Graphene resembles a single layer of carbon allotrope graphite and has unique electrical properties. Now, American and Chinese scientists have used it in the electrodes of a supercapacitor with 85.6 Watt hours per kilogram at room temperature and almost twice that value at 80 °C. This energy density is comparable to that of commonly used nickel metal hydride rechargeable batteries. There is an important difference, however, NiMH batteries can take several hours to charge whereas the graphene supercapacitor charges in minutes, giving it great potential in mobile device applications.

• Graphene-Based Supercapacitor with an Ultrahigh Energy Density
  C. Liu, Z. Yu, D. Neff, A. Zhamu, B. Z. Jang,
  Nano Lett. 2010, 10.
  DOI: 10.1021/nl102661q