Preparation of Functionalized Graphenes and Their Performance for Corrosion Resistance and Synthesis of Vanadium Nitridecarbon Nanofiber Mats and Their Application for Asymmetric Supercapacitor Electrodes

Carbon materials have been researched in a wide range of applications, including energy storage, corrosion protection, catalyst support, etc. Though many people have studied properties of carbon with/without modification, research in the synthesis of functionalized carbon and carbon composites therefrom will be important. This dissertation outlines the synthesis of functionalized graphene, development of graphene composites, and metal nitride-carbon nanofiber composites and their application for electrode for super-capacitor. Graphene is single layer carbon-based material known for its multifunctional properties (e.g. hydrophobicity, mechanical strength, etc.). This work studies application of graphene through functionalization of mechanically exfoliated graphene and functionalized graphene use for corrosion resistance. Functionalization of graphene is first discussed in the eco-friendly synthesis of aminated mechanically exfoliated graphene (MEG). Here we are able to directly functionalize MEG with amine groups using glycerol as the reaction medium and urea as the amine source.

The aminated MEG (AG) also showed enhanced dispersion stability in organic solvents and aquous-solvent mixtures for >60 days. In the second area, we discussed how functionalized graphenes affected surface properties and corrosion resistance when composited with a polymer coating. Graphene, aminated graphene (AG), and fluorinated graphene (FG) were studied for corrosion resistance. Both AG and FG exhibited enhanced corrosion resistance when composited with a 2K urethane coating. Composite coating with FG showed a 94% increase in corrosion resistance versus graphene at a concentration of 4% by weight of solids. These materials also enhanced the surface properties of the coating. Electrochemical analysis of composite coatings showed that through inclusion of functionalized graphenes (AG or FG), barrier and adhesion properties were strengthened. Both FG and AG composite coatings showed an increase in contact angle versus graphene, with FG resulting in a hydrophobic surface (>90o ) at 4wt%. This project shows a step towards the potential removal of sacrificial zinc as a barrier for corrosion resistance of steel substrate. The increase in energy consumption over the last decade has led to research in the development of alternative energy storage devices which can meet the demand. Supercapacitors have garnered increased attention in this field due to their ability to provide high power and high energy. Electrodes within these devices can consist of two different materials, carbon or pseudocapacitive material. While carbon-based supercapacitors, or EDLCs, can provide high power density, they suffer from low energy densities. This has led researchers to study composite, or hybrid electrodes which combine the high power EDLC material with a high energy pseudocapacitive material (e.g. metal oxide or metal nitride). In the third area, we

assembled and tested hybrid-asymmetric devices using activated vanadium nitride-carbon nanofiber (VN-CNF) electrodes. The VN was made using vanadium oxide (V2O5) nanoflowers by a new synthesis method. Composite electrodes were made by electrospinning of a poly(acrylonitrile-co-itaconic acid) (PANIA) solution with the vanadium oxide (V2O5) nanoflowers dispersed within it to produce freestanding mats. VN-CNF freestanding mats were used as anode material and CNF as the cathode when assembling the device. Ionic liquid electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) with 0.5M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used, which widens the operating voltage window (>3.5V) compared with aqueous (e.g. KOH or Na2SO4) or organic electrolytes (e.g. TEA-BF4 in ACN). Chapter 1 introduces the material graphene, its properties, and methods of synthesis. In this section we also review methods of functionalization and application in the field of corrosion protection. Chapter 2 describes the eco-friendly method of functionalization of mechanically exfoliated graphene (MEG) with amine groups and the effect of these groups on dispersion stability in organic solvents and aqueous-solvent mixtures are studied. Chapter 3 studies the effect of graphene, aminated graphene (AG), and fluorinated graphene (FG) on surface properties and corrosion resistance when composited with a urethane coating. Contact angle measurements and electrochemical analysis were performed to determine which graphene and concentration provides best corrosion resistance.

Chapter 4 introduces supercapacitors and the concepts behind the different types. This section describes charge storage mechanisms of the pseudocapacitors and discusses different aspects of metal oxides and nitrides. Chapter 5 describes the preparation of vanadium nitride-carbon nanofiber (VN-CNF) composite electrodes and analysis of their electrochemical properties. Charge contributions and storage mechanisms for each sample was studied to understand the mechanism in which their charge is stored (e.g. intercalative or pseudocapacitive/capacitive).