Graphene Composite Materials for Supercapacitor Electrodes

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Graphene Composite Materials for Supercapacitor Electrodes

John Lake1,2, Zuki Tanaka1,3, and Bin Chen1,3 1

NASA Ames Research Center, Moffett Field, CA 94035, U.S.A.

2

Department of Mechanical Engineering, Columbia University, NY, 10027, U.S.A.

3

Department of Electrical Engineering, University of California, CA 95064, U.S.A.

ABSTRACT This study presents a materials development of composite electrode materials of graphene oxide (GO) and transition metal oxide nanostructures. Reduced graphene oxide (rGO) films were obtained by electrophoretic deposition (EPD) onto a conductive substrate. Co3O4 and MnO2 nanostructures were synthesized to form composites with rGO. Graphene materials, with high electrical conductivity, high specific surface area and excellent mechanical properties are ideal for a host of electrical applications. The properties of metal oxides like Co3O4 and MnO2 has allowed for increased energy density, while rGO increases charge storage and transport in the electrical double layer at the electrode/electrolyte interface. Graphene and metal oxide composites offer increased energy density and capacitance compared with traditional double layer supercapacitors.

INTRODUCTION Electrochemical capacitors, or super- capacitors, have gained much interest as alternatives to traditional energy storage devices because of their high power capability and long lifetime. While the power density of supercapacitors surpasses that of most batteries, most commercially available batteries have a significantly higher specific energy density than supercapacitors. Supercapacitors have potential applications ranging from plug-in hybrid electric vehicles (PHEVs) to backup power sources. With the increased power demand for supercapcacitors to be used in tandem with batteries or as part of smart grids, the development of superior supercapacitors with improved energy density is of the utmost importance. Energy storage within a supercapacitor occurs either by ion adsorption (electrical double layer capacitance) or by faradic, redox reactions (pseudocapacitance). Graphene holds promise as a material for many electrical applications and has been proven as an effective material for supercapacitor electrodes due to its large surface area, high mechanical stability and electrical conductivity [4, 5]. Graphene electrodes alone allow for double layer specific capacitances of up to 135 F/g [4]. With large specific pseudocapacitances, the metal oxides MnO2 and Co3O4 allow for fast, reversible Faradic reactions at the interface of their surface and the electrolyte. Reported composites of MnO2 and Co3O4 have shown specific capacitances of up to 480 F/g at a specific current of 2.67 A/g [6].

Combining graphene with a metal oxide nanocomposite of MnO2 and Co3O4 would likely offer specific capacitances surpassing 600 F/g. Addition of an rGO layer to metal oxide composite materials would also likely provide increased cyclic stability to the metal oxide electrodes from the superior mechanical properties possessed by graphene materials. Add

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