【作者】 付长璟；

【导师】 孙克宁；

【作者基本信息】 哈尔滨工业大学 ， 应用化学， 2007， 博士

【摘要】 固体氧化物燃料电池（SOFC）具有能源转换效率高、对环境污染小等优点,被誉为21世纪的绿色能源。近年来,随着新型的电极和电解质材料的不断开发,阳极支撑型平板式SOFC的出现,SOFC的工作温度逐渐降低,使得采用廉价的合金材料作为其连接体材料成为可能。但在SOFC高的工作温度下,合金材料作为其连接体材料在合材料和结构设计等方面还存在着一系列问题。本论文工作主要是通过开展合金连接体材料和结构方面的系统研究,深入地理解了合金连接体的工作特性,为今后组装SOFC电堆打下了坚实的基础。研究了SUS430合金作为SOFC连接体材料的基础性能,以La0.8Sr0.2MnO3-δ（LSM20）阴极为例,深入地研究了SUS430合金中Cr对阴极的毒化作用机理,明确了Cr对阴极毒化程度的决定因素。结果表明,SUS430合金的热膨胀系数（TEC）与其它电池组件,尤其是阳极基体非常接近;在SOFC工作条件下,尽管合金的氧化增重速率较慢,但其面电阻增长较快,超出了SOFC对连接体的阻值要求。Cr对LSM20阴极的毒化作用主要是抑制电极表面氧还原反应（ORR）过程,在阴极极化初期,气态铬的氧化物抑制了氧在LSM20电极表面的解离吸附和气体扩散过程;随着极化时间的延长,固态铬的氧化物,如Cr2O3/（Cr,Mn）3O4相的逐渐生成,增大了氧离子迁移和扩散阻抗。Cr对阴极的毒化程度受阴极的工作气氛、电极结构和材料的影响,可以通过降低阴极工作气氛中的氧气和水蒸气分压,选择具有更多氧空位的阴极材料以及合理地优化阴极结构得以改善和抑制。SUS430合金与Ni-YSZ阳极具有良好的化学相容性。提出了以改进的等离子喷涂方法制备的La0.8Sr0.2FeO3-δ（LSF20）作为合金连接体阴极侧保护层,以金属Ni作为阳极侧保护层。通过对多种陶瓷材料的电导率和TEC的比较和分析,选择了LSM20和LSF20作为合金连接体的阴极侧保护层材料,采用大气等离子喷涂方法制备了合金连接体阴极侧保护涂层,并适应SOFC工作环境特点,改进了等离子喷涂的后封孔工艺,提出了以LSM20和LSF20的硝酸盐溶液浸渍、原位烧结的方法对等离子喷涂涂层进行后封孔处理,取得了较好效果,涂层显气孔率低于1%。性能测试结果表明,LSF20涂层在抗高温氧化、抑制合金中Cr的挥发和扩散等方面都明显优于LSM20涂层,其在800℃空气中氧化1000h,面电阻仅为1mΩ·cm²,比目前国际上报道的合金连接体阴极侧保护涂层面电阻的最低值（2mΩ·cm²）低1倍。连接体阳极侧分别采用等离子喷涂方法和电化学沉积方法制备了金属Ni保护层,等离子喷涂Ni层与合金连接体具有更好的结合强度,在SOFC阳极工作气氛下的面电阻较低。设计了连接体与电极之间的汇流结构。通过电极的极化曲线、电化学阻抗和面电阻等方面的测试与分析,明确了汇流层的作用和结构要求,电极接触层不仅可以降低电池的欧姆电阻,而且能够有效地提高电极表面ORR催化活性;电极支撑层只在电极和连接体之间起传导电子的作用,不影响电极表面ORR过程。本文提出了以固相反应法制备的La_0.6Sr_0.4CoO_3-δ（LSC）和Ag浆作为阴极接触层,以粒径为0.68μm的NiO和Ag浆作为阳极接触层,并通过在接触层表面用嵌入银浆的银丝固定支撑层来实现支撑层与接触层的良好电连接,连接体与电极之间的接触电阻降低了50%以上,接近目前国际报道最好水平。建立了SOFC有限体积量化分析模型。该模型基于电化学反应动力学理论,并结合现象学原理,采用“比例因子”的思想,将结构参数的优化转化为比例因子的选取问题。比例因子以小步长改变,通过计算电池极化过电势的数值大小,实现连接体的结构参数优化,为连接体的结构设计提供了量化的理论指导。模型还分析了燃料电池的工作条件对其性能的影响。设计了一套电池连接体板,连接体阴、阳极侧表面分别等离子喷涂了LSF20和金属Ni保护层,采用优化的汇流结构,组装电池,测试结果表明,放电性能与数值计算结果基本吻合。更多还原

【Abstract】 Solid Oxide Fuel Cell (SOFC) has been considered as one of major green energy in the 21st century because SOFC has ultra-high energy conversion efficiency and ultra-low pollutant emission. Over the past few years, research and development of both new electrodes and electrolytes and the advent of the anode-supported planar SOFC design have led to a steady reduction in the SOFC operating temperature. Consequently, it becomes more realistic now to use low cost heat-resistant alloys for interconnect components in the SOFC stack. However, there are some serous problems for using alloys as interconnect materials at the high operating temperature of SOFC including the materials and the structure design. The main work of this thesis focuses on the systematic study on the alloy materials and the structure of interconnects in order to make an intensive comprehension on the properties of alloy interconnects and lay the foundation for the fabrication of the SOFC stack.This thesis has evaluated the fundamental properties of SUS430 alloys as SOFC interconnect materials. Taking the LSM20 cathode as an example, the mechanism of chromium poisoning to the cathode was studied in details; and the determinants of the poisoning degree of chromium to the different cathodes were clarified. The compatibility of SUS430 alloy with the Ni-YSZ anode was also studied. Results showed that the thermal expansion coefficient (TEC) of the SUS430 alloy was very close to that of the electrodes under the SOFC operating atmosphere, especially the anode substrate. Although the oxidation growth rate of the alloy was relatively low, the increase of area specific resistance (ASR) was much higher than the acceptable level for SOFC interconnects. The poisoning of chromium to the LSM20 cathode would inhibit the oxygen reduction reaction (ORR) on the surface of LSM20 cathode. At the initial stage of polarization, the dissociative adsorption and the diffusion of oxygen on the LSM20 electrode surface were inhibited by the gaseous Cr species. With the time prolonging, the migration processes of oxygen ions into YSZ electrolyte were inhibited by the solid Cr species, such as Cr2O3 and (Cr,Mn)3O4, deposited on the electrolyte surface. The degree of chromium poisoning to the cathode was determined by the cathode atmosphere, the electrode structure and the cathode materials. Therefore, it is reasonable to inhibit the chromium poisoning to the cathode by lowering the partial pressure of the oxygen and vapor in the cathode atmosphere, selecting the cathode materials with more oxygen vacancies and rationally optimizing the cathode structures. SUS430 alloy was compatible with the Ni-YSZ anode.La0.8Sr0.2FeO3-δ(LSF20) was proposed as the interconnect protective coatings in the cathode side and the metallic nickel was proposed as the interconnect protective coatings in the anode side by the improved APS method. Many kinds of ceramic materials were investigated on their conductivity and TEC, LSM20 and LSF20 were finally selected as the protective coating materials for the interconnects made of SUS430 alloys in this thesis. The protective coating in the interconnect cathode side was prepared by the APS method. The densification technique of APS was improved to adapt to the SOFC high operating temperature. A method of nitrate solution impregnation and sintering in situ was proposed to realize the further densification of the as-prepared APS coating. As a result, this made a perfect effect and the open porosity was below 1%. The properties of the LSM20 and LSF20 coating were compared. Results showed that LSF20 coating could more effectively reduce the high temperature oxidation rate of SUS430 alloys and inhibit chromium evaporation and diffusion through the coating. The ASR of the LSF20 coated SUS430 alloy was only 1m??cm2 after being oxidized in air at 800℃for 1000h, which is only half of the lowest ASR value (2m??cm2) of the interconnects cathode protective coating after the same treatment according to the recent international reports. A metallic nickel coating was prepared by the APS and the electrochemical deposition method, respectively. The nickel coating prepared by the APS method adhered more tightly to the alloy substrate. Therefore, a lower ASR was obtained by SUS430 alloys with the APS nickel coating under the SOFC anodic atmosphere. The current collecting structure was designed in this thesis. The current collector’s function and its structural requirements were confirmed by analyzing the results of the electrochemical polarization curves test, electrochemical impedance test and ASR test. Results showed that the electrode contactor can not only reduce the ohmic resistance of the fuel cell, but also improve the catalytic activity of the ORR on the electrode surface. The electrode supporter only played a role in electrical conductivity and did not influence the ORR catalytic activity of the electrodes. A noble contactor of La0.6Sr0.4CoO3-δ(LSC) prepared by solid state reaction method and silver paste was proposed as the cathode contactor. The anode contactor proposed in this thesis was composed of NiO (particles diameter: 0.68μm) and silver paste. A reduction greater than 50% was obtained for the contact resistance between the interconnect and the electrode by fastening the supporters with the silver lead embedded in the silver paste on the contactor surface, and the result was close to the best result presently known.A finite volume quantification analysis model was constructed based on the theory of electrochemical reaction kinetics combined with phenomenology. The idea“ratio factor”was adopted to convert the structural parameters optimization into the selection of the ratio factors. Optimization of the interconnect structural parameters was realized by calculating the simulated unit cells polarization with the changes of the ratio factors in a small step. At the same time, it provided a qualification and theory guidance for the SOFC interconnect structural design. The effects of SOFC operating conditions on the fuel cell performance were also evaluated in this thesis. A set of interconnects were designed and sprayed with the LSF20 protective coating in the cathode side and metallic nickel protective coating in the anode side by the APS method, respectively. The optimized current collectors were applied in the fabrication of the fuel cells. Discharging results were close to those of the simulation.更多还原