Graphene Oxide Langmuir-Blodgett Films for Capacitive Energy Storage

Abstract

Pristine graphene remains cost-prohibitive for most commercial applications. The synthesis cost of graphene oxide is several orders of magnitude lower than that of pristine graphene, but it is highly defected and decorated with oxygen functional groups. Some of the properties of graphene oxide are comparable to those of graphene (e.g. specific surface area, flexibility, and transparency), other properties are degraded (e.g. conductivity, mechanical strength), and still other properties are unique to graphene oxide (e.g. colloidal stability, surface charge, chemical pliability). Nonetheless, like graphene, many of graphene oxide's properties require that it to be used as a monolayer and not as a stacked multilayer. The Langmuir-Blodgett technique is one method to deposit monolayers of graphene oxide onto a solid substrate. In this thesis, the properties and potential applications of graphene oxide Langmuir-Blodgett films are investigated. In addition to fundamental studies of the Langmuir-Blodgett method itself (Part I), technological studies on the impact of GO monolayer morphology and chemistry on capacitive performance are presented (Part II). In Chapter 1, an introduction to graphene oxide, the Langmuir-Blodgett method, and capacitive energy storage are presented. In Chapter 2, the forces between and within graphene oxide sheets adsorbed to the air-water interface are investigated including the aggregation and clustering of GO. Chapter 3 discusses a method of GO compression at the air-water interface (``periodic pulsing compression'') which allows for measurement of the onset of elastic behavior, jamming, and ultimately out-of-plane deformations. This method is the first demonstration in the literature of nano-scale control over the surface roughness of deposited Langmuir-Blodgett films. In chapter 4, GO monolayers are wrinkled and folded using the Langmuir-Blodgett technique. Stacked monolayers of nano-folded GO exhibit high volumetric capacitance as a supercapactior electrode. Chapter 5 introduces plasma-treatment as a technique to modify the oxygen content of GO to induce high-rate pseudocapacitiance. Finally, Chapter 6 and 7 present future research ideas for periodic pulsing compression, nano-folded GO, and plasma-activated GO, as well as a synthesis of these findings in a broader context.