Tag Archives: supercapacitors

Hemp as a substitute for graphene in supercapacitors

As a member of the Cannabis plant family, hemp has an undeserved reputation due to its cousin’s (marijuana) notoriety and consciousness-altering properties. Hemp is, by contrast, the Puritan in the family, associated by the knowledgeable with virtues of thrift and hard work.

An Aug. 12, 2014 news item on Nanowerk highlights a hemp/supercapacitor presentation at the 248th meeting of the American Chemical Society (ACS),

As hemp makes a comeback in the U.S. after a decades-long ban on its cultivation, scientists are reporting that fibers from the plant can pack as much energy and power as graphene, long-touted as the model material for supercapacitors. They’re presenting their research, which a Canadian start-up company is working on scaling up, at the 248th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society.

David Mitlin, Ph.D., explains that supercapacitors are energy storage devices that have huge potential to transform the way future electronics are powered. Unlike today’s rechargeable batteries, which sip up energy over several hours, supercapacitors can charge and discharge within seconds. But they normally can’t store nearly as much energy as batteries, an important property known as energy density. One approach researchers are taking to boost supercapacitors’ energy density is to design better electrodes. Mitlin’s team has figured out how to make them from certain hemp fibers — and they can hold as much energy as the current top contender: graphene.

An Aug. 12, 2014 ACS news release features David Mitlin, formerly of the University of Alberta (Canada) where this research took place,, Mitlin is now with now with Clarkson University in New York,

“Our device’s electrochemical performance is on par with or better than graphene-based devices,” Mitlin says. “The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene.”

The race toward the ideal supercapacitor has largely focused on graphene — a strong, light material made of atom-thick layers of carbon, which when stacked, can be made into electrodes. Scientists are investigating how they can take advantage of graphene’s unique properties to build better solar cells, water filtration systems, touch-screen technology, as well as batteries and supercapacitors. The problem is it’s expensive.

Mitlin’s group decided to see if they could make graphene-like carbons from hemp bast fibers. The fibers come from the inner bark of the plant and often are discarded from Canada’s fast-growing industries that use hemp for clothing, construction materials and other products. …

His team found that if they heated the fibers for 24 hours at a little over 350 degrees Fahrenheit, and then blasted the resulting material with more intense heat, it would exfoliate into carbon nanosheets.

Mitlin’s team built their supercapacitors using the hemp-derived carbons as electrodes and an ionic liquid as the electrolyte. Fully assembled, the devices performed far better than commercial supercapacitors in both energy density and the range of temperatures over which they can work. The hemp-based devices yielded energy densities as high as 12 Watt-hours per kilogram, two to three times higher than commercial counterparts. They also operate over an impressive temperature range, from freezing to more than 200 degrees Fahrenheit.

“We’re past the proof-of-principle stage for the fully functional supercapacitor,” he says. “Now we’re gearing up for small-scale manufacturing.”

I have not been able to confirm the name for Mitlin’s startup but I think it’s called Alta Supercaps (Alta being an abbreviation for Alberta,, amongst other things, and supercaps for supercapacitors) as per the information about a new startup on the Mitlin Group webspace (scroll down to the July 2, 2013 news item) which can still be found on the University of Alberta website (as of Aug. 12, 2014).

For those who would like more technical details, there is this July 2013 article by Mark Crawford for the ASME (American Society of Mechanical Engineers); Note: A link has been removed.

Activated carbons, templated carbons, carbon nanofibers, carbon nanotubes, and graphene have all been intensively studied as materials for supercapacitor electrodes. High manufacturing costs is one issue—another is that the power characteristics of many of these carbons are limited. This is a result of high microporosity, which increases ion transport limitations.

“It is becoming well understood that the key to achieving high power in porous electrodes is to reduce the ion transport limitations” says Mitlin. “Nanomaterials based on graphene and their hybrids have emerged as a new class of promising high-rate electrode candidates—they are, however, too expensive to manufacture compared to activated carbons derived from pyrolysis of agricultural wastes, or from the coking operations.”

Biomass, which mainly contains cellulose and lignin by-products, is widely utilized as a feedstock for producing activated carbons. Mitlin decided to test hemp bast fiber’s unique cellular structure to see if it could produce graphene-like carbon nanosheets.

Hemp fiber waste was pressure-cooked (hydrothermal synthesis) at 180 °C for 24 hours. The resulting carbonized material was treated with potassium hydroxide and then heated to temperatures as high as 800 °C, resulting in the formation of uniquely structured nanosheets. Testing of this material revealed that it discharged 49 kW of power per kg of material—nearly triple what standard commercial electrodes supply, 17 kW/kg.

Mitlin and his team successfully synthesized two-dimensional, yet interconnected, carbon nanosheets with superior electrochemical storage properties comparable to those of state-of-the-art graphene-based electrodes. “We were able to achieve this by employing a biomass precursor with a unique structure—hemp bast fiber,” says Mitlin. “The resultant graphene-like nanosheets possess fundamentally different properties—such as pore size distribution, physical interconnectedness, and electrical conductivity—as compared to conventional biomass-derived activated carbons.”

This image from Wikimedia was used to illustrate the Crawford article,

Hemp bast fiber is a low-cost graphene-like nanomaterial. Image: Wikimedia Commons

Hemp bast fiber is a low-cost graphene-like nanomaterial. Image: Wikimedia Commons

It seems to me that over the last few months there have been more than the usual number of supercapacitor stories, which makes the race to create the one that will break through in the marketplace fascinating to observe.

Don’t throw that cigarette butt away—use it to store energy!

I’ve read the news release and briefly skimmed the research paper and cannot find any discussion of how these scientists got the idea to ‘recycle’ used cigarette butts for energy storage (supercapacitors) although the inspiration seems to have its roots in a desire to create better supercapacitors from recycled materials. From an Aug. 5, 2014 news item on ScienceDaily,

A group of scientists from South Korea have converted used-cigarette butts into a high-performing material that could be integrated into computers, handheld devices, electrical vehicles and wind turbines to store energy.

Presenting their findings today, 5 August 2014, in IOP Publishing’s journal Nanotechnology, the researchers have demonstrated the material’s superior performance compared to commercially available carbon, graphene and carbon nanotubes.

It is hoped the material can be used to coat the electrodes of supercapacitors — electrochemical components that can store extremely large amounts of electrical energy — whilst also offering a solution to the growing environmental problem caused by used-cigarette filters.

An Aug. 5, 2014 Institute of Physics (IOP) news release (also on EurekAlert), which originated the news item, further describes the situation regarding used cigarette butts and the characteristics that could render them into supercapacitors

It is estimated that as many as 5.6 trillion cigarette butts (equivalent to 766 571 metric tons), are deposited into the environment worldwide every year.

Co-author of the study Professor Jongheop Yi, from Seoul National University, said: “Our study has shown that used cigarette filters can be transformed into a high-performing carbon-based material using a simple one-step process, which simultaneously offers a green solution to meeting the energy demands of society.

“Numerous countries are developing strict regulations to avoid the trillions of toxic and non-biodegradable used cigarette filters that are disposed of into the environment each year; our method is just one way of achieving this.”

Carbon is the most popular material that supercapacitors are composed of, due to its low cost, high surface area, high electrical conductivity and long-term stability.

Scientists around the world are currently working towards improving the characteristics of supercapacitors – such as energy density, power density and cycle stability – while also trying to reduce production costs.

In their study, the researchers demonstrated that the cellulose acetate fibres that cigarette filters are mostly composed of could be transformed into a carbon-based material using a simple, one-step burning technique called pyrolysis.

As a result of this burning process, the resulting carbon-based material contained a number of tiny pores, increasing its performance as a supercapacitive material.

“A high-performing supercapacitor material should have a large surface area, which can be achieved by incorporating a large number of small pores into the material,” continued Professor Yi.

“A combination of different pore sizes ensures that the material has high power densities, which is an essential property in a supercapacitor for the fast charging and discharging.”

Once fabricated, the carbon-based material was attached to an electrode and tested in a three-electrode system to see how well the material could adsorb electrolyte ions (charge) and then release them (discharge).

The material stored a higher amount of electrical energy than commercially available carbon and also had a higher amount of storage compared to graphene and carbon nanotubes, as reported in previous studies.

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

Preparation of energy storage material derived from a used cigarette filter for a supercapacitor electrode by Minzae Lee, Gil-Pyo Kim, Hyeon Don Song, Soomin Park, and Jongheop Yi. Nanotechnology 25 (34) 5601 doi:10.1088/0957-4484/25/34/345601

This is an open access paper.

Is there a supercapacitor hiding in your tree?

I gather the answer is: Yes, there is a supercapacitor in your tree as researchers at Oregon State University (OSU) have found a way to use tree cellulose as a building component for supercapacitors. From an April 7, 2014 news item on ScienceDaily,

Based on a fundamental chemical discovery by scientists at Oregon State University, it appears that trees may soon play a major role in making high-tech energy storage devices.

OSU chemists have found that cellulose — the most abundant organic polymer on Earth and a key component of trees — can be heated in a furnace in the presence of ammonia, and turned into the building blocks for supercapacitors.

An April 7, 2014 OSU news release (also on EurekAlert), which originated the news item portrays great excitement (Note: Links have been removed),

These supercapacitors are extraordinary, high-power energy devices with a wide range of industrial applications, in everything from electronics to automobiles and aviation. But widespread use of them has been held back primarily by cost and the difficulty of producing high-quality carbon electrodes.

The new approach just discovered at Oregon State can produce nitrogen-doped, nanoporous carbon membranes – the electrodes of a supercapacitor – at low cost, quickly, in an environmentally benign process. The only byproduct is methane, which could be used immediately as a fuel or for other purposes.

“The ease, speed and potential of this process is really exciting,” said Xiulei (David) Ji, an assistant professor of chemistry in the OSU College of Science, and lead author on a study announcing the discovery in Nano Letters, a journal of the American Chemical Society. The research was funded by OSU.

“For the first time we’ve proven that you can react cellulose with ammonia and create these N-doped nanoporous carbon membranes,” Ji said. “It’s surprising that such a basic reaction was not reported before. Not only are there industrial applications, but this opens a whole new scientific area, studying reducing gas agents for carbon activation.

“We’re going to take cheap wood and turn it into a valuable high-tech product,” he said.

The news release includes some technical information about the carbon membranes and information about the uses to which supercapacitors are put,

These carbon membranes at the nano-scale are extraordinarily thin – a single gram of them can have a surface area of nearly 2,000 square meters. That’s part of what makes them useful in supercapacitors. And the new process used to do this is a single-step reaction that’s fast and inexpensive. It starts with something about as simple as a cellulose filter paper – conceptually similar to the disposable paper filter in a coffee maker.

The exposure to high heat and ammonia converts the cellulose to a nanoporous carbon material needed for supercapacitors, and should enable them to be produced, in mass, more cheaply than before.

A supercapacitor is a type of energy storage device, but it can be recharged much faster than a battery and has a great deal more power. They are mostly used in any type of device where rapid power storage and short, but powerful energy release is needed.

Supercapacitors can be used in computers and consumer electronics, such as the flash in a digital camera. They have applications in heavy industry, and are able to power anything from a crane to a forklift. A supercapacitor can capture energy that might otherwise be wasted, such as in braking operations. And their energy storage abilities may help “smooth out” the power flow from alternative energy systems, such as wind energy.

They can power a defibrillator, open the emergency slides on an aircraft and greatly improve the efficiency of hybrid electric automobiles.

Besides supercapacitors, nanoporous carbon materials also have applications in adsorbing gas pollutants, environmental filters, water treatment and other uses.

“There are many applications of supercapacitors around the world, but right now the field is constrained by cost,” Ji said. “If we use this very fast, simple process to make these devices much less expensive, there could be huge benefits.”

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

Pyrolysis of Cellulose under Ammonia Leads to Nitrogen-Doped Nanoporous Carbon Generated through Methane Formation by Wei Luo, Bao Wang, Christopher G. Heron, Marshall J. Allen, Jeff Morre, Claudia S. Maier, William F. Stickle, and Xiulei Ji. Nano Lett., Article ASAP DOI: 10.1021/nl500859p Publication Date (Web): March 28, 2014
Copyright © 2014 American Chemical Society

The article is behind a paywall.

One final observation, one of the researchers, William F. Stickle is affiliated with HewLett Packard and not Oregon State University as are the others.

Stretchable carbon nanotubes as supercapacitors

This Nov. 25, 2013 news item on phys.org was a bit of a walk down memory lane for me,

A mobile telephone display for your jacket sleeve, ECG probes for your workout clothes—wearable electronics are in demand. In order for textiles with built-in electronics to function over longer periods of time, all of the components need to be flexible and stretchable. In the journal Angewandte Chemie, Chinese researchers have now introduced a new type of supercapacitor that fulfills this requirement. Its components are fiber-shaped and based on carbon nanotubes.

The reference to a mobile telephone display on a jacket sleeve brought back memories of Nokia’s proposed Morph device,, from my Aug. 3, 2011 posting,

For anyone who’s not familiar with the Morph, it’s an idea that Nokia and the University of Cambridge’s Nanoscience Centre have been working on for the last few years. Originally announced as a type of flexible phone that you could wrap around your wrist, the Morph is now called a concept.  …

At the time I was writing about exploring the use of graphene to enable the morph (flexible phone). This latest work from China is focused on carbon nanotubes,. The Angewandte Chemie Nov. 25, 2013 press release, which originated the news item on phys.org,  provides more details,

For electronic devices to be incorporated into textiles or plastic films, their components must be stretchable. This is true for LEDS, solar cells, transistors, circuits, and batteries—as well as for the supercapacitors often used for static random access memory (SRAM). SRAM is often used as a cache in processors or for local storage on chips, as well as in devices that must maintain their data over several years with no source of power.

Previous stretchable electronic components have generally been produced in a conventional planar format, which has been an obstacle to their further development for use in small, lightweight, wearable electronics. Initial attempts to produce supercapacitors in the form of wires or fibers produced flexible—but not stretchable—components. However, stretchability is a required feature for a number of applications. For example, electronic textiles would easily tear if they were not stretchable.

A team led by Huisheng Peng at Fudan University has now developed a new family of highly stretchable, fiber-shaped, high-performance supercapacitors. The devices are made by a winding process with an elastic fiber at the core. The fiber is coated with an electrolyte gel and a thin layer of carbon nanotubes is wound around it like a sheet of paper. This is followed by a second layer of electrolyte gel, another layer of carbon nanotube wrap, and a final layer of electrolyte gel.

The delicate “sheets” of carbon nanotubes are produced by chemical vapor deposition and a spinning process. In the sheets this method produces, the tiny tubes are aligned in parallel. These types of layers display a remarkable combination of properties: They are highly flexible, tear-resistant, conductive, and thermally and mechanically stable. In the wound fibers, the two layers of carbon nanotubes act as electrodes. The electrolyte gel separates the electrodes from each other while stabilizing the nanotubes during stretching so that their alignment is maintained. This results in supercapacitor fibers with a high capacity that is maintained after many stretching cycles.

For the curious, here’s a link to and a citation for the paper,

A Highly Stretchable, Fiber-Shaped Supercapacitor by Zhibin Yang, Jue Deng, Xuli Chen, Jing Ren, and Prof. Huisheng Peng. Angewandte Chemie International Edition
Early View (Online Version of Record published before inclusion in an issue)Article first published online: 8 NOV 2013 DOI: 10.1002/anie.201307619

Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Unique ‘printing’ process boosts supercapacitor performance

In addition to creating energy, we also need to store some of it for future use as a July 29, 2013 news release from the University of Central Florida notes,

Researchers at the University of Central Florida have developed a technique to increase the energy storage capabilities of supercapacitors, essential devices for powering high-speed trains, electric cars, and the emergency doors of the Airbus A380.

The finding, which offers a solution to a problem that has plagued the growing multi-billion dollar industry, utilizes a unique three-step process to “print” large – area nanostructured electrodes, structures necessary to improve electrical conductivity and boost performance of the supercapacitor.

Jayan Thomas, an assistant professor in UCF’s NanoScience Technology Center, led the project which is featured in the June edition of Advanced Materials, one of the leading peer-reviewed scientific journals covering materials science in the world. Thomas’ research appears on the journal’s highly-coveted frontispiece, the illustration page of the journal that precedes the title page.

The news release goes on to describe the supercapacitor issue the researchers were addressing,

Supercapacitors have been around since the 1960’s. Similar to batteries, they store energy. The difference is that supercapacitors can provide higher amounts of power for shorter periods of time, making them very useful for heavy machinery and other applications that require large amounts of energy to start.  However, due to their innate low energy density; supercapacitors are limited in the amount of energy that they can store.

“We had been looking at techniques to print nanostructures,” said Thomas. “Using a simple spin-on nanoprinting (SNAP) technique, we can print highly-ordered nanopillars without the need for complicated development processes. By eliminating these processes, it allows multiple imprints to be made on the same substrate in close proximity.“

This simplified fabrication method devised by Thomas and his team is very attractive for the next-generation of energy storage systems. “What we’ve found is by adding the printed ordered nanostructures to supercapacitor electrodes, we can increase their surface area many times,” added Thomas. “We discovered that supercapacitors made using the SNAP technique can store much more energy than ones made without.”

Here’s a link to and a citation for the research paper abut this new technique for supercapacitors,

Energy Storage: Highly Ordered MnO2 Nanopillars for Enhanced Supercapacitor Performance (Adv. Mater. 24/2013) by Zenan Yu, Binh Duong, Danielle Abbitt, and Jayan Thomas. Article first published online: 20 JUN 2013 DOI: 10.1002/adma.201370160 Advanced Materials Volume 25, Issue 24, page 3301, June 25, 2013.

Lead researcher Thomas was recently featured in a video for his work on creating plasmonic nanocrystals from gold nanoparticles (from the news release),

Thomas, who is also affiliated with the College of Optics and Photonics (CREOL), and the College of Engineering, was recently featured on American Institute of Physics’ Inside Science TV for his collaborative research to develop a new material using nanotechnology that could potentially help keep pilots safe by diffusing harmful laser light.

Here’s the video,

You can find videos, news, and blogs featuring other research at Inside Science and you can find out more about Dr. Jayan Thomas here.

James’ bond (Rice University research team creates graphene/nanotube hybrid)

I have to give credit to Mike Williams’ Nov. 27, 2012 Rice University news release for the “James’ bond” phrase used to describe this graphene/nanotube hybrid,

A seamless graphene/nanotube hybrid created at Rice University may be the best electrode interface material possible for many energy storage and electronics applications.

Led by Rice chemist James Tour, researchers have successfully grown forests of carbon nanotubes that rise quickly from sheets of graphene to astounding lengths of up to 120 microns, according to a paper published today by Nature Communications. A house on an average plot with the same aspect ratio would rise into space.

Seven-atom rings (in red) at the transition from graphene to nanotube make this new hybrid material a seamless conductor. The hybrid may be the best electrode interface material possible for many energy storage and electronics applications. Image courtesy of the Tour Group

The Rice hybrid combines two-dimensional graphene, which is a sheet of carbon one atom thick, and nanotubes into a seamless three-dimensional structure. The bonds between them are covalent, which means adjacent carbon atoms share electrons in a highly stable configuration. The nanotubes aren’t merely sitting on the graphene sheet; they become a part of it.

“Many people have tried to attach nanotubes to a metal electrode and it’s never gone very well because they get a little electronic barrier right at the interface,” Tour said. “By growing graphene on metal (in this case copper) and then growing nanotubes from the graphene, the electrical contact between the nanotubes and the metal electrode is ohmic. That means electrons see no difference, because it’s all one seamless material.

In the new work, the team grew a specialized odako that retained the iron catalyst and aluminum oxide buffer but put them on top of a layer of graphene grown separately on a copper substrate. The copper stayed to serve as an excellent current collector for the three-dimensional hybrids that were grown within minutes to controllable lengths of up to 120 microns.

Electron microscope images showed the one-, two- and three-walled nanotubes firmly embedded in the graphene, and electrical testing showed no resistance to the flow of current at the junction.

“The performance we see in this study is as good as the best carbon-based supercapacitors that have ever been made,” Tour said. “We’re not really a supercapacitor lab, and still we were able to match the performance because of the quality of the electrode. It’s really remarkable, and it all harkens back to that unique interface.”

Here’s the citation and a link for the article,

A seamless three-dimensional carbon nanotube graphene hybrid material by Yu Zhu, Lei Li, Chenguang Zhang, Gilberto Casillas,  Zhengzong Sun, Zheng Yan, Gedeng Ruan, Zhiwei Peng, Abdul-Rahman O. Raji, Carter Kittrell, Robert H. Hauge & James M. Tour in Nature Communications 3, Article number:1225 doi:10.1038/ncomms2234 Published 27 November 2012

This article is behind a paywall.

Walking on eggshells at the University of Alberta

It’s Friday, April 13, 2012 and I wanted a little fun in my headline so Zhi Li and his colleagues in the Mitlin Group at the University of Alberta are not walking on eggshells. They are, instead, carbonizing them as a means of increasing the amount of electrical energy that can be stored as Michael Berger explains in his April 12, 2012 article, Converting eggshell membranes into a high-performance electrode material for supercapacitors (links have been removed from the following excerpt),

Today’s commercial supercapacitors – which are mostly electric double layer capacitors (EDLC) – store energy in two closely spaced layers with opposing charges and offer fast charge/discharge rates and the ability to sustain millions of cycles. Researchers have come up with various electrode materials to improve the performance of supercapacitors, focussing mostly on porous carbon due to its high surface areas, tunable structures, good conductivities, and low cost. In recent years, this has increasingly included research on various carbon nanomaterials such as carbon nanotubes, carbon nano-onions, or graphene.

“An ideal supercapacitor is one with both high energy density and high power density,” Zhi Li, a post doc researcher in David Mitlin’s group at the University of Alberta, explains to Nanowerk. …

In new work recently published in Advanced Energy Materials (“Carbonized Chicken Eggshell Membranes with 3D Architectures as High-Performance Electrode Materials for Supercapacitors”), first-authored by Li, researchers have demonstrated that a common daily waste – the eggshell membrane – can be converted into a high-performance carbon material for supercapacitors.

“Considering over 1000 billion eggs are consumed per year globally, and that 30–40 mg finished carbon is derivable from one egg, the eggshell membrane is indeed a reliable and sustainable resource for clean energy storage,” says Li.

“The most exciting finding, for me, is that the amazing nature-made architecture of chicken eggshell membrane is critical to its performance as electrode materials after carbonization,” notes Li. “Why? The carbonized eggshell membrane is a real ‘integrated system’ composed of interwoven carbon fibers with diameter from 50 nm to 2 µm where the big fibers and tiny fibers are naturally connected together.”

As a consequence of their architecture,

… carbonized eggshell membrane can work at high current loading. That means capacitors based on it can be charged and discharged faster than capacitor based on traditional carbons.

You can find out more about the Mitlin Group here and you can find the article, “Carbonized Chicken Eggshell Membranes with 3D Architectures as High-Performance Electrode Materials for Supercapacitors,” here but it is behind a paywall. By the way, Dr. David Mitlin, group leader, is also a principal investigator at Canada’s National Institute of Technology.