Graphene is a super material that is 100 times stronger than steel, conducts electricity better than copper, and is more flexible than rubber. It’s used in electronics but it’s prohibitively expensive to produce – so David Mitlin of Clarkson University, New York has discovered a way to replicate at least some of its properties with cheap hemp fiber leftover from textiles and building materials. His team has managed to upcycle these fibers into supercapacitors – energy storage devices that are quickly transforming the way electronics are powered. His findings were recently published in the ACS Nano Journal and presented at the American Chemical Society meeting in San Francisco.
How on earth did Mitlin’s team turn left over bast fiber from hemp processing into an extremely valuable supercapacitor? The first step, he explains, “is to cook it – almost like a pressure cooker. It’s called hydrothermal synthesis. Once you dissolve the lignin and the semicellulose, it leaves these carbon nanosheets – a pseudo-graphene structure.” 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.
Mitlin admits that hemp fiber can’t do everything that graphene can, but for energy storage it works just as well and costs a fraction of the price. In fact, the ACS Nano journal ranks it “on par with or better than commercial graphene-based devices”. The Journal touts the hemp fiber’s properties saying that they work down to 0C and display some of the best power-energy combinations reported in the literature for any carbon. Fully assembled, their energy density is 12 Wh/kg, which can be achieved at a charge time of less than six seconds.
Mitlin has started a small company, Alta Supercaps, in hopes of beginning small-scale manufacturing. It plans to market devices to the oil and gas industries – where high-temperature operation is a valuable asset. He recently moved to the U.S. from Canada coinciding with a change in regulatory attitudes towards hemp production – signaling that hemp could be making a comeback.