Controllable Preparation And Electrochemical Performances Of Holey Graphene/Metal Oxide Hybrids

Graphene possesses unique 2-dimensional structure, remarkable physical and chemical properties and great application potentials, which make it the most promising one in the family of carbon materials. However, pure graphene failed to meet demands of various areas, besides, the graphene layers tend to restack and aggregate, which strongly restricts the practical application of graphene. Recently. numerous graphene derivatives and composites prepared by doping, modification. assembling and hybridization emerged, which contribute in enriching and optimizing the properties of graphene-based materials and enhance their performances, consequently, promote the practical application of graphene. As a new graphene derivative, holey graphene has attracted lots of attention due to its 2-dimensional layered structure, ultrahigh specific surface area, opened band gap and abundant active sites. This thesis focuses on holey graphene, confirmed the function of KOH activation and catalytic oxidation on inducing holes into graphene layers, developed kinds of preparation methods for two-dimensional and three-dimensional holey graphene-based materials, studied on the synthesis mechanism and morphology controlling of holey graphene, discussed the electrochemical performances of holey graphene-based materials, especially the performances of holey graphene/metal oxide hybrids as oxygen reduction catalysts, supercapactor electrode, lithium-ion battery anode and Li-S battery cathode materials.A hybrid of holey graphene and Mn3O4 nanoparticles was prepared by a one-step in-situ process. Graphene oxide and KMnO4 were utilized as precursors, the formation of holey structure was accompanied with Mn3O4 nanoparticles through a high temperature promoted catalytic oxidation between graphene sheets and KMnO4. The density and sizes of holes and particles could be controlled by altering the calcination temperature, calcination time and manganese content. The functional groups were certified to be responsible for the pore formation, pores did not appear on the layers of products obtained by replacing graphene oxide with graphene. The particle was always surrounding each generated hole, this unique structure promoted the diffusion of electrolyte and oxygen moleculars, benefited the catalytic performance of Mn3O4 nanoparticles, moreover, strong interaction existed between the formed Mn3O4 nanoparticles and holey grahene sheets. The hybrid of holey graphene and Mn3O4 exhibited enhanced catalytic activity and efficiency towards oxygen reduction reaction and much better performance as supercapacitor electrode while comparing with the hybrid of graphene and Mn3O4.Furthermore, we combined inducing holes into graphene layers with the assembly of three-dimensional graphene macroforms, successfully fabricated materials exhibiting holes not only in the layers but also between the layers of graphene. Via the combination of hydrothermal method with KOH activation, we prepared activated three-dimensional graphene macroform with holey sheets, For the purpose of optimizing the composition, structure and properties of holey graphene-based materials, we prepared a hybrid of 3-dimensional holey graphene and Fe2O3 nanoparticles via a combination of the hydrothermal method and the catalytic oxidation. This hybrid comprises holey graphene and Fe2O3, combines holey sheets and nanoparticles with 3-dimensional porous structure, possesses high electron/ion transport efficiency, abundant active sites and high electrochemical activity, consequently, it revealed high performance as oxygen reduction catalyst, lithium battery anode and Li-S battery cathode materials.A graphene/Mn composite hydrogel was prepared via mild heating treatment.The amount of KMnO4 and graphene oxide had a major influence on the forming and morphology of graphene/Mn hybrid. The research system in which a hydrogel was formed possessed a much lower evaporation rate than several comparing systems that lacked the forming of hydrogels, moreover, the evaporation rate decreased with the increasing of the hydrogel size.