Reduced graphene oxide for energy storage

Abstract

Graphene, a one-atom-thick two-dimensional (2D) material comprising sp2-hybridized carbon atoms, is expected for various applications. However, the disadvantages of low production efficiency and high cost limit the industrialization of graphene. Therefore, recent efforts have been devoted to developing graphene derivates with high yield and low cost. One typical example is reduced graphene oxide (rGO). The rGO is made by the removal of oxygen functional groups (epoxy, hydroxyl, and carboxyl groups) within graphene oxide (GO) which is usually prepared via the oxidization of bulk graphite. With a restoration of sp2-bonded carbon from sp3 carbon, the obtained rGO shows good electronic and mechanical properties, which render rGO a promising candidate in various fields, such as energy storage, sensors, and water purification. The primary aim of this thesis is to study the electrochemically reduced graphene oxide (ERGO) membranes in various aspects, such as the structure, properties and the performances in energy storage. The ERGO membrane was prepared by the potential-assisted reduction of vacuum filtrated GO film. The sp3 carbons of GO sheets were recovered, and oxygen functionalities were removed through gaining electrons. This was evidenced by the SEM image that the thickness of ERGO membrane is lower than that of GO. The resistivity of ERGO measured by the four-probe method was declined, and the capacitance showed an increase after the electrochemical reduction. In addition, the thesis investigated the porous rGO electrode which was prepared via the hydrothermal reduction approach. The rGO electrode showed stable electrochemical performance with a supercapacitance value of 195 F g-1 at 1 mV s-1 and low real impedance with good stability and integrity after 4000 cycles of continuous charge-discharge in 1 M KOH electrolyte. With the characterization from XRD, SEM, Raman, this performance is attributed to the unique architecture of the rGO based electrodes, which are composed of nano-channels between the sheets that allow rapid diffusion of charge carriers and ions for electrochemical interactions. The observations shed light on the structure-stability-performance trade-off in rGO and layout the foundation for further investigations on their sustainable utilization in energy storage applications.