As hemp regains prevalence in the United States thanks to loosened bans on cultivations, researchers report its fibers could be as effective as graphene, which is the "model material" for supercapacitors.
Supercapacitors are energy storage devices that could transform the way electronics are powered. Unlike modern rechargeable batteries, supercapacitors can charge and recharge within a matter of seconds. The problem is these devices cannot store as much energy (known as energy density), the American Chemical Society reported.
To boost the suercapacitor's energy density researchers have been working on designing better electrodes; researchers figured out how to create them from hemp fibers, which can hold as much energy as graphene.
"Our device's electrochemical performance is on par with or better than graphene-based devices," David Mitlin, Ph.D., said. "The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene."
Graphene is an exceptionally light material made up of one-atom-thick layers of carbon that can be made into electrodes when stacked; but hemp fibers are often discarded and could serve the same purpose. Researchers have long suspected hemp could be used as an effective electrode, but just needed to figure out how.
"We've pretty much figured out the secret sauce of it," Mitlin said. "The trick is to really understand the structure of a starter material and to tune how it's processed to give you what would rightfully be called amazing properties."
The team found if they heated the fibers for 24 hours at a temperature of a little over 350 degrees Fahrenheit and blasted the plant with more intense heat it would form into carbon nanosheets.
The research team built their supercapacitors using the "hemp-derived carbons as electrodes and an ionic liquid as the electrolyte." The devices proved to perform much better than commercial supercapacitors in both energy density and the range of temperatures at which they function. The devices yielded energy densities of 12 Watt-hours per kilogram, which is two or three times higher than most known devices.
"We're past the proof-of-principle stage for the fully functional supercapacitor," Mitlin said. "Now we're gearing up for small-scale manufacturing."
The research will be presented at the 248th National Meeting & Exposition of the American Chemical Society (ACS).
