasquali and his team contributed to two new papers that suggest the nano-infused body of a car may someday power the car itself.

Rice supplied high-performance carbon nanotube films and input on the device design to scientists at the Queensland University of Technology in Australia for the creation of lightweight films containing supercapacitors that charge quickly and store energy. The inventors hope to use the films as part of composite car doors, fenders, roofs and other body panels to significantly boost the power of electric vehicles.

A Nov. 7, 2014 Rice University news release, which originated the news item, offers a few technical details about the film being proposed for use as a supercapacitor on car panels,

Researchers in the Queensland lab of scientist Nunzio Motta combined exfoliated graphene and entangled multiwalled carbon nanotubes combined with plastic, paper and a gelled electrolyte to produce the flexible, solid-state supercapacitors.

“Nunzio’s team is making important advances in the energy-storage area, and we were glad to see that our carbon nanotube film technology was able to provide breakthrough current collection capability to further improve their devices,” said Pasquali, a Rice professor of chemical and biomolecular engineering and chemistry. “This nice collaboration is definitely bottom-up, as one of Nunzio’s Ph.D. students, Marco Notarianni, spent a year in our lab during his Master of Science research period a few years ago.”

“We built on our earlier work on CNT films published in ACS Nano, where we developed a solution-based technique to produce carbon nanotube films for transparent electrodes in displays,” said Francesca Mirri, a graduate student in Pasquali’s research group and co-author of the papers. “Now we see that carbon nanotube films produced by the solution-processing method can be applied in several areas.”

As currently designed, the supercapacitors can be charged through regenerative braking and are intended to work alongside the lithium-ion batteries in electric vehicles, said co-author Notarianni, a Queensland graduate student.

“Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but with their high power density, deliver it very quickly, making them the perfect complement to mass-storage batteries,” he said.

Because hundreds of film supercapacitors are used in the panel, the electric energy required to power the car’s battery can be stored in the car body. “Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared with several hours for a standard electric car battery,” Notarianni said.

The researchers foresee such panels will eventually replace standard lithium-ion batteries. “In the future, it is hoped the supercapacitor will be developed to store more energy than an ionic battery while retaining the ability to release its energy up to 10 times faster – meaning the car would be powered by the supercapacitors in its body panels,” said Queensland postdoctoral researcher Jinzhang Liu.

Here’s an image of graphene infused with carbon nantoubes used in the supercapacitor film,

A scanning electron microscope image shows freestanding graphene film with carbon nanotubes attached. The material is part of a project to create lightweight films containing super capacitors that charge quickly and store energy. Courtesy of Nunzio Motta/Queensland University of Technology - See more at: http://news.rice.edu/2014/11/07/supercharged-panels-may-power-cars/#sthash.0RPsIbMY.dpuf

A scanning electron microscope image shows freestanding graphene film with carbon nanotubes attached. The material is part of a project to create lightweight films containing super capacitors that charge quickly and store energy. Courtesy of Nunzio Motta/Queensland University of Technology

Here are links to and citations for the two papers published by the researchers,

Graphene-based supercapacitor with carbon nanotube film as highly efficient current collector by Marco Notarianni, Jinzhang Liu, Francesca Mirri, Matteo Pasquali, and Nunzio Motta. Nanotechnology Volume 25 Number 43 doi:10.1088/0957-4484/25/43/435405

High performance all-carbon thin film supercapacitors by Jinzhang Liu, Francesca Mirri, Marco Notarianni, Matteo Pasquali, and Nunzio Motta. Journal of Power Sources Volume 274, 15 January 2015, Pages 823–830 DOI: 10.1016/j.jpowsour.2014.10.104

Both articles are behind paywalls.

One final note, Dexter Johnson provides some insight into issues with graphene-based supercapacitors and what makes this proposed application attractive in his Nov. 7, 2014 post on the Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website; Note: Links have been removed),

The hope has been that someone could make graphene electrodes for supercapacitors that would boost their energy density into the range of chemical-based batteries. The supercapacitors currently on the market have on average an energy density around 28 Wh/kg, whereas a Li-ion battery holds about 200Wh/kg. That’s a big gap to fill.

The research in the field thus far has indicated that graphene’s achievable surface area in real devices—the factor that determines how many ions a supercapacitor electrode can store, and therefore its energy density—is not any better than traditional activated carbon. In fact, it may not be much better than a used cigarette butt.

Though graphene may not help increase supercapacitors’ energy density, its usefulness in this application may lie in the fact that its natural high conductivity will allow superconductors to operate at higher frequencies than those that are currently on the market. Another likely benefit that graphene will yield comes from the fact that it can be structured and scaled down, unlike other supercapacitor materials.

I recommend reading Dexter’s commentary in its entirety.

*’University of Queensland’ corrected to “Queensland University of Technology’ on Nov. 10, 2014 at 1335 PST.

* ‘super-capacitor’ changed to ‘supercapacitor’ on April 29, 2015.