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Hemp used to make graphene-like supercapacitors

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A group of scientists from the University of Alberta have created a process that makes graphene-like nanomaterials out of hemp waste, suitable for use in supercapacitors.

While graphene is already known to be a good energy store, it's also expensive, so commercial supercapacitors use activated carbon electrodes.

According to a paper published by the American Chemical Society, the material created by the University of Alberta group has a power density of up to 49 kWatt-hours per kilo (depending on temperature), capacitance up to 142 Farads per gram, and able to support current density of 100 amps per gram.

According to University of Alberta chemical engineer David Mitlin, hemp bast – a waste product in industrial hemp production – is suitable for processing into nanosheets. He told the ACS publication Chemical and Engineering News that bast is “a nanocomposite made up of layers of lignin, hemicellulose, and crystalline cellulose. If you process it the right way, it separates into nanosheets similar to graphene.”

The processing involves heating the bast to break down the lignin and hemicellulose, and to carbonise the crystalline cellulose. The resulting material is treated with potassium hydroxide, heated to between 700 and 800°C, at which point it exfoliates into sheets with pores between 2nm and 5nm in diameter. The pores provide the path for quick charging and discharging, when the hemp-waste electrodes are assembled with an ionic electrolyte.

The group says the 12 Wh per kilo density of the assembled supercapacitor is “higher than that of commercially available supercapacitors.” ®

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