Fabrication and evaluation of electrolyte films and high performance electrode materials with metallic catalysts for low-temperature operating SOFC in the next generation

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In this research, the following two projects were carried out for low-temperature operating solid oxide fuel cell which can be operated below or at 800℃ : (1) fabrication of ceramic films of highly oxide ion conducting electrolyte ; (2) preparation of electrode materials with high activities.For the first research project, a new process based on electrophoretic deposition (EPD) was proposed to fabricate electrolyte films supported by porous substrates which can be used as an electrode in the cell. The process enabled us to electrophoretically deposit ceramic powders onto non-conducting porous substrates. Dense yttria-stabilized zirconia (YSZ) films with a thickness of ca. 5μm were successfully fabricated on porous NiO-YSZ substrates by the process proposed. The ~5μm thick dense YSZ films showed maximum output power density of 2.01W/cm^2 at 800℃ with La(Sr)Co(Fe)O_3 cathode. The process was also used to fabricate bilayered YSZ and Sm_2O_3-doped CeO_2 (SDC) electrolyte films. Such bilayered electrolyte films were formed by depositing YSZ followed by SDC without any heat treatment, and then co-fired with substrates. Maximum power densities greater than 0.6 W/cm^2 were obtained at 700 ℃ for the bilayered electrolyte films consisting of ca. 4μm and ca. 1μm-thick SDC films.In the research on electrode materials, (Sr, Ce)MnO_3 perovskite compounds were studied. Although high electrical conductivities were obtained in the compounds, it became apparent that their catalytic properties were not sufficient for application to an electrode in low-temperature operating SOFC.