Low Temperature Plasma-Assisted Synthesis Of Graphene-Based Composites And Their Electrochemical Performance

Graphene is a new member in the family of carbon nanomaterials, it has received increasing interest from researchers worldwide due to its unique electronic, mechanical, optical and thermal properties. Graphene based materials have potential applications in the field of electronics, energy storage, catalysis and biomedicine, etc. Low-cost and environment-friendly route for large scale preparation of graphene-based materials is desirable. In the present thesis, controllable reduction of GO is successfully achieved by dielectric barrier discharges (DBD) plasma technique, and the effects of discharge conditions on the structures, surface properties and electrochemical performance have been systematically investigated. Moreover, the reduced graphene oxide (rGO) decorated with the metals or metal oxides, such as Pt, Ru, PtRu, Ni, NiO nanoparticles, Fe3O4nanorods and NiO nanosheets, have been fabricated by the combination of DBD and aqueous precipitation. Finally, we study the energy storage performance of these materials in supercapacitor and lithium ion battery. The results are summarized as following:rGO was controllably fabricated by simultaneously exfoliating and reducing GO under DBD plasma with various working gases, including H2(reducing), Ar (inert) and CO2(oxidizing). The deoxygenation degree of GO is related to the type of working gases while regardless of the bulk temperature during plasma discharge, which implicates a high-energy electron/ion bombardment deoxygenation mechanism. Acting as electrode materials in a supercapacitor cell with KOH electrolyte, the rGO materials from various plasmas exhibit high specific capacitance and good electrochemical stability.Taixi coal (TX) derived rGO (TX-C-rGO) and graphene-noble metal composites were synthesized by means of catalytic graphitization (TX-C-G), chemical oxidation (TX-C-GO), and DBD plasma-assisted deoxygenation. It is found that the graphitization degree of the coal-derived carbon remarkably affects the properties of TX-C-GO obtained from chemical exfoliation, and high crystallinity of TX-C-G is essential for the preparation of high-quality TX-C-rGO. TX-C-rGO decorated with highly dispersed noble metallic nanoparticles (NP/rGO) on their surface was successfully fabricated via simultaneous reduction of TX-C-GO and noble metal salts by H2DBD plasma technique. The electrochemical performance of the TX-C-rGO as electrode in supercapacitor and the catalytic activities of NP/rGO composites in selective reduction of nitrogen oxides (NOx) demonstrate that graphene and its composites fabricated by the alternative approach from coal have promising potential in energy storage and environment preservation.A general green, low-cost and fast method for the fabrication of Ni/NiO nanoparticles (NP) and NiO nanosheets (NS) decorated rGO by the assistance of low temperature plasma technique has been developed. Ni or NiO can be selectively produced from the same nickel precursor depending on the plasma atmospheres employed, and rGO from GO simultaneously during the plasma process. NiO-NP/rGO and NiO-NS/rGO composites were used as electrode material in supercapacitor and lithium ion battery, respectively, and they exhibit excellent electrochemical performance. These fascinating performances can be attributed to their enhanced electron transport rate, high electrolyte contact area, and structural stability.A novel composites consisting of porous rod-shaped Fe3O4anchored on reduced graphene oxide (Fe3O4/rGO) were fabricated by controlling the in situ nucleation and growth of β-FeOOH onto the graphene oxide (β-FeOOH/GO) and followed by DBD hydrogen plasma treatment. Such well-designed hierarchical nanostructures are beneficial for maximum utilization of electrochemically active matter in lithium ion batteries and display superior Li uptake with high reversible capacity, good rate capability, and excellent stability, maintaining890mAh g-1capacities over100cycles at a current density of500mA g-1. Even cycled at very high current densities of1000-3000mA g-1, it may still deliver high reversible capacities in the range of520-700mAh g-1due to the enhanced structural stability, electronic conductivity and kinetics for lithium storage.