A novel asymmetric supercapacitor with an activated carbon cathode and a reduced graphene oxide-cobalt oxide nanocomposite anode

Co3O4-reduced graphene oxide (rGO) nanocomposites are prepared by co-precipitation of Co(OH)(2) with graphite oxide (GO) to form a Co(OH)(2)-GO precursor, followed by thermal treatment. It is found that the ratio between Co3O4 and rGO has a significant effect on their electrochemical activities. The specific capacitance of 636 F g(-1) is achieved when the mass ratio of Co3O4 to rGO is equal to 80.3:19.7. A novel asymmetric supercapacitor is further fabricated with the Co3O4-rGO nanocomposite as the anode and activated carbon as the cathode in 6 M aqueous KOH solution as electrolyte. The assembled asymmetric supercapacitor can cycle reversibly in a voltage of 0-1.5 V and exhibits a high energy density of 35.7 Wh kg(-1) at power density of 225 W kg(-1). Moreover, the asymmetric supercapacitor shows an excellent cycling stability with capacitance retention of 95% after 1000 cycles at a current density of 0.625 A g(-1). (C) 2013 Elsevier B.V. All rights reserved.