Preparation Of Solid Oxide Fuel Cells By Phase Inversion And Tape Casting

Solid Oxide Fuel Cell (SOFC) is attracting more and more attention as a direct chemical-to-electrical energy conversion device for its solid-state structure, high efficiency, environmental friendly, etc. Conventional high-temperature SOFC has a strict demand on the materials and fabrication techniques, leading to a high cost on manufacture which limits the practical application of SOFC. Therfore, reducing the SOFC operating temperature is the current research trend.Fabrication of thin electrolyte membrane is one of the most effective techniques to lower the operating temperature of SOFC. In order to develop intermediate-to-low SOFC with lower cost and achieve practicality, this thesis mainly focuses on fabrication techniques for anode supported SOFC and characterization of the electrochemical performances. Moreover, to avoid the drawbacks of cobalt-based cathodes, novel La0.6Ba0.4Fe1-xNixO3-δ cobalt-free perovskite cathodes are also investigated in this thesis.Chapter1reviews the operating principle, critical materials, development tendency and preparation of SOFC. Furthermore, we propose that the thesis aims at the challenge of the cathode materials and fabrication techniques in successful industrialization of SOFC.Chapter2describes the phase inversion method combined with vacuum-assisted coating technique to fabricate the anode-supported tubular SOFC. Phase inversion method was applied to prepare the NiO-YSZ (Yttria-stabilized zirconia) anode support and vacuum assisted coating technique was used to fabricate the YSZ electrolyte membrane. After co-sintered at1400℃, a dense YSZ electrolyte membrane was successfully coated on NiO-YSZ anode substrate pre-sintered at1000℃. With La0.8Sr0.2MnO3-δ-YSZ (LSM-YSZ) as the composite cathode, a maximum power density of155mW/cm2was obtained at700℃for the single cell. Furthermore, the performance was improved significantly by introducing an anode functional layer. Based on the results, the phase inversion method combined with vacuum-assisted coating technique is a simple and efficient process to prepare the anode supported tubular SOFC.In Chapter3, we prepared and studied anode-supported hollow fiber Ce0.8Sm0.2O2-δ(SDC)-based SOFC. The NiO-Ce0.8Sm0.2O2-δ (NiO-SDC) anode hollow fiber was prepared by the phase inversion method and a20-μm-thick SDC electrolyte membrane was deposited on the anode substrate using vacuum-assisted coating technique. With the wet hydrogen (3%H2O) as the fuel, the single cell exhibited the maximum power density of168mW/cm2and the open-circuit voltage (OCV) of0.71V at600℃. Moreover, the OCV was significantly improved by incorporating an electron-blocking layer. Given the high stacking density of the hollow fiber, the hollow fiber SOFC has a high potential for practical applications.In chapter4, planar NiO-BaZr0.1Ce0.7Y0.2O3-δ (NiO-BZCY) anode substrates were prepared by the phase inversion method based on in-situ reaction and the thin BaZr0.8Y0.2O3-δ (BZY) electrolyte membranes with the thickness of25μm were fabricated by a dip-coating method. In order to fabricate suitable substrates, ethanol was introduced into the coagulation bath. The single cell generated maximum power densities of34,55and70mW/cm2at550,600and650℃, respectively, the performance of which is almost an order of magnitude higher than that of the electrolyte-supported SOFC based on BZY electrolyte. It can be concluded that the phase inversion process is also a facile method for fabricating planar SOFC.Chapter5describes a method of tape casting combined with spray coating for preparing the anode-supported proton-conducting SOFC. The NiO-BZCY anode substrates were prepared by tape casting and then pre-sintered at different temperatures. The dense BZCY electrolyte membranes were successfully prepared by a simple suspension spray coating technique. The maximum power density of the single cell achieved97mW/cm2at550℃. In addition, the performance of the single cell (NiO-BaZr0.1Ce0.7Y0.2O3-δ/BaZr0.8Y0.2O3-δ/Sm0.5Sr0.5CoO3-δ-SDC) prepared by spray-tape casting method was also studied. A maximum power density of91mW/cm2was obtained at600℃, which is comparable with the best performance of BZY-based SOFC by far. The results demonstrate the method of tape casting combined with spay coating technique is a low-cost and reliable route to prepare anode-supported proton-conducting SOFC.In Chapter6, perovskite oxides La0.6Ba0.4Fe1-xNixO3-δ (LBFN) were investigated for potential application as Co-free cathodes for intermediate-to-low SOFC. The conductivities increased with increasing Ni content, and the conductivity of La0.6Ba0.4Fe0.8Ni0.2O3-δ (LBFN2) reached300S/cm at450℃. The XRD results revealed that LBFN2and SDC showed excellent compatibility between each other. The AC impedance spectra of the symmetrical cell LBFN2-SDC/SDC/LBFN2-SDC were also investigated and the area specific resistance (ASR) of LBFN2-SDC (7:3in weight ratio) composite cathode was as low as0.17Qcm2at700℃. Using the LBFN2-SDC (7:3in weight ratio) as the composite cathode, the Ni-SDC support single cell with a20-μm-thick SDC membrane exhibited a desirable maximum power density of300mW/cm2at600℃. The results show that LBFN2might be a potential Co-free cathode material for intermediate-to-low SOFC.In chapter7, the researches presented in this dissertation are evaluated and future work concerning the cost-effective preparation techniques of anode supported SOFC is discussed.