LOW TEMPERATURE CATHODE SUPPORTED ELECTROLYTES

This project has three main goals: Thin Films Studies, Preparation of Graded Porous Substrates and Basic Electrical Characterization and testing of Planar Single Cells. Substantial progress has been made on both characterizing thin films as well as developing methods to produce films on nanoporous substrates. The results of electrical conductivity measurements on ZrO{sub 2}:16%Sc nanocrystalline thin films under controlled oxygen partial pressure and temperature are presented. The experimental data have been interpreted using a defect model, which describes the interaction between Sc and oxygen vacancies resulting in the formation of donor - (Sc{sub Zr} - V{sub o} - e){sup x} and acceptor - (Sc{sub Zr}-h){sup x} levels. From this the electronic and ionic contribution to the electrical transport has been determined and correlated with the band structure. These results suggest that ZrO{sub 2}:16%Sc possesses higher electronic conductivity than ZrO{sub 2}:16%Y, which dominates the total conductivity in reducing atmospheres. This is an important result since it indicates that Sc-YSZ maybe useful in the anode regions of the cell. We have made important breakthroughs on depositing dense Ceria films on to porous LSM substrates. In previous studies we have found that in order to produce a surface which is smooth enough to coat with dense polymer precursor derived films, the required thickness of the colloidal film layer is determined by the maximum surface roughness. That is, if we wish to make 2 micron thick colloidal oxide layers, the roughness of the LSM surface can not exceed 2 microns. Currently, we are producing the composite CeO{sub 2}/LSM structures that can be coated with polymer precursor to produce 0.5 to 1.5 micron thickness dense YSZ films. In the next quarter, we will be testing SOFC's using these structures. YSZ/CeO{sub 2}/LSM composites have been formed by annealing at 800 C. Our studies show that the YSZ films are very dense with a 20 nm grain size. SOFC's using these composites are being fabricated and we expect to obtain cell data during the next quarter. As we reported in November 2000, we have had difficulties in making pore free films with larger areas that about 0.2cm{sup 2} which is due to problems in our clean room. Modifications have now been completed on the clean room and we should be approaching a class 100 in the film making area. This level of cleanliness is sufficient to obtain films without pores over areas up to 100cm{sup 2}