Tag Archives: ASME

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.

ASME’s introductory nanotechnology podcast doesn’t mention the word billionth

It’s a landmark moment, I have never before come across an introductory nanotechnology presentation where they make no reference to ‘billionth’ as in, nanometre means one billionth of a metre.

The American Society of Mechanical Engineers now known as ASME offers a series of podcasts about nanotechnology on its website. This page is where you can sign up to get free access. (You might want to take a look at that agreement before submitting it. More about that later.) I saw the first installation on Andrew Maynard’s 2020 Science blog here. Andrew is prominently featured in this first podcast.

I enjoyed the podcast and found this new approach to introducing nanotechnology quite intriguing and I suspect they’re going in the right direction. 1 billionth of a metre or of a second doesn’t really convey that much information for most of us. Personally, I visualize the existence of alternate realities, tiny worlds of atoms and molecules which I believe to be present but are not perceptible to me through my senses.

It’s been decades since I first saw a representation of an atom or a molecule but the resemblance to planets has often played in my imagination since. They will always be planets for me, regardless of the fact that more accurate representations exist than the ones I saw so many years ago.

I think it’s the poetic aspect of it all, as if we carry worlds within us while our own planet may be simply an atom in someone else’s universe. One of these days when I have a better handle on what I’m trying to say here,  I will write a poem about it.

Actually, I’ve been meaning to do a series of poems based on the periodic table of elements ever since I saw a revisioning of the periodic table, The Chemical Galaxy by Philip Stewart. The desire was reawakened recently on finding Sam Kean’s series Blogging the Periodic Table, for Slate Magazine. From Kean’s first entry,

I’m blogging about the periodic table this month in conjunction with my new book, The Disappearing Spoon: And Other True Tales of Madness, Love, and the History of the World From the Periodic Table of the Elements. Now, I know not everyone has fond memories of the periodic table, but it got to me early—thanks to one element, mercury. I used to break those old-fashioned mercury thermometers all the time as a kid (accidentally, I swear), and I was always fascinated to see the little balls of liquid metal rolling around on the floor. My mother used to sweep them up with a toothpick, and we kept a jar with a pecan-size glob of all the mercury from all the broken thermometers on a knickknack shelf in our house.

But what really reinforced my love of mercury—and got me interested in the periodic table as a whole—was learning about all the places that mercury popped up in history. Lewis and Clark hauled 600 mercury-laced laxative tablets with them when they explored the interior of America—historians have tracked down some places where they stayed based on deposits in the soil. The so-called mad hatters (like the one in Alice in Wonderland) went crazy because of the mercury in the vats in which they cleaned fur pelts.

Mercury made me see how many different areas of life the periodic table intersects with, and I wrote The Disappearing Spoon because I realized that you can say the same about every single element on the table. There are hidden tales about familiar elements like gold, carbon, and lead and even obscure elements like tellurium and molybdenum have wonderful, often wild back stories.

There are eight more entries as of 11:25 am PST, July 15, 2010. I wish Kean good luck as he sells his book. By the way, he’ll be blogging until early August 2010.

Getting back to ASME and their nanotechnology podcasts. I haven’t signed up and am not sure I will. They are insisting on copyright in their  user agreement (link to page),

Copyrights. All rights, including copyright and database right, in this Site and its contents (including, but not limited to, all text, images, software, video clips, audio clips) (collectively, “Content”), are owned by the American Society of Mechanical Engineers (ASME), or otherwise used by ASME as permitted by applicable law or agreement.

Content Displayed on the Website. User shall not remove, obscure or alter the Content. User shall not distribute, rent, lease, transfer or otherwise make the Content available to any third party, or use the Content for systematic downloading, and/or the making of print or electronic copies for transmission to non-subscribers. User may download only the video clips designated on the Website as downloadable and may not share video URLs with non-subscribers. [emphases mine]

If I read those passages correctly, I’m prevented from copying any portion of the materials from their website and reproducing them on this blog to nonsubscribers. (I trust reproducing portions of their ‘user agreement’ won’t land me into trouble.) Since I copy and excerpt with a very high rate of frequency (being careful to give attribution and links while excerpting portions only), I don’t want to be placed in the position of having to ask for permission each and every time I’d like to copy something from the ASME site.  A lot of my entries are timely so I don’t want to wait and, frankly, I don’t understand what their problems with activities such as mine might be.  I suspect that this agreement will prove overly prohibitive and I hope the ASME folks will reconsider their approach to copyright. I really would like to view a few of their podcasts.