SOLID OXIDE FUEL CELL MATERIALS SYNTHESIS FROM AQUEOUS SOLUTIONS. Takeshi Yao, Akira Ariyoshi and Takashi Inui, Faculty of Engineering, Kyoto University, Kyoto 606 Japan
Novel methods for synthesizing ZrO2 crystals and LaMeO3 (Me=Cr, Mn, Fe, Co) perovskite crystals from aqueous solutions at ordinary temperature and pressure were discovered. These methods are expected to be applied to film preparations. ZrO2 and LaMeO3 perovskites now are paid great attentions as the electrolyte, the cathode or the interconnection materials for solid oxide fuel cells (SOFC). The thin film shapes are desirable, however, the usual manufacturing methods such as CVD, sputtering, sol-gel, etc. have some disadvantages. Methods for forming films from aqueous solutions are advantageous because of lower cost, requirement of no vacuum or no high temperature and applicability to films with wide areas and/or complicated shapes.
1. ZrO2 crystals synthesis
Boric acid was added into the sodium hexafluorozirconate solution, the fluoride ion was consumed by the formation of BF4-, then the hexafluorozirconate ion was hydrolyzed to ZrO2 in order to increase the amount of the fluoride ion. The X-ray diffraction peaks were strong and sharp enough to confirm the high crystallinity. In SEM photograph, there observed particles gathering, growing connecting and uniting each other to form a film like aggregates.
2. LaMeO3 perovskite crystals synthesis
The valence state control of the transition metal ions was important and a sophisticated technique was contrived. Powder of LaMeO3 perovskite produced by the usual solid state reaction was dissolved in hydrofluoric acid solution which is expected to neither oxidize nor reduce the transition metal ions, then the solution of metal fluoride having the same valence states as those in the perovskite crystal was obtained. Boric acid was added into the solution, then LaMeO3 perovskite crystal was formed by the similar mechanism as that of the ZrO2 synthesis. The high crystallinity was indicated by the strong and sharp X-ray diffraction peaks. In the SEM photographs, there observed highly dispersed particles about 1~5 um on the substrates.