Activated graphene boosts supercaps
R Colin Johnson
5/18/2011 2:17 PM EDT
PORTLAND, Ore.—The U.S. Department of Energy (DoE)'s Brookhaven National Laboratory recently characterized activated graphene fabricated at the University of Texas-Austin, concluding that it had an energy density that could rival batteries, an energy-release and quick-recharge rate that exceeded batteries, and a lifetime of at least 10,000 charge/discharge cycles. Used instead of batteries, activated-graphene supercapacitors could last 27 years for a plug-in vehicle recharged once a day.
The DoE also speculates that gigantic activated-graphene supercapacitors at power-stations could smooth out power availability from intermittent energy sources, such as wind and solar.
The activated graphene material acts like a sponge for electrons because capacitors store energy on their plates, whose area has been vastly multiplied due to the nanoscale porous texture imparted by the activation process. Modeled on the activated charcoal used in high-performance filters, but adapted for atomic-scale graphene, the resulting capacitor plate surface becomes textured at the nanoscale—as if rows of nanometer-diameter nanotubes were slit down the edge and turned inside out.
The University of Texas team, led by professor Rodney Ruoff, used potassium hydroxide to activate the graphene surfaces of the supercapacitor-like plates, which were confirmed to have the negative curvature characteristic of inside-out nanotubes by researcher Eric Stach and colleague Dong Su at Brookhaven National Laboratory.
Dong Su (left) and Eric Stach study samples of activated graphene at Brookhaven’s Center for Functional Nanomaterials. Source: Brookhaven National Laboratory.
"The material’s three-dimensional nanoscale structure consists of a network of highly curved, single-atom-thick walls forming tiny pores with widths ranging from one to five nanometers," said Stach.
Stach and Su characterized the activated graphene at the Lab’s Center for Functional Nanomaterials using the National Synchrotron Light Source. The National Center for Electron Microscopy at Lawrence Berkeley National Laboratory also contributed to the characterization
Currently the researchers are working to optimize the size of the pores for capacitive storage, catalysis, and as fuel cells.
Funding for the project was provided by the DoE’s Office of Science, the Office of Science, the National Science Foundation, and the Advanced Technology Institute.
Atomic resolution electron micrograph of activated graphene in single sheets of crystalline carbon which are highly curved to form a three-dimensional porous network.