(397a) Fundamental Studies on the Origin of Reduced Graphene Oxide Enhancements in Energy Storage Applications
Graphene oxide (GO) offers unique opportunities to generate conductive composites consisting of electrochemically-active nanomaterials useful in energy storage applications. The electronegative oxygen moieties present on the GO surface provide negatively-charged species to which positive cationic precursors common to energy storage materials such as metal oxides can adsorb. This mechanism for producing electrode composites yields high surface coverage of the 2-D GO sheets. After reduction of GO to reduced graphene oxide (RGO), which can be accommodated in a multitude of ways, conductivity is restored and the active materials are in direct contact with an electron shuttle for effective delivery of electrons to otherwise poorly-conducting metal oxide intercalation materials. At the same time the drying of RGO sheets during solid electrode preparation enhances the natural wrinkling of the graphene sheets and produces a 3-D porous structure through which Li+ ions are able to more rapidly diffuse. Here we present a systematic study of the electrochemical enhancements RGO offers to electrode architectures in energy storage applications. Specifically, we build a composite electrode consisting of MnO2 nanowires and RGO and test the electrodes in lithium half-cell construct using an in-house cell design allowing for post-characterization of the electrode. Coulometric techniques were utilized to study the kinetics of the electron transfer reactions, Li+ ion diffusion and adsorption, and the electron storage capabilities of the RGO sheets. Cyclic voltammetry in conjunction with XRD also shows a self-healing mechanism for oxygen deficient sites on the MnO2 nanowires when composited with RGO. Finally, Transmission and scanning electron microscopy were used to characterize the surface morphology of the MnO2 nanowires and the RGO composite.