Electrochemical and kinetic modeling of traditional and mixed-reactant solid oxide fuel cells

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Kenoyer, Kimberly Lynne Christman
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Electronic thesis
Mechanical engineering
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Solid oxide fuel cells (SOFCs) show great promise for commercialization because of the potential for high system efficiency and reduced cost as long as material failures can be addressed and minimized. Mixed-reactant SOFCs (MR-SOFCs) make use of selective catalysts to limit unwanted reactions caused by fuel leaking across cracked electrolyte materials, as well as to simplify SOFC construction to minimize material cracking. It is crucial to understand more about the physics affecting performance of SOFCs in order to compare MR-SOFC technology to traditional SOFCs. In particular, the phenomena resulting from leakage must be categorized to properly analyze the problem and develop solutions.
CO is shown to have an impact on current production in traditional SOFCs. The study also indicated that approximately 9.5% by mole H2 fuel crossover can be tolerated, while CO leakage causes immediate detrimental effects on cell performance. Finally, the MR-SOFC modeled here is shown to be competitive with dual chamber fuel cells experiencing crossover losses, but has significantly decreased performance compared to a comparable ideally functioning SOFC.
A quasi-1D numerical model for the simulation of a traditional (dual chamber) SOFC and mixed-reactant solid oxide fuel cell has been developed based on first principles. The model takes into consideration fuel cell operation at the microscopic level through the use of elementary heterogeneous and electrochemical mechanisms, as well as macroscopic heat transfer considerations. This model is the first to consider elementary kinetic mechanisms at both electrodes and the first to signify the contributions that the individual electrochemical reaction steps have to cell current. The model is also the first MR-SOFC model to consider CO as a fuel for direct electrochemical reaction. The model is comprehensive in that sense that it can be used to analyze many aspects of fuel cell operation and performance, such as: non-equilibrium OCV, species surface coverage, activation polarization, electrochemical reaction rates, and electron production. The model is easily adapted to changing fuel cell materials, properties, fuel types, and to future advances in understanding of heterogeneous and electrochemical kinetics.
August 2013
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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