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Solid Oxide Fuel Cells (SOFCs) are considered one of the most promising candidates for future power generation. SOFC operate via oxygen anion transport from the cathode to the anode. This mechanism can allow SOFC to operate on a wide range of fuels, including conventional petroleum, diesel and natural gas and future bio-derived hydrocarbons. In addition, due to the high SOFC operating temperature (>700¼C), SOFC can employ low cost, sulfur and CO tolerant transition metal catalysts. The primary challenge in realizing these direct hydrocarbon SOFCs is the design and development of materials and catalysts for the SOFC anode. These anode materials must be catalytically active for hydrocarbon fuel oxidation while providing sufficient oxygen anion and electronic conductivity to facilitate transport of these species to/from the electrochemical reaction site.

This grant has enabled us to develop techniques for the fabrication and testing of both catalytic materials and SOFC. This work has resulted in three peer-review publications that were partially funded by the ACS/PRF program. The student and faculty salary support provided by this funding has proven invaluable to the research detailed in these papers. Two papers were published during the previous reporting period and full details are described in the 2008 report for this grant. Brief details are supplied in the following. The third paper was published during this reporting period and is described in more detail. Finally, the funds were also partially utilized to support an undergraduate thesis project

The first paper resulting from this funding was a catalytic study of the methane oxidation activity and selectivity of La_0.75Sr_0.25Cr_xMn_1-xO_3-d (LSCM). LSCM is a promising material for the anode of SOFC; however, its catalytic properties have not been examined. We utilized a pulse reactor system to link the catalytic rate and selectivity towards total oxidation of methane to the underlying lattice oxygen non-stoichiometry, d. Both parameters decreased with increasing oxygen non-stoichiometry. In addition, the total activity was strongly influenced by the nature of the B-site cations, with Mn providing higher activity than Cr. It is hypothesized that this is due to more facile reduction/oxidation (redox) of Mn cations within the oxide. This hypothesis is supported by literature reports of a B-site centered catalytic mechanism on this class of materials.

The second publication extended this work towards SOFC manufacture and testing using LSCM as the electrocatalyst. SOFC with LSCM-Cu-yttria stabilized zirconia (YSZ) anodes were tested with H₂, CH₄, and C₄H₁₀ fuel. The performance was significantly higher in H₂ compared to the hydrocarbon fuels, indicating that the activity of the anode towards hydrocarbon fuel oxidation limits cell performance.  The cell resistance was found to significantly with increasing current density through the cell. This was accompanied by a shift in anode selectivity towards total oxidation of the hydrocarbon fuels. This is interpreted based on our previous catalytic study. It is suggested that increasing the current density (and hence oxygen ion flux) to the anode leads to a local decrease in lattice oxygen non-stoichiometry. This is accompanied by a local increase in the rate of oxidation and shift in selectivity towards total oxidation. Both of these contribute to the observed decrease in cell resistance. This initial work funded by the PRF type G award, has been expanded and is continuing under a different funding source.

The third publication supported by this award expanded the project scope towards high temperature proton conducting oxides. This represents a change in operating mechanism for SOFC - from transporting oxygen anions to transporting protons. In order to utilize hydrocarbon fuels with proton conducting electrolytes it is necessary to utilize steam or dry reforming to produce hydrogen. The overall goal of this thrust is to develop high performance anodes that provide high catalytic activity towards both fuel reforming and proton incorporation. One significant issue with this class of materials is that they typically required very high sintering temperatures to form dense ceramics with high ionic conductivity. Our publication examines the use of Co doping to reduce the required sintering temperature by up to 300^oC by introducing up to 10 atom-% Co doping on the B-site of the proton conducting oxide BaCe_0.5Zr_0.4Y_0.1-xCo_xO_3-d (BCZY). The sintering temperature decreased with increasing Co doping. Unfortunately, this was accompanied by a decrease in the stability of the oxide and the emergence of significant electronic conductivity, particularly in reducing gases. An optimum of 3 atom% Co doping has been selected for further study. This expanded work is continuing to study the catalytic properties of these proton conducting oxides and fabricate proton conducting SOFC.

Finally, an undergraduate student completed a senior thesis project with support for materials from this award. Polymer nanosphere were fabricated and self assembled into a close packed structure by controlled drying. This structure was then utilized as a template to form an inverse opal LSCM nanostructure. This was tested as an SOFC anode for hydrocarbon fuel utilization.