Mechanical Engineering ETDs

Publication Date

2-8-2011

Abstract

Two primary objectives were the basis of this research. The first objective was to synthesize a variety of carbonaceous nanomaterials using plasma torch and furnace-based expansion-reduction techniques. The second objective was to correlate the unique characteristics of these materials to their electrical properties when assembled into electrochemical double-layered capacitors (EDLCs), or supercapacitors. A microwave atmospheric plasma torch was used to produce graphene and diverse graphitic and amorphous carbon nanomaterials. Direct high-temperature conversion under an argon plasma atmosphere of various hydrocarbons, in solid, liquid, and gaseous states, yielded carbon nanoparticles, nanoparticle/sheet mixtures, and graphene respectively. Graphene was also produced using a novel furnace treatment consisting of a simple two-step process: Graphite oxide (GO) was mixed with an expansion—reduction agent (urea) that decomposed upon heating, releasing reducing gases. The mixture was then heated in an inert gas environment (N2) for a very short time and moderate temperature (600 °C). The morphologies of all products produced were studied using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), while the crystalline structure and relative percentage of crystalline material was analyzed by X-ray Powder Diffraction (XRD) and Temperature Programmed Oxidation (TPO) methods. Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC) was used to study the GO/urea mixtures decomposition-reduction process. Electron Energy Loss Spectroscopy (EELS) analysis of both samples produced using the torch and expansion-reduction methods is also presented. Characterization of the graphene samples was also performed using Raman Spectroscopy. The samples surface area and functional groups were also analyzed using BET, and point-of-zero-charge (PZC) analysis respectively. The materials produced were formed into thin-film electrodes and their capacitances and resistances were evaluated. The electrical data recorded for each material as well as the characterization of their structure was used to correlate microstructural characteristics of each material to its electrical properties as an EDLC electrode material. This work exemplifies the usefulness of the plasma torch system as a means to generate diverse material architectures difficult to obtain by alternative routes, as well as the effectiveness and value of a new expansion-reduction process in producing graphene. This study also helps to shed light on some of the mechanisms and characteristics of carbonaceous materials that contribute to their usefulness as functional materials in EDLCs.'

Keywords

carbon, supercapacitor, electrode, graphene

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Leseman, Zayd

Second Committee Member

Shen, Yu-Lin

Third Committee Member

Carpenter, Bernie

Fourth Committee Member

Chapman, David

Sponsors

Air Force Research Laboratory

Document Type

Thesis

Language

English

Download

Share

COinS