Dissertation Defense – Brian Doyle
Dr. Meilin Liu, Advisor, MSE
Dr. Faisal Alamgir, MSE
Dr. Mark Losego, MSE
Dr. Matt McDowell, MSE/ME
Dr. Larry Bottomley, CHEM
"Rationale Design of Surface Modification for Solid Oxide Fuel Cell Electrodes"
The modern world is defined by the insatiable demand for energy as standards of living increase throughout the world. The Energy Information Administration projects that global energy consumption will increase by 48% to 815 quadrillion BTU by 2040 driven in major part by growth in developing countries. Meeting that demand requires technological advancements that accommodate a range of national priorities including economic and environmental constraints. Solid oxide fuel cells (SOFCs) represent an attractive technology to meet these demands. SOFCs operate through the electrochemical oxidation of a fuel gas and thus are not constrained by the Carnot efficiencies of combustion engines. That allows SOFC systems to attain electrical efficiencies on the order of 80%. In addition to higher efficiencies, SOFCs are scalable and fuel flexible without requiring expensive metal catalysts. However, there are several constraints that limit the wide-spread commercialization of SOFCs. While high temperature operation (800-1000°C) allows for non-precious metal catalysts, the complex oxides degrade before the system becomes economically viable. Lowering the operating temperature can mitigate the degradation behavior in both the active material and system level components. Unfortunately, as temperature decreases, the resistances for the electrochemical reactions increase. The intermediate temperature range of 500-800°C has been identified as a compromise between decreasing reaction rates and increasing material durability. Thus, it is important to engineer materials to enhance catalytic activity at these intermediate temperatures. The purpose of this dissertation is to explore routes to increase performance of the SOFC electrodes through surface modification at these intermediate operating temperatures and identify principles that will guide rational design of the next generation of SOFC electrodes.
This work focuses on the modification of state-of-the-art cathodes with different conformal and patterned thin films. A variety of conformal and non-conformal thin films deposited via infiltration, physical vapor deposition and atomic layer deposition have shown performance enhancement and reduced degradation rate, but a full set of guiding principles has not been established. The first part of this dissertation focuses on the development of a thin film asymmetric cell testing platform that can be used to better understand the effect of thin films on the surface of the cathode. The La0.6Sr0.4Co0.2Fe0.8O3-δ cathode backbone is a mixed electronic and ionic conductivity that is deposited via RF sputtering. The asymmetric cell configuration is fully characterized as a platform for further testing. The second part of this dissertation describes surface modification of ceria and doped ceria using this new platform to unravel the enhancement mechanism with different patterned features. The third part of this work uses the praseodymium-doped ceria system to better understand the role of electronic and ionic defects in performance enhancement. In the end, rational design guidelines are developed to guide future surface modification of solid oxide fuel cell electrodes.