September 18, 2008: Engineers and scientists at the U. of Texas/Austin have achieved a breakthrough in the use of graphene as a new carbon-based material for storing electrical charge in ultracapacitor devices, perhaps paving the way for the massive installation of renewable energies such as wind and solar power.
The researchers believe their breakthrough shows promise that the one-atom thick structure, a form of carbon, could eventually double the capacity of existing ultracapacitors, which are manufactured using an entirely different form of carbon.
“Through such a device, electrical charge can be rapidly stored on the graphene sheets, and released from them as well for the delivery of electrical current and, thus, electrical power,” according to Rod Ruoff, a mechanical engineering professor and a physical chemist. “There are reasons to think that the ability to store electrical charge can be about double that of current commercially used materials. We are working to see if that prediction will be borne out in the laboratory.”
Ruoff and his team from the Mechanical Engineering Department and the Texas Materials Institute at the university prepared chemically modified graphene material and, using several types of common electrolytes, have constructed and electrically tested graphene-based ultracapacitor cells. The amount of electrical charge stored per weight (i.e., “specific capacitance”) of the graphene material has already rivaled the values available in existing ultracapacitors, and modeling suggests the possibility of doubling the capacity.
“Our interest derives from the exceptional properties of these atom-thick and electrically conductive graphene sheets, because in principle all of the surface of this new carbon material can be in contact with the electrolyte,” according to Ruoff. “Graphene’s surface area of 2630 m2/gram — almost the area of a football field in about 1/500th of a pound of material — means that a greater number of positive or negative ions in the electrolyte can form a layer on the graphene sheets resulting in exceptional levels of stored charge.”
This technology, Stoller says, has the promise of significantly improving the efficiency and performance of electric and hybrid cars, buses, trains and trams. Even everyday devices such as office copiers and cell phones benefit from the improved power delivery and long lifetimes of ultracapacitors.
The group’s findings have been published online by the journal Nano Letters, ahead of its Oct. 8 edition.