Supercapacitors based on high-surface-area graphene

Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide. N2 adsorption-desorption measurement showed that graphene so obtained had a specif- ic surface area as high as 818 m2/g. Galvanostatic charge/discharge curves demonstrated that the as-prepared graphene exhib- ited a specific capacitance of 186.9 F/g at a current density of 0.1 A/g and that about 96% of the specific capacitance was re- tained after 2000 cycles at a current density of 5 A/g.