The Use of Cerium Oxide as an Anode Catalyst in Solid Oxide Fuel Cells

Steven C. DeCaluwe, University of Maryland

Solid Oxide Fuel Cells (SOFCs) are an important electrochemical power conversion device, due largely to their high efficiencies and ability to directly oxidize a variety of fuels, including hydrogen, carbon monoxide, and light hydrocarbons (HCs). While nickel is the most common SOFC anode catalyst, Ni-based SOFC anodes are prone to failure from a variety of sources. For this reason, ceria (CeO2) is being explored to replace or supplement Ni in SOFC anodes. CeO2, a mixed ionic-electronic conductor (MIEC), has been shown to improve SOFC anodes. resistance to carbon deposition and sulfur poisoning. However, optimization of such systems has proven difficult due to a range of issues, related both to the broader understanding of SOFC processes and the unknown role of ceria during SOFC operation. While studies have demonstrated the ability of quantitative physical models to describe the electrochemical behavior of simplified SOFC geometries, there has been less success describing the coupling between electrochemistry and mass transport in more relevant, complex SOFC geometries. Furthermore, the electrochemical mechanisms and reaction rates needed to describe fuel oxidation on ceria anodes are not well understood. Complicating matters is the MIEC nature of ceria. Both Ce4+ and Ce3+ are present during fuel cell operation, and the ionic and electronic conductivities are determined by the abundance of Ce3+. The in-situ spatial distribution of valence states, then, is expected to have a major impact on ceria.s role in SOFC anodes. A range of experimental and numerical investigations have been undertaken at the University of Maryland to both understand the fundamental role of ceria in SOFC anodes, as well as integrate this knowledge into working SOFC models that can be used to predict and optimize performance. The author will present an overview of his research efforts undertaken at UMD.including button-cell experiments on idealized ceria anode geometries, characterization of ceria valence states via in-situ XPS measurements, and numerical simulations of traditional (porous-media) and idealized (thin-film) SOFC architectures.and will discuss the lessons learned regarding SOFC performance and the role of ceria in SOFC anodes.

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