published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

With growing concern for air pollution, global warming, energy sustainability, and oil security, both federal and local governments in the United States have shown greater interest in promoting alternative fuel vehicles (AFVs). Besides attention from the government, consumers in the United States have also shown increasing interest in AFVs, partly due to their concern on the environment and partly due to the increasing gasoline prices. However, despite the raising interest from both the government and the consumers, the number of AFVs in use is still relatively low in the United States. In an effort to promote the adoption of AFVs, the federal and local governments have initiated different incentive programmes for AFVs. Although these “carrots” have been started for more than two decades, studies on the effectiveness of them are still very sparse and are mostly for hybrid vehicles only. Therefore, this study filled in this gap in evaluating the effectiveness of AFV incentives in promoting the ownership and usage of AFVs on a national scale in the United States. As an improvement over prior studies on this topic, this study employed a system of equations approach to capture the interrelationship between households’ vehicle ownership choice and usage, which is often neglected in similar studies. In addition, a Bayesian estimation approach was adopted to overcome the difficulties in the estimation of the system. Using the 2009 National Household Travel Survey data, I found weak relationship between the state level AFV incentives and vehicle ownership and usage. In addition, although I found positive impact of AFV incentives on AFV usage, I also found mixed results on the impacts of the different types of AFV incentives on AFV ownership. These results suggested that further research should be done to investigate why these “carrots” are not as good as expected. / published_or_final_version / Urban Planning and Design / Master / Master of Science in Urban Planning

Solid oxide fuel cells (SOFCs) are power generation devices that offer many great advantages compared to lower temperature fuel cells; for example, they are able to operate at high efficiencies without the use of expensive precious metal catalysts, and are also able to directly utilize hydrocarbon fuels without the need of an external reformer. Unfortunately, the conventional high operating temperature of these devices (T ≈ 1000 °C) requires the use of expensive, specialized materials that can withstand these high temperatures. This issue has generated considerable interest in reducing the operating temperature of these devices to the intermediate-temperature (600 – 800 °C) to allow for the use of less-expensive materials, such as stainless steel. However, the conventionally utilized SOFC cathode materials exhibit poor electrochemical performance at these reduced temperatures. Currently considered alternative intermediate temperature cathodes, such as Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ (BSCF), offer improved performance, but have a large thermal expansion coefficient (TEC), leading to cell failure. In light of these issues, this dissertation focuses on the development of low TEC cathodes for intermediate temperature SOFCS (IT-SOFCs). The primary focus of this dissertation is on the swedenborgite-type RBaCo₃MO₇₊δ (R = Y, In, and Ca; M = Zn and Fe) series of cathodes. Due to their tetrahedrally-coordinated M site, the cobalt ions in these materials do not undergo a spin-state transition, and have TECs similar to conventional SOFC electrolyte materials. The long-term phase stability of these materials was addressed, and it was discovered that a slight In substitution significantly promoted phase stability. In the Y₁₋[subscript x] In [subscript x] BaCo₃ZnO₇₊δ series, it was observed that x = 0.1 successfully stabilized the phase without observable degradation of performance. Similarly, a high-Ca content material (Y₀.₅In₀.₁Ca₀.₄BaCo₃ZnO₇₊δ) was successfully stabilized, though Ca is known to destabilize the phase; furthermore, this compound showed improved performance compared to YBaCo₃ZnO₇₊δ. Lastly, the replacement of the performance-inhibiting Zn with Fe was investigated, and the Y₀.₉In₀.₁BaCo₃Zn₀.₆Fe₀.₄O₇₊δ sample showed low temperature performance rivaling BSCF. Other work in this dissertation focuses on the application of functional silver materials for use in SOFCs, with good performance; these materials were easily manufactured, and they showed performance drastically greater than the conventionally utilized platinum. / text

This dissertation describes the synthesis and characterization of nitrogen doped carbon nanotube (NCNT) supported nanoparticles for catalysis, specifically, the cathodic oxygen reduction reaction (ORR) in fuel cells. Strategies for synthesis of mono- and bimetallic nanoparticle catalysts through dendrimer based templating techniques and with the aid of metal organic chemical vapor deposition (MOCVD) precursors and efficient assembly protocols of the catalysts with the NCNTs are discussed in detail. Physicochemical properties of the NCNTs and NCNT supported catalysts were characterized using a host of tools including scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), thermo gravimetric analysis, BET surface area and pore size analysis and electrochemical techniques including cyclic voltammetry, chronocoulometry, chronoamperometry and rotating disk electrode voltammetry. Chapter 1 serves as a general introduction and provides a brief overview of challenges associated with the synthesis, characterization and utilization of graphitic carbons and graphitic carbon supported catalysts in heterogeneous catalysis. Chapter 2 provides an overview of the synthesis and characterization of systematically doped iron and nickel catalyzed NCNTs in an effort to understand the effect of nitrogen doping on ORR. Chapter 3 describes the use of NCNTs as supports for dendrimer templated nanoparticle catalysts for ORR. A facile synthetic strategy for the immersion based loading of catalysts onto NCNTs by spontaneous adsorption to achieve specific catalyst loadings is explored. Chapter 4 details the loading of monodisperse Pt, Pd and PtPd catalysts on the as synthesized NCNTs using MOCVD precursors. The MOCVD route offers promise for direct dispersion and activation of ORR catalysts on NCNT supports and eliminates a host of problems associated with traditional solvent based catalyst preparation schemes. Chapter 5 details future directions on a few topics of interest including efficient electrodeposition strategies for preparing NCNT supported catalysts, studies on PtCu catalysts for ORR and finally prospects of using NCNT supported catalysts in fuel cell applications.

Reducing fuel consumption and greenhouse gas emissions is becoming increasingly important in the United States, and new legislation can be expected in the near future that will affect trucks either directly or indirectly. This work is a qualitative examination of operational strategies for reducing fuel consumption from freight trucking, and also compares them with vehicular strategies. A focus is placed on who implements, benefits from, and pays for each strategy, and what type of trucking each strategy is applicable to. / text

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