8YSZ BASED THIN LAYER SOLID ELECTROLYTE WITH LSGM ADDITION FOR INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELL (SOFC)

• Main Author: Gustaman Syarif, Dani
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/54699
• Institution: Institut Teknologi Bandung

Solid oxide fuel cell is an electrochemical cell that is capable to convert chemical energy to electrical energy directly with low pollution. Currently, operating temperature of the SOFC is relatively high (about 1000 oC), so its operation cost is high. In order to solve that problem, the development of the SOFC is focused on lowering the operating temperature. An effort to achieve that goal is the use of thin solid electrolyte or electrolyte having high ionic conductivity at low temperature. The solid electrolyte of Y2O3 stabilized ZrO2 (YSZ) until now has been the main electrolyte for the SOFC due to its good stability and mechanical properties at high temperature. However, for the SOFC operated at intermediate temperature of 700-800 oC, the ionic conductivity of the YSZ has to be increased and the electrolyte has to be thin. In this research, a fabrication of solid electrolyte based on 8YSZ has been carried out using combination techniques of screen printing and tape casting from local material of zircon in order to get thin layer electrolytes. In order to increase ionic conductivity of the 8YSZ, an addition of LSGM (La1-xSrxGa1-xMgyO3-d) into the 8YSZ was done. Ceramic powder based on the 8YSZ was synthesized by using citric acid as chelating agent from ZrOCl2.8H2O (ZOC) that derived from local zircon using caustic fusion method. The 8YSZ powder was also prepared from commercial ZrCl4 using sol gel method. Powder of LSCF 6428 (LaSrCoFeO3) was prepared by using combination techniques of sol gel and solid state reaction. An anode supported single cell (AS-single cell) was made by a combination technique of screen printing and tape casting. The electrolyte layer was made by screen printing on a smooth surface and on the surface of the electrolyte layer, an anode layer of YSZ-NiO (50:50 weight %) was tape casted. A bilayer of anode-electrolyte was then co-sintered at 1400-1450 oC. The electrolyte side of the bilayer was coated with a paste of LSCF and heated at 1100 oC for 2 hours. Single cell testing was done using hydrogen gas and air, as fuel and oxidant, respectively, at temperature of 700-800 oC. XRD analyses of LSGM-8282 showed that this material crystalizes in perovskite and contains secondary phase of LaSrGa3O7. YSZ crystallizes in cubic with space group of Fm3m and the LSCF crystallizes in rhombohedral with space group of R3c. The addition of the LSGM did not change the crystal structure of the 8YSZ, and the LSGM dissolved in the YSZ. The addition of LSGM increased the grain size, density, and ionic conductivity of the 8YSZ. It was found that the addition of LSGM effectively increased the grain boundary conductivity. The addition of 3 % LSGM increased the ionic conductivity to more than three times of that of the pure 8YSZ, making it possible to be applied for intermediate temperature SOFC. Powder of 8YSZ with controlled impurities has been successfully synthesized from local zircon. The powder had good sinterability. The ionic conductivity of the 8YSZ made of local material at 750 oC was high enough, 21 mS/cm. Hardness and fracture toughness of the 8YSZ from local material also meet the requirement for SOFC application. Microstructure data taken by SEM showed that the electrolyte layer of the 8YSZ from local material having thickness of 10-13 µm could be well fabricated using the screen printing and tape casting methods. ASR (Area Specific Resistance) of these thin electrolyte layers (temperatures of 700, 750, and 800 oC) were 0.093, 0.060, and 0.028 ohm.cm2. The result of the single cell testing showed that the cell fabricated from 8YSZ of local material possessed OCV (Open Circuit Voltage) of 0.96-1.012 V and the OCV of that fabricated from 8YSZ of local materials added with LSGM was slightly smaller, 0.867 V. Maximum power density of the cell fabricated from 8YSZ of local material was 82 mW/cm2 at 750 oC and 102 mW/cm2 at 800 oC. Meanwhile, maximum power density of that fabricated from 8YSZ of local material added with LSGM was 3,5 mW/cm2 at 750 oC. The relatively high value of the ionic conductivity and the OCV of the cell fabricated from local material showed that local zircon could be utilized as base material for production of YSZ based ceramics.