Synthesis And Supercapacitive Behaviors Of Graphene-based Electrode Materials

Abstract:Supercapacitors, also well-known as electrochemical capacitors, are energy conversion and storage devices which have attracted much attention because of their ideally high power density, excellent reversibility and long cycle life. The mechanism of energy storage of supercapacitor is on the basis of electrical double layer capacitive(EDLC) and pseudo-capacitive. Graphene is endowing the carbon materials for potential application in electrochemical energy storage with various superior properties such as large specific surface area, high electrical conductivity and charge-carrier mobility, high mechanical strength and inherent flexibility. The properties of the electrode materials are important factors for the supercapacitors,where the excellent electrode materiasl show high conductivity, high surface-area, high temperature stability, controlled pore structure and relatively low cost.Dehydrated reduced graphene oxide (rGO-D) was prepared by exploiting the dehydration of concentrated sulfuric acid at different temperature. The influences of the residual oxygen functional groups and sp2domains on sulfuric acid dehydrated graphene were investigated for capacitance performance. The results showed that the amount of oxygen functionalities and newly formed sp2domains were different for rGO-D at different temperature. These unique materials are found to provide high specific capacitance and good cycling stability. The high specific capacitance of281.8F g-1is obtained from cyclic voltammetry measurement at a scan rate of10mV s-1as the sulfuric acid dehydrated graphene electrode was reduced at70℃. These promising results are attributed to the high reduction degree and sp2domains with smaller size for rGO-D, which indicate their potential application to electrochemical capacitors.Electrophoretic deposition in conjunction with electrochemical reduction was used to make flexible free-standing graphene-like films. Firstly, Graphene oxide (GO) film is deposited on graphite substrate by electrophoretic deposition method, and following by subsequent electrochemical reduction of GO to obtained high performance electrochemically reduced GO (ERGO) film. The morphology, structure and electrochemical performance of the prepared graphene-like film are confirmed with SEM, XRD and FT-IR. These unique materials are found to provide high specific capacitance and good cycling stability. The high specific capacitance of254F g-1is obtained from cyclic voltammetry measurement at a scan rate of10mV s-1. When the current density increases to83.3A g-1, the specific capacitance values still remains132F g-1. Furthermore, at a constant scan rate of50mV s-1,97.02%of its capacitance was retained for1000cycles.A series of high-quality graphene/Fe3O4nanocomposites were readily obtained by a simple one-pot hydrothermal method under mild conditions. The as-prepared graphene/Fe3O4hybrids were characterized by powder XRD, FT-IR, TEM, XPS, and TGA. The experimental results demonstrated that ferromagnetic Fe3O4nanocrystals (NCs) of5-9nm are facilely achieved and anchored onto the surface of graphene nanosheets. As an electrode material for electrochemical capacitors, the electochemical properties of graphene/Fe3O4nanocomposites were tested, and it was interesting to find that the combination of graphene nansheets with Fe3O4NCs showed much higher specific capacitances than that of either pure graphene or pure Fe3O4NCs, making them a promising electrode material for supercapacitors. Furthermore, the graphene hybrids also showed excellent long cycle life along with94%specific capacitance retained after1000cycle tests.