<p>Graphene, first isolated in 2004 and the subject of the 2010 Nobel Prize in physics, has generated a tremendous amount of research interest in recent years due to its incredible mechanical and electrical properties. However, difficulties in large-scale production and low as-prepared surface area have hindered commercial applications. In this dissertation, a new material is described incorporating the superior electrical properties of graphene edge planes into the high surface area framework of carbon nanotube forests using a scalable and reproducible technology.</p><p>The objectives of this research were to investigate the growth parameters and mechanisms of a graphene-carbon nanotube hybrid nanomaterial termed “graphenated carbon nanotubes” (g-CNTs), examine the applicability of g-CNT materials for applications in electrochemical capacitors (supercapacitors) and cold-cathode field emission sources, and determine materials characteristics responsible for the superior performance of g-CNTs in these applications. The growth kinetics of multi-walled carbon nanotubes (MWNTs), grown by plasma-enhanced chemical vapor deposition (PECVD), was studied in order to understand the fundamental mechanisms governing the PECVD reaction process. Activation energies and diffusivities were determined for key reaction steps and a growth model was developed in response to these findings. Differences in the reaction kinetics between CNTs grown on single-crystal silicon and polysilicon were studied to aid in the incorporation of CNTs into microelectromechanical systems (MEMS) devices. To understand processing-property relationships for g-CNT materials, a Design of Experiments (DOE) analysis was performed for the purpose of determining the importance of various input parameters on the growth of g-CNTs, finding that varying temperature alone allows the resultant material to transition from CNTs to g-CNTs and finally carbon nanosheets (CNSs): vertically oriented sheets of few-layered graphene. In addition, a phenomenological model was developed for g-CNTs. By studying variations of graphene-CNT hybrid nanomaterials by Raman spectroscopy, a linear trend was discovered between their mean crystallite size and electrochemical capacitance. Finally, a new method for the calculation of nanomaterial surface area, more accurate than the standard BET technique, was created based on atomic layer deposition (ALD) of titanium oxide (TiO2).</p> / Dissertation

<p>The primary goals of this research were to investigate the electrochemical behavior of carbon nanostructures of varying morphology, identify morphological characteristics that improve electrochemical capacitance for applications in energy storage and neural stimulation, and engineer and characterize a boron-­doped diamond (BDD) electrode based electrochemical system for disinfection of human liquid waste. </p><p>Carbon nanostructures; ranging from vertically aligned multiwalled carbon nanotubes (MWCNTs), graphenated carbon nanotubes (g-­CNTs) to carbon nanosheets (CNS); were synthesized using a MPECVD system. The nanostructures were characterized by using scanning electron microscopy (SEM) and Raman spectroscopy. In addition to employing commonly used electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), a new technique was developed to evaluate the energy and power density of individual electrodes. This facilitated comparison of a variety of electrode materials without having to first develop complex device packaging schemes. It was found that smaller pore size and higher density of carbon foliates on a three-dimensional scaffold of carbon nanotubes increased specific capacitance. A design of experiments (DOE) study was conducted to explore the parametric space of the MWCNT system. A range of carbon nanostructures of varying morphology were obtained. It was observed that the capacitance was dependent on defect density. Capacitance increased with defect density.</p><p>A BDD electrode was characterized for use in a module designed to disinfect human liquid waste as a part of a new advanced energy neutral, water and additive-free toilet designed for treating waste at the point of source. The electrode was utilized in a batch process system that generated mixed oxidants from ions present in simulated urine and inactivated E. Coli bacteria. Among the mixed oxidants, the concentration of chlorine species was measured and was found to correlate to the reduction in E. Coli concentration. Finally, a new operating mode was developed that involved pulsing the voltage applied to the BDD anode led to 66% saving in energy required for disinfection and yet successfully reduced E. Coli concentration to less than the disinfection threshold.</p> / Dissertation