Energy-Storing Nanomaterial Made From Hemp | Chemical & Engineering News
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Web Date: May 15, 2013

Energy-Storing Nanomaterial Made From Hemp

Electronics: Researchers turn agricultural waste into a carbon nanomaterial for high-power supercapacitors
Department: Science & Technology
News Channels: Materials SCENE, Nano SCENE
Keywords: energy storage, hemp, supercapacitor, agricultural waste, graphene, nanomaterials, Cannabis sativa
Power Plant
This hemp fiber comes from a part of the cannabis plant called the bast and can be used as a feedstock for graphenelike nanomaterials.
Credit: Zhi Li
Photograph of hemp fiber.
Power Plant
This hemp fiber comes from a part of the cannabis plant called the bast and can be used as a feedstock for graphenelike nanomaterials.
Credit: Zhi Li

Graphene might one day be used in batteries, solar cells, transparent electrodes, and a host of other electronic gadgets. But graphene is still quite expensive to make. Now researchers at the University of Alberta have demonstrated a low-cost process for turning agricultural waste into graphenelike nanomaterials for use in energy storage electronics (ACS Nano 2013, DOI: 10.1021/nn400731g).

With high surface area and conductivity, graphene is ideal for use as electrodes in batteries and supercapacitors, which are energy storage devices that excel at providing quick bursts of power. Supercapacitors charge and discharge faster than batteries can because they store energy in the form of fast-moving charges on the surfaces of their electrodes. Currently, supercapacitors are used in braking systems for buses and fast-charging flashlights.

Commercial supercapacitors use activated carbon electrodes, but experimental devices made with graphene can store more energy. Unfortunately, graphene’s production costs can’t come close to competing with the price for activated carbon, about $40 per kilogram, says University of Alberta chemical engineer David Mitlin.

Part of Mitlin’s research is finding ways to use plant waste as feedstocks for commercial materials. He thought he could transform waste from the cannabis plant (Cannabis sativa) into a carbon nanomaterial that had similar properties to graphene and with a much smaller price tag. The cannabis plant’s notorious use is for producing marijuana, but people also grow the plant to use its fibrous parts for products such as rope, clothing, oil, and plastics. The plants used for these industrial applications are referred to as hemp, and have lower levels of psychoactive compounds. Hemp is relatively inexpensive, since the plant grows rapidly in a variety of climates without the need for fertilizer and pesticides.

Mitlin and his colleagues focused on a barklike layer of the plant called the bast, which is usually incinerated or sent to landfills during industrial hemp production. “Hemp bast is a nanocomposite made up of layers of lignin, hemicellulose, and crystalline cellulose,” Mitlin says. “If you process it the right way, it separates into nanosheets similar to graphene.”

The Alberta researchers start the process by heating the bast at 180 °C for 24 hours. During this step, the lignin and hemicellulose break down, and the crystalline cellulose begins to carbonize. The researchers then treat the carbonized material with potassium hydroxide and crank up the temperature to 700 to 800 °C, causing it to exfoliate into nanosheets riddled with pores 2 to 5 nm in diameter. These thin, porous materials provide a quick path for charges to move in and out, which is important when a supercapacitor charges and discharges.

The team built a supercapacitor using the nanosheets as electrodes and an ionic liquid as an electrolyte. The best property of the device, Mitlin says, is its maximum power density, a measure of how much power a given mass of the material can produce. At 60 °C, the material puts out 49 kW/kg; activated carbon used in commercial electrodes supplies 17 kW/kg at that temperature.

Liming Dai, a chemical engineer at Case Western Reserve University, says the hempbased material shows promise as a low-cost substitute for graphene. Yury Gogotsi, a materials scientist at Drexel University, sees room for improvement. He points out that the 24-hour high-temperature process will have some associated costs when scaled up. But he’s impressed by this first step. Finding scalable production methods like this one will be key, Gogotsi says, if researchers want to move nanostructured materials out of the lab and into the marketplace.

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Malcolm J. Brenner (May 15, 2013 4:31 PM)
The cannabis plant is like donuts on "The Simpsons." Is there ANYTHING it can't do? (In addition to getting you high, of course!)
Brenda (May 17, 2013 3:28 PM)
HEMP is not marijuana--it won't get you high--it's like trying to smoke cabbage...but hemp does have plenty of great uses!
shayne (May 15, 2013 5:54 PM)
Super awesome work. Great potential for replacing platinum in fuel cells as well..
Johempes Kepler (May 15, 2013 7:28 PM)
I want my Money back! All those kilograms of hemp burnt have a value!
bobbyb (May 15, 2013 10:26 PM)
the god plant strikes again
Kenn Amdahl (May 19, 2013 3:01 PM)
Industrial hemp, while in the same family, is not marijuana. It has almost no "medicinal" qualities. But it looks so similar to regular weed (although much taller) that it was outlawed at the same time. Columbus' sails were made of material derived from hemp. When Colorado legalized weed, it also legalized hemp to be grown on experimental plots. Very useful stuff, but not for smoking.
Stephen Daniel (May 21, 2013 7:53 AM)
Actually industrial hemp has good medicine in it. Hemp can not get people high but that does not mean it is not loaded with non-psychoactive cannabinoids in the flower tops. It can be grown to have higher yields of CBD. Make no mistake about it, hemp has more CBD than most medicinal marijuana. This would make good medicine for epilepsy, cancer and a plethora of other diseases. When CBD is bred up THC is bred down and vise versa.
doublewah (July 7, 2014 2:01 PM)
It is quite possible that the prohibition of marijuana was BECAUSE of the many uses of hemp, not to mention the medicinal value of marijuana.
The oil industry, the plastics industry, the tree-to-paper industry, the prescription pills industry, and the prison industry have all benefited greatly from making marijuana (and anything that looks like it) illegal.
Wasim T Mahdi (June 16, 2013 1:14 PM)
thank you very much i m very interested to work on graphene field .Can you help me to get admission to complet ph.D study and i have scholler ship from my contary , but search on suppervisor
Lewis Goudy (January 5, 2014 8:05 PM)
" people also grow the plant to use its fibrous parts for products such as rope, clothing, oil, and plastic"

Oil is derived from the seeds rather than the fibrous parts. Wikipedia:

"About 30–35% of the weight of hempseed is an edible oil that contains about 80% as essential fatty acids (EFAs)...The proportions of linoleic acid and alpha-linolenic acid in one tablespoon per day (15 ml) of hempseed oil easily provides human daily requirements for EFAs. Unlike flaxseed oil, hempseed oil can be used continuously without developing a deficiency or other imbalance of EFAs."
TRM (February 10, 2014 11:10 PM)
If you get high off hemp you don't need drugs because you have one hell of an imagination!

49 kW/kg is a very good start.
Shane Green (March 5, 2014 11:33 PM)
The hemp's medical realm veers around a actual high or psychological relief. The medical properties I believe that are in question are its ability to kill tumor cells all the way to its ability to slowing the deterioration of ones eye sight.

I truly agree with you and chose engineering over the medical field. I consider 49 kW/kg one of the first stepping stones to a lifelong career in biodegradable renewable energy sources.
RealHemp LLC (August 12, 2014 11:40 AM)
Simply an excellent display of human ingenuity! Nice work. Looking forward to seeing this progress through the various industries.
Karl B. Hensel (August 20, 2014 1:15 AM)
What is the tensile strength in comparison to graphene? It is wonderful that you have uncovered such a usage. Might I suggest that after the 24 hour initial heating that you expose the material to dry ice. I believe you may be pleasantly surprised at the crystallization that may result. I have no formal training or even an education beyond some minor college work. I envision reactions to different exposed materials in my mind and come to conclusions based on just that. Crazy I know. I have tread also that it was attempted with some results with graphene oxide.
I have no lab equipment whatsoever. May I ask. What substrate material and how would you transfer this product? I understand that widow glass has been discussed. I hope I got that name right.
Flexible wearable are the latest trend it appears. Is this something that can be utilized? Also one last thing. Is there an image using a STEM I can use as a visual for my thoughts.

Drew (April 18, 2015 8:13 AM)
I have read that graphene has highly conductive properties and is also very strong. If this hemp process can substitute for graphene with similar properties, perhaps it can be a substitute for copper if the price can be brought in line with the cost of copper products.

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