Hemp waste being used for energy storage devices

Hemp waste being used for energy storage devices

Presenting their findings at San Francisco's American Chemical Society meeting, the researchers outlined their process of "cooking" cannabis bark into carbon nanosheets and making a supercapacitor. These energy storage devices, they claim, are of equal or better quality than graphene - the global industry standard.

This hemp technology can be harnessed for use in electric cars and power tools. "We're making graphene-like materials for a thousandth of the price - and we're doing it with waste," says Dr. David Mitlin of Clarkson University in New York. The hemp the scientists are studying has no THC in it, which makes it perfectly legal to harvest.

In countries like Canada, China and the UK, hemp is increasingly being grown in industrial quantities for use in clothing and building materials. Unfortunately, the leftover bast fibre usually ends up in landfills. "It's a waste product looking for a value-added application," Dr. Mitlin says. "People are almost paying you to take it away."

Mitlin's research team is taking these fibres and recycling them into supercapacitors, a method of energy storage that is revolutionizing the way we power electronics. While conventional batteries hold large amounts of power that slowly gets discharged, a supercapacitor can quickly unload its entire reservoir.

This makes them ideal for electric cars, and other machines that require short bursts of energy. Being able to release power in such a way requires high surface area electrodes - one of several distinct properties that make graphene a "miracle material." Graphene, a form of carbon that exists as a sheet, is composed of atoms arranged in a two-dimensional honeycomb structure.

Stronger than steel and more conductive than copper, graphene has been heralded as a possible replacement for silicon in electronics since its discovery in 2004. But despite its phenomenal qualities, graphene production is still prohibitively expensive for use in commercial supercapacitors.

That's why Dr. Mitlin first started looking for cheap and sustainable alternatives. Having experimented with all manner of biowaste - from banana peels to eggs and peat moss - he's figured out the best way to harness it. By studying a plant fibre's unique organic structure, scientists can select the appropriate electrical device to pair it with.

Banana peels, for instance, can be turned into dense blocks of carbon - called pseudo-graphite - which is great for sodium ion batteries. But hemp fibres have a much different structure; existing in high surface area sheets, they are perfect for use in supercapacitors.

The first step is called hydrothermal synthesis, which Mitlin likens to using a pressure cooker. Carbon nanosheets, which have a pseudo-graphene structure, are obtained from dissolving the lignin and semicellulose. The sheets are then fabricated into electrodes, and ionic liquid is added. The resulting supercapacitor can be used in a wide range of temperatures.

While making direct comparisons to their competition is tough, Mitlin describes his devices as "on par with or better than" existing commercial devices built on graphene. Though he concedes that hemp can't do everything that graphene can, he believes it works just as well for energy storage - and costs a fraction of the price.

Armed with his research, Miltin started a small manufacturing company called Alta Supercaps. Aiming to market his devices to the gas and oil industries, he believes that hemp has the power to transform economies.

Recommended news