Supercapacitors can be built from hemp "on a par with or better than graphene" - the industry gold standard.
Alta Supercaps plans to market hemp-based supercapacitor devices to the oil and gas industries where high-temperature operation is a valuable asset.
In the process, cannabis bark is "cooked" to form graphine-like carbon nanosheets with high surface area which is very conducive to supercapacitors. By fabricating these sheets into electrodes and adding an ionic liquid as the electrolyte, it is possible to make supercapacitors which operate at a broad range of temperatures and high energy density. The hemp-based devices yielded energy densities as high as 12 Watt-hours per kilogram, two to three times higher than commercial counterparts. They also operate over an impressive temperature range, from freezing to more than 200 degrees Fahrenheit.
Dr David Mitlin of Clarkson University, New York describes his device in the journal ACS Nano:
Interconnected Carbon Nanosheets Derived from Hemp for Ultrafast Supercapacitors with High EnergyWe created unique interconnected partially graphitic carbon nanosheets (10-30 nm in thickness) with high specific surface area (up to 2287 m2 g-1), significant volume fraction of mesoporosity (up to 58%), and good electrical conductivity (211-226 S m-1) from hemp bast fiber. The nanosheets are ideally suited for low (down to 0 °C) through high (100 °C) temperature ionic-liquid-based supercapacitor applications: At 0 °C and a current density of 10 A g-1, the electrode maintains a remarkable capacitance of 106 F g-1. At 20, 60, and 100 °C and an extreme current density of 100 A g-1, there is excellent capacitance retention (72-92%) with the specific capacitances being 113, 144, and 142 F g-1, respectively. These characteristics favorably place the materials on a Ragone chart providing among the best power-energy characteristics (on an active mass normalized basis) ever reported for an electrochemical capacitor: At a very high power density of 20 kW kg-1 and 20, 60, and 100 °C, the energy densities are 19, 34, and 40 Wh kg-1, respectively. Moreover the assembled supercapacitor device yields a maximum energy density of 12 Wh kg-1, which is higher than that of commercially available supercapacitors. By taking advantage of the complex multilayered structure of a hemp bast fiber precursor, such exquisite carbons were able to be achieved by simple hydrothermal carbonization combined with activation. This novel precursor-synthesis route presents a great potential for facile large-scale production of high-performance carbons for a variety of diverse applications including energy storage.
http://pubs.acs.org/doi/abs/10.1021/nn400731g