New Carbon Material Multiplies Renewable Energy Storage

The researchers believe their use of the new material called graphene could eventually double the capacity of existing ultracapacitors, which now 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," says Rod Ruoff, a mechanical engineering professor and a physical chemist at the university.

"There are reasons to think that the ability to store electrical charge can be about double that of current commercially used materials," said Ruoff today. "We are working to see if that prediction will be borne out in the laboratory."

Two main methods exist to store electrical energy - in rechargeable batteries and in ultracapacitors, which are becoming increasingly commercialized but are not yet as widely known.

Ultracapacitors are used in energy capture and storage applications either by themselves as the primary power source or in combination with batteries or fuel cells.

Ruoff says they have higher power capability, longer life, a wider temperature operating range, lighter, more flexible packaging and lower maintenance than batteries.

Turbine at the King Mountain Wind Ranch near Odessa, Texas generates no power until the wind blows, making energy storage a critical issue. (Photo courtesy Cielo Wind Power)

With financial support from the Texas Nanotechnology Research Superiority Initiative, Ruoff and his team 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 of the graphene material has already rivaled the values available in existing ultracapacitors, and computer modeling suggests it may be possible to double that 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," says Ruoff.

Graphene's surface equals nearly the area of a football field in about 1/500th of a pound of material, says Ruoff, which 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."

Storage is crucial for times when the wind does not blow or the sun does not shine. During those times, stored electrical energy can be delivered through the electrical grid as needed.

The U.S. Department of Energy has said that an improved method for storage of electrical energy is one of the main challenges preventing the substantial installation of renewable energies such as wind and solar power.

Graduate student Meryl Stoller, a member of Ruoff's team, says the technology could greatly improve the efficiency and performance of electric and hybrid cars, buses, trains and trams, even office copiers and cell phones.

Ruoff says the growth of wind power is occurring throughout the world and in the United States, with Texas first in the generation of electricity from the wind.

According to the American Wind Energy Association, in 2007 U.S. wind power installation grew 45 percent.

Ruoff says if the energy production from wind turbine technology grew at 45 percent annually for the next 20 years, the total energy production from wind alone would almost equal the entire energy production of the world from all sources in 2007.