| Solid oxide fuel cell (SOFC) is an efficient, green energy conversion device. It can convert the fossil energy directly into electrical power without any thermal cycling. SOFC has attraeted wide spread attention due to its high energy conversion efficiency, solid-state structure, clean pollution-free, and awide range of adaptability of fuel gases, etc. The efficiency of SOFC convert chemical energy to electrical energy mainly depends on the electrolyte and electrode performance. The design of cell architecture and electrode microstructure may greatly influence the performance and reliability of SOFC systems. This thesis focuses on fabrieation, improvement and characterization of tubular SOFC. The optimization of electrolyte and electrode are both studied. In the first chapter, this paper introduces the fundamental principles of SOFC, the present researeh status and developing trend. On the base of analyzing the development of SOFC, we fabrieate and investigate a new process forYSZ-based cells for intermediate temperature application (in Chapter 3); developed a cost effeetive and mass produetion proeess to fabrieate YSZ and high temperature proton Conduetor membranes (in Chapter 3 and Chapter 5); effectively improved the nature of the proton conductor material (Chapter 4); particularly, the proton conductors were prepared by sintering of SOFC membrane, the maximum power output performance were achieved at the intermediate temperature of the international literature of (in Chapter 5); and new proton conducting materials have been studied (in Chapter 6). The main achievements and innovations in this paper are summarized as follows:1. We reported our findings in fabrication of anode-supported SOFCs with well controlled microstructures using a simple phase-inversion with dip-coating process. The effect of dip-coating on anode support thickness and the amount of pore former on the porosity and electrical conductivity of the anode supports were systematically studied. Furthermore, anode-supported full cells were fabricated and their electrochemical performances were evaluated under practical fuel cell operating conditions. When the pore former was increased to 6 wt%, the porosity of the anode was increased to～46.9%, while the conductivity was reduced to～578-462 S cm-1 in the temperature range studied. The electrochemical performance was evaluated in a single cell with a configuration of～240μm Ni-YSZ|10μ.m YSZ|20μm LSM-SDC. Peak power density reached 752,646,522,395,277,180 and 277 mW cm-2 at 800, 750,700,650,600,550 and 500℃, respectively, when hydrogen was used as fuel and ambient air as oxidant, which reached to the industry's level of Acumenirics Corporation. The Ohmic resistance (RΩ) was 0.22,0.24,0.27,0.33,0.40,0.84 and 1.76 Qcm2, while the interfacial polarization resistance (Rp) was 0.37,0.51,0.27, 0.70,0.92,1.14 and 3.34Ωm2, respectively, at 800,750,700,650,600,550 and 500℃. The high performance and low resistance of the cells indicate that the tubular SOFC has a good potential for practical applications.2. The BaZr0.1Ce0.7Y0.1Yb0.1O3-δ(BZCYYb) proton conductor materials were prepared by solid-state reaction method, showing very high proton conductivity under 750℃, indicating the application of the high-power output SOFC at low temperature. The particle sizes of ceria and zirconia, sintering times and sintering temperature on the BZCYYb performance have been systematically studied. X-ray diffraction (XRD) show that the micrometer scale and nanoscale cerium oxide zirconia prepared BZCYYb proton conductor material has a typical perovskite structure; Raman spectra show that BZCYYb proton conductor material orthogonal crystal structure; BZCYYb proton conductor pellets were dense by mechanical pressure and sintered at 1500℃for 5 hours; scanning electron microscopy (SEM) show that there is only closed pinhole in the pellets; Archimedes method showed that the density was 96.6%, and shrinkage ratio was 24.0%; four-probe method showed that the BZCYYb proton conductor has a high proton conductivity. In addition, the proton conductivity which measured under different atmosphere has a good linear relationship with the test temperatures. XRD and Raman spectroscopy showed that BZCYYb proton conductor was pure due to complete solid state reaction when sintered at 1100℃for two times; the proton conductivity of BZCYYb which sintered at 1100℃for two times were increased～15% than those which sintered for once. The best sinter temperatue is 1100℃for BZCYYb, the reaction of BaCO3 was not completely at 1000℃; the over sintering phenomena was exist at 1200℃; the proton conductivities of BZCYYb which sintered at 1100℃were increased～30% and～35% than those which the sinter temperature was 1000 and 1200℃.3. We reported a simple and cost-effective process for fabrication of tubular SOFCs with different cathodes, achieving much higher performance than those previously reported. The combination of dip coating and co-firing has produced tubular proton-conducting SOFCs with unique microstructure and superior cell performance. The precursors of tubular cells were with the configuration of～200nm Ni-BZCYYb|～10 nmBZCYYb. The high OCV values indicate that the gas leakage through the electrolyte was negligible and the prepared electrolyte is very dense without any cracks or pinholes. It is expected that optimization of the anode-electrolyte interface microstructure will decrease the anode polarization by increasing the three phase boundaries (TPBs) length. The high performances indicating that the tubular SOFCs based on proton and oxide ion mixed conductor electrolyte have a great potential for practical applications. The impedance spectra and output power density of the tubular SOFC which brushed with pure oxygen ion conductor cathode and oxygen ions proton conductor cathode were similar, demonstrating that the cathode material composition is not the main constraints for oxygen ions and protons transmission. |
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