| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 95 === To investigate the effects of nickel diffusion on the characteristics and conduction behaviors of the electrolyte in solid oxide fuel cell (SOFC) during high operating temperature, cerium acetate hydrate, yttrium acetate hydrate and nickel acetate tetrahydrate were used as the precursors for preparing the 10 mole% yttria-doped ceria / nickel oxide (10YDC/NiO) ceramic composite powders by spray pyrolysis (SP) in the present study. The resulting powders were then collected by an electrostatic deposition technique (ESD). The results showed the obtained particle size distributed in a specific range depending on the collection voltage and particle size, whereas, revealed to be independent of the composition of the powders. Moreover, the SP particles showed to be hollow in shape with nanocrystalline structures and the surfaces on the particles are revealed to be shrunk and shriveled.
The investigation of focus ion beam (FIB) and high resolution transmission electron microscopy (HRTEM) indicated the formation behavior of the particles to be the surface precipitation mechanism of the precursors. The difference in solubility of the precursors in water leaded the nickel oxide and YDC to precipitate respectively at inner and outer of the particles shell. After die-pressing and sintering, the presence of the pores resulted in poor electric properties of the bulk structure. The synchrotron X-ray absorption spectra for Ni LII, LIII -edge revealed that the nickel had a valence of +2 in the sintered composite. From the results of field emission scanning electron microscope (FESEM) and electron probe micro-analyzer (EPMA), nickel oxide tended to segregate or precipitate along/on the grain boundaries of YDC matrix. The AC impedance data showed that the grain-boundary conductivity of the 10YDC/NiO electrolyte increased with increasing the nickel-oxide content. Such the increasing ratio was proportional to the nickel-oxide content. In the meantime, the activation energy for grain boundary conduction tended to be reduced.
|
|---|
