Graphene nanoplatelets (GnP) are platelet shaped particles of graphite less than 5 nanometer in thickness and up to 50 microns in diameter consisting of a few layers of graphene produced by the exfoliation of graphite. The resulting GnP has a high open surface area consisting predominantly of the graphene basal plane. High open surface area coupled with the properties of graphene is an important criterion for electrodes in many electrochemical energy storage technologies as it provides many electrochemical reaction sites. Unique platelet morphology of GnP offers the potential to structure self-standing electrodes by doing away with inactive components such as current collectors. Surface modification of GnP through the deposition of metal nanoparticles on high open surface area has the potential to enhance the energy storage capacity due to the participation of two different components. In the first part of this research, GnP with different surface area, particle size and structure combined with an organic electrolyte has been investigated as a Lithium-air cathode. GnP with a surface area of 750 m2/gm and submicron particle size was found to deliver a higher discharge capacity with little overpotential compared to GnP with a surface area of 120-150 m2/gm and 15 micron average particle size. Binder free, self-standing, paper-like GnP electrodes have been investigated as higher energy density alternative to metal current collector cathodes. A hybrid bilayer GnP paper composed of two types of GnP was found to counter the negative effect of higher electrode loading on discharge capacity by enhancing the net surface area of an electrode.High surface area electrodes are an important criterion for high specific capacitance. The second part of this research investigated GnP as an electric double layer capacitor (EDLC) electrode material in an aqueous electrolyte. A hybrid bilayer GnP paper was found to retain near-ideal double layer capacitive characteristics at a high scan rate of 1 V/sec. Specific capacitances of 66 F/gm and 27 F/gm were obtained at a current rate of 1 A/gm from 750 m2/gm GnP and the hybrid bilayer GnP paper respectively. The small equivalent series resistance (ESR) and charge transfer resistance (Rct) of this GnP paper electrode was found to be the cause of this desirable behavior. The third part this research investigated a GnP composite system consisting of high open surface area GnP combined with metal oxides. XRD and Scanning Electron Microscopy found that when GnP substrate (120-150 m2/gm, 15 micron average particle size) is introduced in the wet-chemical synthesis of MnO2, agglomeration is significantly reduced while retaining the crystal structure. The same observation was made for two types of manganese oxides, birnessite-MnO2 and gamma-MnO2, both of which are of interest as pseuodocapacitor electrode materials. The introduction of polyethylenimine surfactant in the system changes manganese oxide morphology from a continuous ribbon-like structure to nanoparticle clusters and the oxidation state of manganese is reduced to form Mn3O4. The polymer acts both as a capping agent to restrict crystal growth and as a reducing agent. The Mn3O4-GnP composite has potential as a higher performing Lithium-ion battery anode.
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