Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Graham, Samuel; Committee Member: Garimella, Srinivas; Committee Member: Kippelen, Bernard; Committee Member: Melkote, Shreyes; Committee Member: Ready, Jud. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The research to date, of transcutaneous electric nerve stimulation on cutaneous blood flow, is equivocal. The purpose of this report is to review the TENS body of knowledge, in particular synthesizing the literature on acupuncture stimulation of cutaneous blood flow with the two fold goal of creating a protocol to increase skin blood flow through the exogenous application of electrical stimulation, as well as creating an engaging engineering challenge for high school anatomy and physiology students. The hypothesis developed was TENS stimulation with electrode placement on specific acupuncture points would influence cutaneous blood flow as measured using laser Doppler flowmetry. The findings of this project did not support the hypothesis of TENS or Interferential electrical stimulation, in combination with acupuncture points or not, influencing skin blood flow. Perhaps this is due to the physiological differences between glabrous and non-glabrous skin and the different electrical resistances of each dermal layer, nerve stimulation, age and gender of subject or some combination thereof. These equivocal findings may also be the result of inconsistencies in testing protocols, such as subject preconditioning or not, subject’s position during administration of stimulation, electrode size and placement to name a few. Ultimately, this report provides a summary of the research to date, as well as outlining how this research could be adapted to supply engaging bio engineering challenges in the classroom including challenges to develop a model for delivering current to muscle; develop a model for skin blood flow management to name a few. / text

Growing environmental concerns and increasing demand for energy have stimulated extensive interest in electrical energy storage. Li-air batteries are appealing in this regard as they offer much higher energy density than the current Li-ion batteries, but the nonaqueous Li-air batteries suffer from poor cycle life arising from electrolyte decomposition and clogging of the air electrode by insoluble discharge products. Interestingly, hybrid Li-air batteries in which a solid electrolyte separates the lithium-metal anode in an aprotic electrolyte from the air electrode in an aqueous catholyte could overcome these problems. Lots of efforts have been made on developing efficient bifunctional catalysts to lower the overpotential and improve the stability of hybrid Li-air batteries, but the cycle life is still limited. This dissertation focuses on the development of advanced cell configurations and high-performance catalysts for hybrid Li-air batteries. First, a buffer catholyte solution with a moderate pH, based on phosphoric acid and supporting salts, has been developed to keep the solid electrolyte stable and reduce the internal resistance and overpotential. With a high operating voltage and the utilization of all the three protons of phosphoric acid, the buffer catholyte enables a Li-air cell with high energy density. Further increase in power density has been realized by increasing the solid-electrolyte conductivity and operating temperature to 40 °C. The biggest challenge with Li-air cells is the large overpotentials associated with the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Noble-metal-free NiCo₂O₄ nanoflakes directly grown onto a nickel foam (NCONF@Ni) has been found to exhibit high OER activity that is comparable to that of the expensive, noble-metal IrO₂ catalyst. Furthermore, a novel 3-D O- and N-doped carbon nanoweb (ON-CNW) has been developed as an inexpensive, metal-free catalyst for ORR. With a hybrid Li-air cell, the ON-CNW exhibits performance close to that of commercial Pt/C. In addition, a novel hybrid Li-air cell configuration with decoupled ORR and OER electrodes has been developed. The hybrid Li-air cell with decoupled ORR and OER electrodes eliminates the degradation of ORR catalysts and carbon support in the highly oxidizing charge process and leads to high efficiency with good cycle life. / text

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This dissertation explores the use of nanocarbons both as conductive supports for redox enzyme electrochemistry and as electrocatalytic components for the nonmediated detection of biogenic analytes. More specifically, the influence of nitrogen doping of these nanocarbons (referred to herein as nitrogen-doped carbon nanotubes, or N-CNTs) on their bioelectrocatalytic performance is studied through direct enzyme adsorption and exploitation of the N-CNTs' inherent reactivity toward H₂O₂ to create H₂O₂-based sensing strategies. Both nondoped CNTs and N-CNTs may be effectively incorporated into biogenic sensing assemblies, as demonstrated herein using a variety of electrochemical techniques. Chapter 1 gives a general overview of the scope of this research and describes previous studies conducted within our laboratories that demonstrate our CNTs' promise as biogenic electrode materials. Chapter 2 describes the chemical vapor deposition (CVD) method used to prepare both CNTs and N-CNTs and establishes their suitability for use in the detection schemes outlined in later chapters through long-term stability studies. Additionally, the redox activity of Fe nanoparticles entrapped in the CNTs as a result of this CVD growth process is examined using a host of electrochemical experiments. Importantly, the data presented in this chapter show that these Fe particles do not explain the observed electrocatalytic response of the CNTs. Chapter 3 explores the direct adsorption of horseradish peroxidase (HRP) at both nondoped and N-CNTs. Spectroscopic and electrochemical assays are used to compare the extent of HRP enzymatic activity upon immobilization at both types of CNTs. Both types of HRP/CNT composites are then utilized in a quantitative H₂O₂ sensing strategy. Chapter 4 discusses the intrinsic reactivity of N-CNTs toward H₂O₂. Koutecky-Levich plots are used to demonstrate differences in H₂O₂ consumption mechanisms between NCNTs and traditional peroxidases. By replacing HRP with N-CNTs in an amperometric glucose detection scheme, the versatility of N-CNTs as a peroxidase substitute for biogenic analyte detection is demonstrated. Chapter 5 outlines future directions for this research, including possible strategies for improving electron transfer between HRP and both types of CNTs. This chapter also presents a newly developed, mediated oxidase-substrate electrochemical detection method that can easily be modified to incorporate CNTs.

M. Tech. Department of Chemical, Metallurgical and Materials Engineering. / Discusses how to synthesize a titanium-manganese oxide composite electrode with improved supercapacitive properties. The research aim was achieved through the following objectives: 1. the mechanisms of the synergistic incorporation of manganese oxide for improving the supercapacitive properties of titanium oxide electrodes. 2. Investigate possible metallurgical interactions and phenomenon during the sintering of the composite. 3. Investigate the electrochemical characteristics of titanium-manganese composite electrodes.

The current treatment of water contaminated with organic compounds includes adsorption, air stripping, and advanced oxidation processes. These methods large quantities of water and require excessive energy and time. A novel treatment process of concentrating and then electrochemically oxidizing compound would be a more feasible practice. This research investigated the oxidative destruction of perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate (PFBS) and trichloroethene (TCE) at boron-doped diamond film electrodes and the adsorption of PFOS and PFBS on granular activated carbon and ion exchange resins.Experiments measuring oxidation rates of PFOS and PFBS were performed over a range in current densities and temperatures using a rotating disk electrode (RDE) reactor and a parallel plate flow-through reactor. Oxidation of PFOS was rapid and yielded sulfate, fluoride, carbon dioxide and trace levels of trifluoroacetic acid. Oxidation of PFBS was slower than that of PFOS. A comparison of the experimentally measured apparent activation energy with those calculated using Density Functional Theory (DFT) studies indicated that the most likely rate-limiting step for PFOS and PFBS oxidation was direct electron transfer. The costs for treating PFOS and PFBS solutions were compared and showed that PFOS is cheaper to degrade than PFBS.Screening studies were performed to find a viable adsorbent or ion exchange resin for concentrating PFOS or PFBS. Granular activated carbon F400 (GAC-F400) and an ion exchange resin, Amberlite IRA-458, were the best methods for adsorbing PFOS. Ionic strength experiments showed that the solubility of the compounds affected the adsorption onto solid phases. Regeneration experiments were carried out to determine the best method of recovering these compounds from the adsorbents; however, the compounds could not be effectively removed from the adsorbents using standard techniques.The electrochemical oxidation of trichloroethene (TCE) at boron-doped diamond film electrodes was studied to determine if this would be a viable degradation method for chlorinated solvents. Flow-through experiments were performed and showed TCE oxidation to be very rapid. Comparing the data from the DFT studies and the experimentally calculated apparent activation energies the mechanism for TCE oxidation was determined to be controlled by both direct electron transfer and oxidation via hydroxyl radicals.

The aim of this thesis is the development of solid contact ion selective electrodes, ISEs, where the transducer layer is made of a network of carbon nanotubes.Potentiometric classical ion selective electrodes (ISEs) have been used for analytical applications since the beginning of 1900's. Determination of pH by a glass membrane ion selective electrode emerged at the beginning, being the first ISEs developed. pH glass electrode is still one the most useful and robust sensors for routine measurements both in laboratories and industries.Throughout the years, new technologies, ideas and designs have been developed and incorporated successfully in the potentiometric fields so as to provide answers to the new society's needs. Therefore, the ion selective electrodes developed in this thesis are a step further in the progress of ISEs and must be considered as products of the scientific envisioning, growth, and interdisciplinary cooperation of many research teams over many years of continuous efforts. The sensing part can be regarded nowadays as well developed, although it has been during only the last few years when considerable improvements have taken place in the development of new polymeric membranes, ionophores and lipophilic ions. Moreover, the understanding of the theoretical sensing mechanism has been a powerful solid backbone in the rise of ISEs. Miniaturization of classical ISEs requires making all solid contact electrodes to avoid the intrinsic drawbacks of the inner solution. In this manner, the transduction layer has been the focus of attention for the two last decades. New solid contact transducers having the capacity to convert an ionic current into an electronic current have been emerging. Within them, conducting polymers have played an important role in the transduction of the potentiometric signal, being the most used in solid contact ion selective electrodes (SC-ISEs) up to now. However, the behaviour of conducting polymers can be further improved. For instance, their sensitivity to light one of main operational issues yet to be solved.In the present context of searching for new materials able to transduce potentiometric signals we selected and tested carbon nanotubes (CNTs). CNTs, which were rediscovered by Ijima in 1991, display excellent electronic properties in terms of signal transduction. In addition, due to their chemical reactivity CNTs can be easily functionalized with receptors or other functional groups. In fact, depending on the type of functionalization the macroscopic and microscopic properties of CNTs can be drastically changed. This nanostructured material had not been used previously as a solid contact material in ISEs.The main aim of this thesis is to demonstrate that CNTs can act as a clean and efficient transducer in SC-ISEs overcoming the drawbacks displayed by the previously assayed solid contact materials. The developed electrodes were used in different conditions to determine several ions in different sample types, demonstrating the capabilities of this nanostructured material.The thesis has been structured in different chapters, each one containing the following information:· Chapter 1 provides a short historical overview of potentiometric ISEs. The evolution from the "classical ISEs" to the SC-ISEs is briefly illustrated. Once the motivation for thesis is described, the general and specific objectives of the thesis are reported.· Chapter 2 reports the scientific foundations of the developed electrodes. All components of the ISE, sensing layer, transducers and detection systems are introduced. Analytical performance characteristics of ISEs are also described.· Chapter 3 corresponds to the experimental part. Reagents, protocols, procedures and instruments used in the thesis are reported.· Chapter 4 provides the demonstration that CNTs can act as a transducer layer in SC-ISEs. The first SC-ISEs based on CNTs are characterized by electrochemical and optical techniques.· Chapter 5 contains the experimental results that lead to the elucidation of the possible transduction mechanism of CNTs in SC-ISEs. Electrochemical impedance spectroscopy (EIS) is employed as the main characterization technique. · Chapter 6 is composed of four sections reporting different analytical applications. In the first section, the common pH electrode is developed using a solid contact technology based on CNTs. In the second section, the development of SC-ISEs based on a new synthetic ionophore selective to choline, and CNTs as transducers is shown. In the third section, watertight and pressure-resistant SC-ISEs based on CNTs are developed and tested in aquatic research to obtain information about the gradient profiles along the depth of the lakes. In the fourth section, SC-ISEs based on CNTs are adapted for the on-line control of a denitrification catalytic process.· Chapter 7 reports the possibilities of miniaturization of the SC-ISEs based on CNTs to reach a nanometric electrode. Potentiometric and optical characterizations are described in this section. Moreover, a discussion about the limitations of the real miniaturization in potentiometry is undertaken.· Chapter 8 points out the conclusions of the thesis. In addition, future prospects are suggested.· Finally, several appendices are added to complete the doctoral thesis. / El principal objetivo de esta tesis es el desarrollo de electrodos selectivos de iones de contacto sólido, ESIs-CS, utilizando como capa transductora una red compuesta de nanotubos de carbono.Los electrodos potenciométricos selectivos de iones han sido utilizados en aplicaciones analíticas desde comienzos de 1900. La determinación de pH mediante electrodos de vidrio selectivo de iones fue el primer ESI desarrollado. Hoy en día, el electrodo de vidrio para la determinación de pH es todavía uno de los más útiles y robustos sensores utilizados en mediciones rutinarias tanto en laboratorios como en industrias.A lo largo de los años, nuevas tecnologías, ideas y diseños han sido desarrollados e incorporados satisfactoriamente en el campo potenciométrico proporcionando soluciones a las necesidades en continua evolución de la sociedad. De esta manera, los electrodos selectivos de iones desarrollados en esta tesis son un paso más en el progreso de los ESIs y deben ser considerados como el producto de una sólida base científica, del crecimiento y de la cooperación interdisciplinaria de diversos grupos de investigación durante varios años.La parte del sensor donde tiene lugar el reconocimiento químico y donde se genera el potencial dependiente de la muestra en estudio en los ESIs se puede considerar, en estos días, ampliamente desarrollada, aunque considerables mejoras han tenido lugar durante los últimos años, especialmente en el desarrollo de nuevas membranas poliméricas, ionóforos e iones lipofílicos. Sobretodo, el estudio y la comprensión del mecanismo teórico del sensor ha sido muy importante en el crecimiento y desarrollo de los ESIs.El concepto de electrodos selectivos de iones de estado sólido surge como requisito vital para evitar las intrínsecas desventajas de la solución interna, en el proceso de miniaturización de los ESIs clásicos. De esta forma, la capa transductora ha sido el principal punto de atención durante dos décadas. Así, nuevos transductores de contacto sólido con la capacidad de convertir una corriente iónica en una corriente electrónica han sido desarrollados. Entre ellos, los polímeros conductores han jugado un importante papel en la transducción de la señal potenciométrica, siendo éstos los más empleados en los electrodos selectivos de iones de contacto sólido (ESIs-CS). Sin embargo el comportamiento de los polímeros conductores puede ser mejorado. Por ejemplo, la sensibilidad hacia la luz de estos materiales es un inconveniente todavía no resuelto. En este contexto de investigación de nuevos materiales capaces de actuar como transductor de una señal potenciométrica, se han escogido y estudiado los nanotubos de carbono (NTCs) como transductores. Los NTCs fueros redescubiertos por Ijima en 1991, y muestran excelentes propiedades electrónicas en términos de traducción de señal. Además, debido a su reactividad química, los NTCs pueden ser fácilmente funcionalizados con receptores u otros grupos funcionales. De hecho, sus propiedades macroscópicas y microscópicas pueden ser afectadas drásticamente dependiendo del tipo y grado de funcionalización. Este material nanoestructurado no había sido previamente utilizado como transductor en ISEs.El principal propósito de esta tesis es demostrar que los nanotubos de carbono pueden actuar de forma eficiente como transductor en electrodos selectivos de iones de estado sólido logrando vencer las desventajas de los transductores previamente mencionados. Los electrodos desarrollados fueron usados en diferentes condiciones para determinar distintos iones en diversos tipos de sistemas, demostrando las extraordinarias capacidades de este material nanoestructurado. Esta tesis ha sido estructurada en capítulos que contienen la siguiente información:· El Capítulo 1 proporciona una breve visión histórica de lo electrodos potenciométricos selectivos de iones. Se ilustra la evolución desde los "clásicos ESIs" hasta los actuales "ESIs-CS". Además se señalan en esta sección los objetivos generales y específicos. · El Capitulo 2 contiene las bases científicas de los electrodos desarrollados. Se introducen todos los componentes que integran un ESI, tales como: capa reconocedora, capa transductora y sistema de detección. A continuación se describen los parámetros analíticos de calidad de los ESIs. · El Capitulo 3 describe la parte experimental. Se recogen los reactivos, protocolos, procedimientos e instrumentos usados a lo largo de la tesis.· El Capitulo 4 provee de la demostración de que los NTCs pueden actuar eficientemente como capa transductora en SC-ISEs. Se caracteriza el primer ESI-CS integrado por NTCs mediante técnicas ópticas y electroquímicas.· El Capitulo 5 contiene los resultados experimentales que permiten la posible elucidación del mecanismo de transducción de los NTCs en los ESIs-CS. La Espectroscopia de Impedancia Electroquímica (ESI) es utilizada como la principal técnica de caracterización. · El Capitulo 6 está integrado por cuatro secciones con diferentes aplicaciones analíticas. En la primera sección, se desarrolla un electrodo de pH que usa NTCs como nueva tecnología transductora en ESIs-CS. En la segunda sección se muestra el desarrollo de un ESI-CS integrado por un ionóforo sintético selectivo a colina, y NTCs como transductores. En la tercera sección, ESIs-CS basados en NTCs, resistentes a altas presiones y totalmente herméticos, se desarrollan y prueban en investigaciones acuáticas con la finalidad de obtener información sobre los gradientes de concentración de iones en función de la profundidad de un lago. En la cuarta sección ESIs-CS basados en NTCs se adaptan para el control on-line de un proceso catalítico de desnitrificación.· El Capitulo 7 presenta la posibilidad de la miniaturización de los ESIs-CS basados en NTCs logrando obtener un electrodo nanométrico. Se muestran en esta sección la caracterización óptica y potentiométrica. Además, se discuten las limitaciones de la miniaturización real de los ESIs en potenciometría.· El Capitulo 8 contiene las conclusiones de la tesis. Adicionalmente, se sugieren las perspectivas futuras del trabajo presentado.· Finalmente, se añaden algunos apéndices como complemento de la tesis doctoral.

A novel method to detect and quantify the growth of the solid electrolyte interphase (SEI) on battery electrode materials using in-situ spectroscopic ellipsometry (SE) is presented. The effects of additives in 1 M LiPF6/EC:DEC (1:2) electrolyte on the SEI were studied. Thin film electrodes of a-Si, Ni, and TiN were prepared by magnetron sputtering for use with a custom-designed tubular in-situ electrochemical cell. Li/a-Si and Li/Ni in-situ cells in 0.1 M LiPF6/EC:DEC (1:2) were studied by galvanostatic chronopotentiometry. Large changes in the ellipsometric parameters, ? and ?, were observed for both materials. These changes were closely related to the state of charge of the in-situ cell. The formation of an a-LixSi alloy, the formation of an SEI layer, or both contributed to these large changes for a Li/a-Si in-situ cell. For a Li/Ni in-situ cell, a thin transparent surface layer was observed. The surface layer, presumably made from SEI species and species from the displacement reaction between NiO and Li, increased to roughly 17 nm during the first discharge. During the first charge, the surface layer thickness decreased to roughly 5.5 nm and could not be removed, even at high potentials. The effect of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) additives on SEI formation were studied using a Li/TiN in-situ cell in 1 M LiPF6/EC:DEC (1:2) by potentiostatic chronoamperometry. SEI thicknesses for cells containing no additives, VC, and FEC were roughly 18 nm, 25 nm and 30 nm, respectively, after a 10 h hold at 0.1 V. SE is a useful technique for measuring thin film growth in-situ on electrode materials for Li-ion batteries.

Grain storage is an essential part of the food production chain. Therefore, pre- venting grain deterioration is a key issue in a grain storage system. There are several causes for spoilage, all resulting in grain quality and quantity loss. One approach to detect incipient spoilage is by detecting the produced volatiles. In the past, many sensors for detecting volatiles have been developed and are used in industry. However, most of the commercial gas sensors are bulky with high power consumption, mainly limited in range of operating temperature, or require a restricted control over temperature and humidity. This thesis describes the design, fabrication and evaluation of a gas sensor capable of detecting volatiles and considers the potential use of polymer- based sensors. Conductive polymer-based sensors have been reported sensitive to a wide range of volatiles but are commonly evaluated under a controlled environment. Conventional sensor reproducibility and repeatability are also a concern due to the difficulties associated with polymer composite film preparation. In addition, current studies have not fully explored sensor properties in response to humidity, a common factor in any environment, and a variable parameter in grain storage facilities. Moreover, these sensors suffer from ambient temperature dependency as they work based on partitioning mechanism. To enhance sensor performances and eliminate the temperature dependency, a new sensor structure is proposed. The new design uses standard lithography process to fabricate a thermally isolated cantilever containing interdigitated electrodes and a micro-heater to efficiently heat and maintain a constant temperature throughout the interdigitated electrodes. This structure eliminates sensor response drifts caused by ambient temperature variations. Capacitive measurements are performed as the means of volatile detection, which simplify the use of polymers due to the absence of conductive filler and the challenges associated with it. Frequency spectroscopy provides additional information regarding the presence of volatiles compared to conventional resistive sensors, since mechanisms other than swelling are involved. Moreover, frequency and temperature modulations can be employed to further enhance sensor performance, enabling the use of a reduced number of sensors in a sensor array.