Development and Characterization of the Electrolyte Supported Micro Tubular Solid Oxide Fuel Cells

• Main Authors: Hsieh, Wen-Shuo, 謝文碩
• Other Authors: Lin, Pang
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/99602050053119767747

博士 === 國立交通大學 === 材料科學與工程學系所 === 102 === In this study, dense electrolyte supported micro tubular solid oxide fuel cells (T-SOFCs) were prepared by extrusion and dip-coating. Green Zr0.8Sc0.2O2−δ (ScSZ) electrolyte micro-tubes with a thickness of 300 m were successfully prepared at room temperature. After firing at 1400oC, the bare electrolyte micro-tube with a thickness of 210 μm, a diameter of 3.8 mm, and a length of 40 mm reached a relative density of 96.84% and a flexural strength of 190 MPa. Furthermore, the effects of the GDC-LSCF (Ce0.8Gd0.2O0-δ-La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode layer and the GDC interlayer on the electrochemical performance of the ScSZ (Zr0.8Sc0.2O2−δ) electrolyte supported (270 μm) micro-tubular SOFC cells are investigated. Material formulation and sintering profile for fabricating the micro-tubular SOFC cells are developed to avoid physical defects caused by the large sintering shrinkage mismatch among the layers. Cell B (with the LSCF-GDC composite cathode layer and the GDC interlayer) reports an ohmic resistance slightly higher than that of Cell A (with the GDC-La0.8Sr0.2MnO3-δ, i.e. LSM, composite cathode), while its polarization resistance emerges to be significantly smaller than that of Cell A. In terms of cell performance, Cell B demonstrates an OCV value (> 1.07 V) similar to that of Cell A and a maximum power density (MPD = 0.26 Wcm-2) 44.4% greater than that of Cell A (MPD = 0.17 Wcm-2) at 850oC. It can thus be concluded that using the LSCF-GDC composite-cathode layer and inserting the GDC interlayer help reduce the total cell impedance, thereby improving the power density of the tubular cells. On the other hand, a gadolinia-doped ceria (GDC)-supported micro tubular SOFC was fabricated using extrusion and dip-coating (Cell C). The effects of inserting a scandium-stabilized zirconia (ScSZ) layer as an electron blocking layer between the GDC layer and the GDC-NiO anode layer were also explored (Cell D). The microstructures and electrochemical performances of Cell C and Cell D were investigated and compared. The layer thicknesses of the GDC and ScSZ bi-layer electrolytes were approximately 285 μm and 8 m, respectively. With the inserted ScSZ layer, the ohmic resistance increased by 49.3%, 31.4%, 19.0%, and 17.1%, and the polarization resistance rose by 220.6%, 321.4%, 540.0%, and 566.7% respectively, at the temperatures of 650, 700, 750, and 800oC. The increase in the ohmic resistance of Cell D was predominantly due to the interfacial resistance, while the substantial escalation in the polarization resistance was mainly because of the low bulk oxygen diffusion process in the ScSZ layer and the smaller charge transfer processes occurring at the interfaces. The OCV of Cell D showed a slight decrease from 1.06 to 0.98 V and that of Cell C experienced a dramatic decline from 0.92 to 0.76 V as the temperature rose from 650 to 800oC. The ScSZ layer of Cell D had successfully inhibited the OCV loss caused by the electronic conduction in GDC. The maximum power densities of Cell C and Cell D were measured to be 0.20, 0.27, 0.33, and 0.36 Wcm-2, and 0.16, 0.23, 0.32, and 0.42 Wcm-2 at 650, 700, 750, and 800oC, respectively. The MPD of Cell D was improved at temperatures above 750oC but remained inferior to that of Cell C below 750C. This is due to the fact that, as operating temperature increased above 750oC, the benefit of the higher OCV in Cell D surpassed the deficiency of the higher cell resistance, thereby leading to a higher MPD.