Metallic interconnects in intermediate temperature solid oxide fuel cells (IT-SOFC) stacks form Cr2O3 scales on their surface. Such oxide scales can be further oxidized to Cr6+ containing gaseous species that migrate and deposit at the cathode triple phase boundaries, causing significant degradation in the performance of the SOFCs. This phenomenon is termed as ‘Cr-poisoning’. A solution to this problem is the application of coatings on the interconnects that act as a diffusion barrier to Cr migration. Two different Cu/Mn spinel compositions, Cu1.3Mn1.7O4 and CuMn1.8O4, were studied as coating materials. Dense coatings were deposited on both flat plates and meshes by electrophoretic deposition (EPD) followed by subsequent thermo-mechanical or thermal densification steps. At room temperature, Cu1.3Mn1.7O4 coatings were found to have a mixture of CuO and spinel phases, while CuMn1.8O4 coatings were found to have a mixture of Mn3O4 and spinel phases. However, CuMn1.8O4 is a pure spinel phase between 750 °C and 850 °C. After densification processing and high temperature oxidation, a Cr2O3 layer was formed at the coating/alloy interface, which partially reacted with the spinel coatings to form a dense cubic spinel layer of the general composition (Cu,Mn,Cr)3-xO4. In addition, Cr-rich precipitates, formed in the dense layer close to coating/alloy interface. It is believed that these are Cr2O3 precipitates, formed when the solubility of Cr in the spinel phase is reached. Solubility experiments using powders showed that 1 mole of CuMn1.8O4 can effectively getter 1.83 moles of Cr2O3 at 800°C. Electrical conductivity of (Cu,Mn,Cr)3-xO4 was found to be at least two orders of magnitude higher than that of Cr2O3. The coatings acted as an effective Cr getter whose lifetime depends on the oxidation temperature, coating thickness, and the overall porosity in the coating. In-cell electrochemical testing showed that the CuMn1.8O4 coatings on Crofer 22 APU meshes performed significantly better than commercial Cu/Mn spinel coatings. The CuMn1.8O4 coatings gettered Cr effectively for 12 days at 800 ºC, leading to no performance loss of the cell due to Cr-poisoning. Significantly longer lifetime can be achieved at 750 ºC or lower, which is the target operational temperature regime of IT-SOFCs.

A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.

With increasing attention paid to metal-supported SOFCs recently, metal supports have become important factors in the performance of the cells. The formation of surface oxides and the poisoning of Cr from Cr2O3-forming metal supports often result in the degradation of the cells. However, few studies have focused on developing oxidation resistance and decreasing Cr migration from porous alloys in intermediate temperature metal-supported SOFCs. In this work, Y2O3 and CeO2 coatings were applied to porous AISI 430 stainless steels by sol-gel dip coating. Phases and microstructures of the coatings on the porous metal supports were characterized by XRD and SEM with EDS, respectively. The effects of the coatings on oxidation resistance of the supports were evaluated by cyclic oxidation testing. Electrical and electrochemical properties of LSCF-SDC cathodes and symmetrical cells deposited on the Y2O3-protected metal supports were also investigated. The issue of Cr depletion of the supports was also discussed.

With increasing attention paid to metal-supported SOFCs recently, metal supports have become important factors in the performance of the cells. The formation of surface oxides and the poisoning of Cr from Cr2O3-forming metal supports often result in the degradation of the cells. However, few studies have focused on developing oxidation resistance and decreasing Cr migration from porous alloys in intermediate temperature metal-supported SOFCs. In this work, Y2O3 and CeO2 coatings were applied to porous AISI 430 stainless steels by sol-gel dip coating. Phases and microstructures of the coatings on the porous metal supports were characterized by XRD and SEM with EDS, respectively. The effects of the coatings on oxidation resistance of the supports were evaluated by cyclic oxidation testing. Electrical and electrochemical properties of LSCF-SDC cathodes and symmetrical cells deposited on the Y2O3-protected metal supports were also investigated. The issue of Cr depletion of the supports was also discussed.

A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.

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