DEVELOPMENT OF TAPE CAST SOFC ELECTROLYTES AND STUDY THEIR ELECTRICAL AND 4 MECHANICAL PROPERTIES

Abstract

The solid electrolytes, gadolinium doped ceria, Gdo,Ceo9O19s and G42 Ce080j 9c, for application in SOFC were synthesized by nitrate fuel combustion niethod using citric acid as a chelating agent. The synthesized 10-GDC and 20-GDC powders calcined at 700°C. 800°C and 900°C were characterized by X-ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) for phase determination and morphological observation of the powders. Aqueous based tape casting process was adopted to fabricate the solid electrolyte tape of 50-100pm thickness. The precursor slurry of the tape cast was made from the lo-GDC and 20-GDC powders along with several chemical additives viz. polyaerylie acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and octanol dispersed in double distilled water. Several trials were made to optimize the slurry composition. The slurry was ultrasonicated and centrifuged before casting so that complete de-airing is achieved. As east green tapes were dried by convective heating. The tapes prepared with optimum composition of the slurry were of uniform nature and free from cracks. The dried tapes were sintered at higher temperature in several stages. The ealcination temperature of powder and sintering temperature of tape were decided from TG/DT analysis of the dried gel and the green tape respectively. The XRD analysis of the sintered tape sample shows the tape materials have pure Gl)C phase. Further SEM of the sintered tape sample shows the uniform particle shape and size. Particle size was also estimated from the XRD pattern which shows that the size is consistent with the particle size observed by SEM. Increase in the soaking time from 4h to 8h during sintering of tapes resulted in very high densification. Electrical characteristics of the tape samples were observed. Reactance vs. resistance plots over a frequency range of 100 mHz - 1 MHz are presented. The ionic conduetivities of tape samples at room temperature and 500°C are found as 3.33 x 10-10 and 0.01 Scm-I for 10-ODe and 3.19x 10-9 and 0.004 Scm-I for 20-GDC respectively. The activation energies for ion transfer in the samples 10-GDC and20-ODC are 0.74eV and 0.77eV respectively.