Andreas Späth

Cannabis batteries for green energy storage

2014-09-15 11:38

Andreas Wilson-Späth

If you’ve watched the documentary film Bringing It Home (it won the Silver Tree Audience Choice Award at the inaugural Cape Town Eco Film Festival earlier this year), you’ll be aware of the incredible versatility of industrial hemp, which can be used to make building materials, clothing, food and more.

Now, breakthrough research has identified this amazing eco-friendly crop as a viable raw material for energy storage devices that may be used in future to efficiently bank electricity generated from renewable sources like the sun and wind. And just in case you’re wondering, we’re not talking about dagga here, but a close relative in the genus Cannabis that doesn’t contain enough of the main psychoactive ingredient of marijuana (tetrahydrocannabinol or THC) to get you high if you smoke it.

The energy storage devices in question are called supercapacitors (also known as ultracapacitors or electric double-layer capacitors). Unlike conventional electrochemical batteries, supercapacitors create an electrical field between two parallel conductor plates (electrodes) separated by a membrane that is permeable to ions and immersed in an electrolyte.

Electrically charged ions are stored on the surface of the porous electrode material, which typically consist of some or other form of carbon, such as activated carbon or carbon fibre cloth.

Compared to batteries, supercapacitors can be charged and discharged much more quickly (in minutes or seconds instead of hours) and they have a much longer operational life since they can be put through charge/discharge cycles much more frequently. They also operate across a wider range of temperatures, take up less space and are already being used in various applications from handheld electronic gadgets and solar-powered street lamps to hybrid vehicles and electric busses.

On the downside, early superconductors can only store a fraction of the electricity typically held in batteries. But this shortcoming is fast becoming a thing of the past as scientists have constructed supercapacitors with electrodes made out of graphene, a super sexy substance that consists of one-atom-thick sheets of carbon.

Graphene is eco-friendly (nothing but pure carbon), lightweight, flexible but strong, and it is an efficient conductor of both heat and electricity. The property that has made it the frontrunner in supercapacitor development is its extremely large surface area which allows for a much improved energy storage capacity.

Supercapacitors manufactured out of a combination of graphene and carbon nanotubes, for instance, have been shown to be able to trap similar amounts of electrostatic electricity as conventional lithium batteries.

Now, a group of researcher based in Canada have demonstrated that hemp-based supercapacitors may improve on grapheme ones.

Using a simple technique, they have made thin carbon nanosheets out of hemp bast fibre (derived from the inner bark or bast that surrounds the stem of the hemp plant) and used them as supercapacitor electrode material. The fibre is a waste product of industrial hemp processing and the carbon nanosheets it yields were found to have an energy storage capacity on par with that of graphene. What makes the hemp nanosheets especially attractive, however, is that they may be as much as a thousand times cheaper than graphene.

If you’re uncomfortable with the idea of using a cannabis product to store your electricity (there is really no need to be!), you’ll be excited to hear that a team of Chinese scientists have come up with a way of using the discarded shells of pistachio nuts to produce similar carbon sheets with “amazing” porosity and surface area that make for efficient supercapacitor electrodes.

I have no doubt that renewable energy sources are the future, and since storing electricity generated by solar and wind power plants when it’s not needed is one of the major challenges of the technology, it’s very exciting that we are finding ways of doing so which use waste products of natural resources that can be sustainably grown on the land.

I can’t wait for a time when I get my electricity from a renewable energy storage facility built on cannabis and pistachio nuts.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
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