Nanoparticulate catalysts infiltrated into SOFC (Solid Oxide FUel Cell) electrodes can significantly enhance the cell performance, but the stability of these electrodes has been an open issue. An infiltration procedure is reported that leads to a stable scandia-stablized zirconia (SSZ) cathode electrode performance.

The effective oxygen conductivities in the zirconia networks of porous LSM-YSZ and LSM-SYSZ composites [i.e. La0.85Sr0.15MnO3 (Y2O3)0.08(ZrO2)0.92 and La0.85Sr0.15MnO3-c2O3)0.1(Y2O3)0.01(ZrO2)0.89, respectively] were evaluated by an AC impedance technique using specimens in which LSM was removed by hydrochloric acid leaching. The oxygen conductivities of porous YSZ and SYSZ alone followed a Koh-Fortini relationship. LSM-containing zirconia network conductivities were additionally decreased by the presence of the LSM, presumably by increased grain boundary resistances. Constriction resistances were estimated to have a minor effect.

An effective, dense and well adherent coating was produced on 430SS that has the result of significantly reducing the oxidation rate of this alloy at elevated temperatures. The coating is essentially a Mn-Co-O spinel, applied in powder form, and compacted to improve its green density. A simplified model is presented that allows an assessment of the effects of the contact and scale geometries. For 850oC, an ASR can be predicted of approximately 0.5 cm2, after 50,000hrs in air, taking into account a factor of 10 penalty for unfavorable contact geometries. The effect of the densified Mn-Co spinel coating is to reduce significantly Cr2O3 sub-scale formation, lower the thermal expansion mismatch, and increase the electronic conductivity of the scale. The findings point to several potential remedies for achieving coatings on 430 SS that allow for metal interconnects with a service life of 50,000hrs or more. Considering contact geometries, such service life is unlikely to be possible above operating temperatures of about 700oC, unless highly specialized alloys are used, with potential processing and cost penalties.

To improve the LSM-YSZ cathode performance of intermediate temperature solid oxide fuel cells (SOFCs), Sm0.6Sr0.4CoO3-sigma (SSC) perovskite nanoparticles are incorporated into the cathodes by a reaction-infiltration process. The SSC particles are ~;20 to 80nm in diameter, and intimately adhere to the pore walls of the preformed LSM-YSZ cathodes. The SSC particles dramatically enhance single-cell performance with a 97 percentH2+3 percentH2O fuel, between 600oC and 800oC. Consideration of a simplified TPB (triple phase boundary) reaction geometry indicates that the enhancement may be attributed to the high electrocatalytic activity of SSC for electrochemical reduction of oxygen in a region that can be located a small distance away from the strict triple phase boundaries. The implication of this work for developing high-performance electrodes is also d iscussed.

The fabrication and electrochemical performance of co-fired, LSM-SYSZ [i.e., La0.65Sr0.30MnO3 (LSM) - (Sc2O3)0.1(Y2O3)0.01(ZrO2)0.89] supported thin-film cells were examined using humidified hydrogen as a fuel. Co-firing of bi-layers and tri-layers was successful at 1250oC by optimizing the amount of carbon pore formers. A power density of a factor of 2.5 higher than that recently reported for the same type of cell at 800oC [3] was obtained for a cell with cobalt infiltration into the supporting cathode: the peak power densities were 455, 389, 285, 202, 141 mW/cm2 at 800, 750, 700, 650, 600oC, respectively, and in most cases power densities at 0.7V exceeded more than 90 percent of the peak output. Increasing the cathode porosity from 43 to 53 percent improved peak power densities by as much as 1.3, shifting the diffusion limitation to high current densities. Cobalt infiltration into the support improved those by as much as a factor of 2 due to a significant reduction in non-ohmic resistance. These results demonstrate that cobalt catalyst-infiltrated LSM can be effective and low-cost supporting electrodes for reduced temperature, thin film SOFCs.

Solid oxide fuel cell (SOFC) membranes were developed in which zirconia-based electrolyte thin films were supported by a composite metal/ceramic electrode, and were subjected to rapid thermal cycling between 200 and 800 0C. The effects of this cycling on membrane performance were evaluated. The membranes, not yet optimized for performance, showed a peak power density of 350mW/cm2 at 900 0C in laboratory-sized SOFCs that was not affected by the thermal cycling. This resistance to cycling degradation is attributed to the close matching of thermal expansion coefficient of the cermet support electrode with that of the zirconia electrolyte.