Growth of Hierarchical Graphene Structures as Energy-Related Materials

Abstract

Graphene has received considerable attention due to its excellent electrical properties, high thermal conductivity, outstanding flexibility and great stiffness, Many methods such as chemical exfoliation of graphite oxide, liquid-phase ultrasonic exfoliation of graphite, epitaxial growth on SiC or metals, and chemical vapor deposition (CVD) growth on metal substrates have been exploited for the production of graphene sheets with excellent properties. Three-dimensional (3D) bi-continuous structures with controlled symmetry and periodicity have found use in many applications in photonic crystals, phononic crystals and micro-electromechanical systems. In addition, the large surface area and the availability of 3-dimensional responses to external stimuli provide further potential for using 3D structures in diverse areas of energy-related materials and tissue engineering. In particular, porous carbon materials have been suggested as effective electrodes for energy devices due to their large surface area and size tunable porosity for easy access of the electrolyte. More specifically, effective surface area and pore volume in the nanostructure provide active sites for better performance of the energy devices, which operates via a mechanism of charge-transfer at the electrochemical interface between the electrode and electrolyte. In this thesis, I studied on the direct route to producing hierarchical graphene structures of few-layer graphene grown by CVD without using flammable gas. Mesopores are formed by the loss of organic materials during the carbonization process of polymer composites and metal precursors. Carbonized carbon and reduced metal precursors in a hierarchical structures formed by the thermal annealing of the sample in a hydrogen gas environment provide a solid carbon source and a catalyst for the graphene growth during the CVD process, respectively. The outstanding properties of hierarchical graphene structures suggest the great potential of interconnected graphene networks for energy-related materials such as electrode for electrical double layer capacitor, 3D-current collector for water splitting, counter electrode for DSSCs and lithium ion battery.