Synthesis Of Composite Of Transition Metal Oxide And Graphene And Their Supercapacitor Properties

Supercapacitor also called electrochemical capacitor, is a new type energy storage device with a lot of attractive properties including high power density, long cycle life, good safety, no pollution. Supercapactiors have huge potential applications in electric devices, bridging the traditional capacitor and battery. Graphene, a two-dimensional and single atomic layered carbon material, has a lot of impressive properties, such as large specific surface area, high electric conductivity, superior mechanical stability. Transition metal oxide, used as electrode material of supercapacitor, has been investigated a lot due to its large pseudocapacitance. By combining nanostructured metal oxide with graphene, both the electric double layer capacitor of graphene and the pseudocapacitor of metal oxide can be utilized.In this work, a simple solution method was developed to prepare the composite of transition metal oxide and graphene A3O4/GNS (where A represents Mn, Fe, Co). The formation of A3O4nanoparticle and the reduction of graphene oxide were carried out simultaneously. The electrochemical properties of A3O4/GNS were tested. The as-prepared MnO4/GNS, Fe3O4/GNS and Co3O4/GNS nanocomposites exhibited large specific capacitance (708,358and240Fg-1, respectively), high energy density (20,10and7Wh kg-1, respectively) and good electrochemical stability (retention of73%,67.8%and95.8%, respectively, after1000charge-discharge cycles). The excellent electrochemical performance of the A3O4/GNS nanocomposites indicated great potential in the application in supercapacitors.Then the composite of graphene and CoAl layered double hydroxide (RGO/LDH) was prepared by a solution method. An asymmetric supercapacitor (RGO/LDH//AC) was assembled with RGO/LDH as positive electrode and activated carbon as negative electrode. RGO/LDH//AC capacitor exhibited excellent electrochemical properties with a maximum energy density of35.5Wh kg-1. Moreover, the devices also showed a long cycle life of～90%retention after6000cycles.