Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and the University of Texas—Austin have discovered that activated grapheme, a new form of carbon, acts like a super-absorbent sponge when it comes to soaking up electric charge. In future the material could be incorporated into “supercapacitor” energy-storage devices with very high storage capacity, approaching the energy density of lead-acid batteries, while retaining other attractive attributes such as very fast energy release, quick recharge time, and a lifetime of at least 10,000 charge/discharge cycles.
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.
The UT-Austin team set out to create a more porous form of carbon by using potassium hydroxide to restructure chemically modified graphene platelets — a form of carbon where the atoms are arrayed in tile-like rings laying flat to form single-atom-thick sheets. Such “chemical activation” has been previously used to create various forms of “activated carbon,” which have pores that increase surface area and are used in filters and other applications, including supercapacitors.
A paper co-authored by Brookhaven materials scientist Eric Stach and published in the journal Science on May 12 describes the material.
