Science & Environment

Hemp fibres 'better than graphene'

hemp field Image copyright Thinkstock




They presented their work at the American Chemical Society meeting in San Francisco.

"People ask me: why hemp? I say, why not?" said Dr David Mitlin of Clarkson University, New York, who describes his device in the journal ACS Nano.



Secret sauce



Image copyright SPL




Releasing this torrent requires electrodes with high surface area - one of graphene's many phenomenal properties.

Stronger than diamond, more conductive than copper and more flexible than rubber, the "miracle material" was the target of a £50m investment by UK Chancellor George Osborne.

But while this carbon monolayer is the state-of-the-art material for commercial supercapacitors, it is prohibitively expensive to produce.

Finding cheap, sustainable alternatives is the speciality of Dr Mitlin's former research group at the University of Alberta.

They have experimented with all flavours of biowaste - from peat moss to eggs. Most recently, they turned banana peel into batteries.

Image copyright Oli Scarff / Getty
Image caption George Osborne invested £50m in graphene







By fabricating these sheets into electrodes and adding an ionic liquid as the electrolyte, his team made supercapacitors which operate at a broad range of temperatures and a high energy density.

Direct comparisons with rival devices are complicated by the variety of measures for performance.

But Mitlin's peer-reviewed journal paper ranks the device "on par with or better than commercial graphene-based devices".



Image copyright SPL


Growth industry

"Obviously hemp can't do all the things graphene can," Dr Mitlin concedes.

"But for energy storage, it works just as well. And it costs a fraction of the price -$500-1,000 a tonne."

Having established a proof of principle, his start-up company Alta Supercaps is hoping to begin small-scale manufacturing.

It plans to market devices to the oil and gas industries - where high-temperature operation is a valuable asset.

His move to the US coincides with a change in regulatory attitudes - with signs that hemp could be making a comeback.

In China the crop is widely cultivated, and in Canada, the industry for textiles is growing.

"Fifty miles down the road from my house in Alberta there was an agricultural hemp processing facility. And all that bast fibre - it just sits in a high bay, and they don't know what to do with it," Dr Mitlin told BBC News.





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