Effect of Nickel Addition on Characteristics of Ceria Solid Electrolyte
| Autor: | Li-Jr Liu, 劉力誌 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 To investigate the influences of anode material, nickel, on the structural properties and conduction behavior of the ceria-based electrolyte in solid oxide fuel cell (SOFC) during high operation temperature, nickel element was directly introduced into the yttria-doped ceria (YDC). In the present study, different powder preparation processes were carried out for examining the effects of nickel addition on the properties of YDC electrolyte ceramics. The composite powders, (10YDC)/(NiO) and (20YDC)/(NiO), were respectively prepared using spray pyrolysis (SP) and ball milling (BM) processes. Both the powders were formed by die pressing and sintered at various temperatures for the investigation of the related properties of the composite electrolytes. The experimental data revealed that the particles spray pyrolyzed from cerium nitrate, yttrium acetate and nickel acetate were nanocrystalline and in a hollow spherical structure resulting in lower density of the sintered compacts. The gas-to-particle conversion mechanism caused the bias of the stoichiometry of the resulting powders. The evaluation of lattice constant, analyses of XRD and EPMA suggested that instead of dissolution of the nickel oxide, it tended to segregate on the grain boundaries of the YDC matrices. Furthermore, the impedance and dc resistivity data showed that the conductivity activation energy of the grain increased with the decrease of the sintered density. The effect of grain boundary barrier layer (GBBL) for the nickel oxide segregating on the grain boundary leaded the conductivity activation energy of the grain boundary to increase with increasing the nickel addition reducing the conductivity of the composite ceramics. To improve the sintered density of the electrolyte, commercialized yttria and ceria powders were wet-ball-milled with the addition of nickel acetate to produce the (20YDC)/(NiO) composite powders. After calcining, compacting and sintering, the related properties of the solid electrolytes were further studied. The evaluation of lattice constant, XRD and EPMA analyses revealed that no observable dissolution of the nickel was found in YDC the matrices. Relatively good stoichiometry of each element was gained. The nickel addition improved the sintering densification and conductivity of the YDC electrolyte in BM process. The impedance data showed that the electrode polarization converted the conducting behavior into a mixed ionic-electronic one at the elevated temperature. The dc resistivity results showed that the conductivity increased slightly with increasing the nickel addition; whereas, the conductivity activation energy of grain increased with increasing the grain size showing no influences of the nickel addition. Moreover, the conductivity activation energy of grain boundary increased with the increase of nickel addition suggesting that the effect of nickel introduction tended to occur on the grain boundary in electrolyte matrices during the high operation temperature. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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