Dissertation/ Thesis
Processing and Characterization of High Temperature Interfacial Reactions of Electrolytic Ceramics and Electrodes of Planar Solid Oxide Fuel Cells (SOFCs)
| العنوان: | Processing and Characterization of High Temperature Interfacial Reactions of Electrolytic Ceramics and Electrodes of Planar Solid Oxide Fuel Cells (SOFCs) |
|---|---|
| Alternate Title: | 平面型固態氧化物燃料電池之電解質陶瓷與電極之製程與高溫界面反應分析 |
| المؤلفون: | Chih-Chung T. Yang, 楊志忠 |
| Thesis Advisors: | Wen-Cheng J. Wei, 韋文誠 |
| سنة النشر: | 2004 |
| المجموعة: | National Digital Library of Theses and Dissertations in Taiwan |
| الوصف: | 92 In this research, the fabrication and characterization of single solid oxide fuel cell (SOFC), consisting of anode (NiO-YSZ), solid electrolyte (YSZ), and cathode (LSM-YSZ), had been conducted and investigated. The specimens including Ni-YSZ cermets, YSZ, and LSM-YSZ composites were fabricated by tape casting, screen-printing or dry pressing techniques. Besides, an improved anode with gradient composition and porosity was invented by using composite electroplating of Ni with various YSZ aggregates. The specimens were sintered from 1200 to 1600C and then annealed between 800 and 1000C under H2 reducing atmosphere. The phases of the specimens were analyzed by X-ray diffractometer (XRD). The microstructures of the specimens were examined by scanning-, transmission-, and analytical electron microscopes (SEM, TEM and AEM) equipped with energy-dispersive spectroscope (EDS), and high-resolution transmission electron microscope (HRTEM). The electrochemical performances of single SOFC device were measured by using a self-assembled three- electrode apparatus, testing from 500 to 800C under 5 vol% H2 atmosphere with/without H2O humidification. In the investigation of NiO/YSZ, the results showed that the solid solubility of NiO in YSZ should be less than 5 mol% when sintering at 1300C/1 h. The sintered NiO-YSZ or reduced Ni-YSZ cermets showed a uniform two-phase microstructure, consisting of NiO or Ni particles dispersed in the continuous YSZ matrix. When increasing the sintering temperature from 1300C to 1600C, the evaporation of NiO phases took place at high temperature and condensation of NiO occurred during the cooling process. After the reduction, the denser NiO-YSZ cermets resulted in the formation of partially reduced NiO particles and thus the formation of core-shell microstructures, showing the nano-sized Ni crystals and defect clustering of NiO. The size of nano-sized Ni crystals in the shell structure was in the range of 20-30 nm. No inter-diffusion or reaction between Ni/NiO and YSZ was found in the present research after annealing at 1000C for 10 h under 5 vol% H2 atmosphere. In the composite electroplating of Ni-YSZ, the results indicated that no formation of Ni spheres or de-lamination of Ni from YSZ could be found when the Ni-YSZ composites were annealed at 800C for 1 to 10 h under 5 vol% H2 reducing atmosphere. The foldable composite layer showed no de-lamination from Cu or ITO/PET electrode plates after the composite electroplating. The composite layer with gradient composition and porosity can be formed into various 3D electrode structures. In the case of LSM/YSZ interfacial observation, the results showed that the inter-diffusion of cations first caused the amorphization of YSZ, then formed La2Zr2O7 (LZ) or SrZrO3 (SZ) secondary phases if treated for a longer time at 1400oC. The evolution of void-free zone (VFZ), the reaction kinetics of the interfacial reaction, the morphologies of the reaction layer, and the detailed reaction mechanisms were reported. No additional reaction products in LSM/YSZ specimens, sintered at 1400oC and then even treated at 1000oC for 1000 h were detected. In the study of LSM-YSZ composite, the results showed that dense YSZ containing 7.520.15 mol% Y2O3 composed of equiaxed grains. Little glassy phase, consisting of SiO2 with minor Al2O3, was found in YSZ. Two conducting species were responsible for the conduction of YSZ in low and high temperature ranges. One was with higher activation energy of 103 kJ/mol below 550C and the other was with lower activation energy of 93 kJ/mol above 550C. The transition temperature decreased from 550C to 400C for the composites with 10 or 20 vol% LSM-YSZ. The LSM phase and YSZ dominated the electrical conductivity of composites below and above 400C, respectively. As the percolation limit was reached ( 20 vol% LSM), the electrical conductivity of the composites was determined by the LSM phase. The effect of secondary phases on electrical conductivity was insignificant even sintering at 1400C for 24 h. Concerning the electrochemical performance of single SOFC, the results showed that a linear current-voltage (I-V) curve was obtained either for humidified or dry 5 vol% H2-N2 mixture gases at a flow rate of 80 ml/min. The results meant the ohmic polarization was the main polarization loss in the cell. However, the concentration polarization may arise as the flow rate of fuel gas reduces from 80 to 20 ml/min. The power density of single SOFC was 27 mW/cm2 and 23 mW/cm2 for humidified and dry systems when testing at 800C under the 5 vol% H2 at a flow rate of 80 ml/min. |
| Original Identifier: | 092NTU00159009 |
| نوع الوثيقة: | 學位論文 ; thesis |
| وصف الملف: | 175 |
| الاتاحة: | http://ndltd.ncl.edu.tw/handle/03957737980157204080 |
| رقم الانضمام: | edsndl.TW.092NTU00159009 |
| قاعدة البيانات: | Networked Digital Library of Theses & Dissertations |
| الوصف غير متاح. |