Researchers at the George Washington University's Micro-propulsion and Nanotechnology Laboratory have combined two carbon nanostructures with complementary properties, mixing graphene flakes with single-walled carbon nanotubes. The resulting material shows great promise for use in fabricating electrodes for a new breed of high-performance, low-cost ultracapacitors.
According to the researchers, single-walled carbon nanotubes and graphene each have unique and excellent electronic, thermal, and mechanical properties that make them attractive materials for designing new ultracapacitors. While many research groups had explored the use of the two materials separately, few had looked at combining them.
The researchers synthesized the graphene flakes and nanotubes by using an electric arc to vaporize a hollow graphite rod filled with metallic catalyst powder. The two nanostructured materials were mixed together to form an ink, which was rolled onto paper that was then used as a separator in an ultracapacitor configuration. The result: the combination device’s specific capacitance, a measurement of the performance of a capacitor per unit of weight, was three times higher than the specific capacitance of a device made from carbon nanotubes alone.
The advantage of the hybrid structure is that the graphene flakes provide high surface area and good in-plane conductivity, while the carbon nanotubes connect all of the structures to form a uniform network, according to the researchers.
The research team has also developed a simple manufacturing process to produce large amounts of the desirable mix of carbon nanostructures at a low cost.
The research was supported by a partnership of the National Science Foundation and the U.S. Department of Energy.