May 152011
 

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have helped to uncover the nanoscale structure of a novel form of carbon, contributing to an explanation of why this new material acts like a super-absorbent sponge when it comes to soaking up electric charge.

The material, which was recently created at The University of Texas — Austin, can be incorporated into “supercapacitor” energy-storage devices with remarkably high storage capacity while retaining other attractive attributes such as superfast energy release, quick recharge time, and a lifetime of at least 10,000 charge/discharge cycles.

“Those properties make this new form of carbon particularly attractive for meeting electrical energy storage needs that also require a quick release of energy — for instance, in electric vehicles or to smooth out power availability from intermittent energy sources, such as wind and solar power,” said Brookhaven materials scientist Eric Stach, a co-author on a paper describing the material published in Science on May 12, 2011.

Supercapacitors are similar to batteries in that both store electric charge. Batteries do so through chemical reactions between metallic electrodes and a liquid electrolyte. Because these chemicals take time to react, energy is stored and released relatively slowly. But batteries can store a lot of energy and release it over a fairly long time.

Supercapacitors, on the other hand, store charge in the form of ions on the surface of the electrodes, similar to static electricity, rather than relying on chemical reactions. Charging the electrodes causes ions in the electrolyte to separate, or polarize, as well — so charge gets stored at the interface between the electrodes and the electrolyte. Pores in the electrode increase the surface area over which the electrolyte can flow and interact — increasing the amount of energy that can be stored.

But because most supercapacitors can’t hold nearly as much charge as batteries, their use has been limited to applications where smaller amounts of energy are needed quickly, or where long life cycle is essential, such as in mobile electronic devices.

The new material developed by the UT-Austin researchers may change that. Supercapacitors made from it have an energy-storage capacity, or energy density, that is approaching the energy density of lead-acid batteries, while retaining the high power density — that is, rapid energy release — that is characteristic of supercapacitors.

“This new material combines the attributes of both electrical storage systems,” said University of Texas team leader Rodney Ruoff. “We were rather stunned by its exceptional performance.”

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