Title

Computational Modeling and Experimental Examination of Microstructure and Oxidant Source on Solid Oxide Fuel Cell Electrodes

Date of Completion

January 2011

Keywords

Engineering, Chemical|Engineering, Mechanical

Degree

Ph.D.

Abstract

This dissertation examines the complex microstructures of solid oxide fuel cell (SOFC) electrodes along with the transport phenomena and chemical reactions that occur within to realize increased performance and durability of SOFC systems. X-ray nanotomography is performed on the anode to obtain three-dimensional (3-D) volumes of the microstructure at the pore level. These volumes are analyzed to determine structural parameters of the anode and are used in a tubular SOFC model to predict polarization curves. The model is integrated with an auto-thermal reformer (ATR) to predict the performance of SOFC systems using pre-reformed CH4 fuel. The integrated SOFC model can be used as a design tool to engineer better electrodes and optimize the system. Performance and durability of the cathode is considered for an air independent SOFC system using a decomposed H2O2 oxidant stream. A fully decomposed 50% H2O2 stream contains 83% H2O(g), a value much higher than typically observed under normal operating conditions. The role of high H2O(g) on cathode stability, transport phenomena, cell performance and oxygen reduction kinetics is not well understood and is addressed in this dissertation. Stability is studied with H2O(g) exposure experiments. Modeling of the mass and charge transport in the cathode with detailed reaction kinetics is performed to understand the transport processes under high H2O(g) content. Electrochemical Impedance Spectroscopy (EIS) and Tafel measurements are performed on symmetric cathode cells to investigate the cell performance and reaction kinetics with high H2O(g) in the cathode oxidant stream. Understanding the cathode processes provides better performing cathodes and optimization for SOFC operation on H2O2 oxidant. This work provides an improved understanding of the anode microstructure, the role of high H2O(g) in the oxidant stream and modeling tools to design anodes and cathodes with improved performance. ^