There has recently been a growing demand for energy storage systems with high power for use in such diverse applications as hybrid electric vehicles, personal electronics, and industrial power backup. 1À6 Recent attention has focused on supercapacitors (also known as ultracapacitors or electrochemical capacitors) to address these demands. 2,6À14 Supercapacitors are a promising new energy storage system on account of the high chargeÀ discharge rates, simple mechanism, long cycle-life, and high power density that they possess. 5,6,13À17 Focus has presently turned to the creation of flexible supercapacitors for use in various personal soft portable electronics such as cell phones and mp3 players, where flexibility is becoming an increasingly desirable quality. 18,19 Figure 1 shows a schematic representation of a flexible supercapacitor made from graphene/polypyrrole. Supercapacitors gain their capacitive properties from two separate mechanisms; electric double-layer capacitance (EDLC) and pseudocapacitance. 5,6,9,13,15À17 EDLC is a result of the accumulation of electrostatically charged layers at the interface between the electrode and electrolyte and is therefore greatly influenced by the surface area of the electrode material. 1,6,8À10,13,15,20 To maximize EDLC, various forms of high surface area carbon have been investigated such as carbon nanotubes, activated carbon black, and graphene. 1,6,8,12,15,17,21À25 As a prominent material, graphene (G) sheets are 2D, single-atom thick layers of sp 2 -bonded carbon. 26À29 These are of particular interest because it has been recently shown that optically transparent, flexible G films can be created while preserving G's good electrochemical properties. 15,19,28À35
