固体氧化物燃料电池（Solid Oxide Fuel Cell, SOFC）在分布式发电领域具有很好的应用前景。尽管SOFC在近十年来获得了较快的发展，但是其大规模商业化应用仍然受到成本和寿命的制约。目前国内在该领域与国际先进水平还存在较大差距，尤其是在工业尺寸电池、电堆层面。本文针对目前SOFC在能效和寿命方面存在的不足，从能效优化和稳定性解析两个角度开展研究。在能效优化方面：(1) 外部重整（ER-SOFC）是目前最为常见的配置方式，但其发电效率仍有进一步提升的空间。本文首先基于工业用重整器开展了CH4-H2O外部重整多工况测试。随后详细研究了工业尺寸电池在重整合成气下的电化学和输出能效特性。在此基础上，综合考虑电流、燃料流量和电压，提出并比较了三类发电效率优化策略：多工况参数优化、重整合成气除水和阳极尾气梯级利用。最终采用两级电堆结构，实现了50.22%（LHV）的发电效率。(2) 直接内部重整（DIR-SOFC）是未来的发展方向，但是目前其输出性能和稳定性尚存不足。本文分别研究了CH4-H2O、CH4-CO2燃料下气体组分对电池电化学特性的影响。在此基础上，比较了浸渍GDC和添加Ni-GDC催化层两类阳极结构优化策略，发现后者能够有效提高电池在CH4-CO2燃料下的输出性能，运行稳定性也有明显改善。在稳定性解析方面：(1) 尽管目前已经对SOFC性能衰减机理开展了大量研究，但是对各项衰减机理的重要程度缺乏合理的评价和比较。本文首先引入动态电化学阻抗谱（DEIS）测试及分析方法，研究了直流偏置对DEIS及弛豫时间分布（DRT）的影响规律。在此基础上，建立了基于DEIS的SOFC运行稳定性解析方法，能够定量评价不同电极过程对性能衰减的贡献度。(2) 使用该解析方法，分别研究了SOFC在长期运行和运行初期的性能演变机理：i) 对SOFC在1000 h恒电流运行中的性能衰减进行了量化解析和评估。ii) 针对SOFC在运行初期更为显著和复杂的性能演变，首先明确了这一阶段的整体演变规律；随后，重点对初期老化阶段性能快速衰减的现象进行了研究，明确了主导机制是阳极电荷转移反应的劣化。本文有助于厘清CH4等碳氢燃料在阳极侧的转化机理，提出并验证了具有实际可行性的能效优化策略。此外，建立了基于DEIS的运行稳定性定量化解析方法，阐明了SOFC在不同运行阶段的性能演变机制，为进一步提升其寿命奠定基础。
Solid oxide fuel cell (SOFC) can use carbon containing fuels such as methane, coal- or hydrocarbon-derived syngas, and ethanol, which has a promising application prospect in the field of distributed power generation. Although SOFC has achieved rapid development in the past decade, its large-scale commercial application is still restricted by cost and lifetime. At present, in this technical field, there is still a large gap between domestic and foreign advanced technology, especially at the level of industrial size cells and stacks. The energy efficiency and stability of products urgently need to be improved. Aiming at the shortcomings of SOFCs in performance and stability, this study is carried out from the perspectives of energy efficiency optimization and stability analysis.In terms of energy efficiency optimization: (1) External reforming (ER-SOFC) is the most common configuration at present, but the energy efficiency can be further improved. Firstly, an industrial reformer was used to carry out the test of steam CH4 reforming (SMR) under multiple working conditions. Then, the electrochemical characteristics and electrical efficiency of industrial-size cells under reformate fuel were studied in detail. On this basis, considering the effects of electrical current, fuel flow rate and voltage, three optimization strategies were proposed and compared: working parameter optimization, reformate water removal and multi-stage configuration. After comparison, the two-stage stack structure was adopted to achieve 50.22% (LHV) electrical efficiency. (2) Direct internal reforming (DIR-SOFC) is the development trend of SOFC system in the future, however, the output performance and stability of DIR-SOFC are still insufficient. In this study, the effects of fuel composition on the electrochemical characteristics of SOFCs were studied in CH4-H2O and CH4-CO2 atmosphere respectively. In order to further improve the output performance of DIR-SOFC, two anode optimization strategies, i.e. infiltration of GDC and integration of a Ni-GDC catalytic layer, were elaborately evaluated and compared. It was found that the latter strategy can effectively enhance the cell performance under CH4-CO2 atmosphere: the peak power density was increased by 3.3 times, and the stability was also significantly improved. In terms of stability analysis: (1) Although a lot of research has been carried out on the performance degradation mechanisms of SOFCs, at present, there is still a lack of reasonable evaluation and comparison of the importance of different mechanisms. In this study, the measurement and analysis of dynamic electrochemical impedance spectroscopy (DEIS) were first introduced into the field of SOFCs, and the effects of DC bias on DEIS and corresponding distribution of relaxation time (DRT) were studied in detail. On this basis, an analytical method of SOFC operation stability was established, so as to realize the quantitative evaluation of the contributions of different physicochemical processes to the overall performance degradation. (2) Using the established method, the performance evolution patterns of SOFCs during long-term operation and initial-stage operation were studied, respectively. i) The performance degradation of a SOFC during 1000-hour galvanostatic operation was quantitatively analyzed and evaluated. ii) For the more significant and complex performance evolution during initial-stage operation, it was found that the evolution pattern can be divided into activation stage and subsequent aging stage. Afterwards, the phenomenon of rapid performance degradation in the initial aging stage was deeply investigated. It was determined that the dominant degradation mechanism in this stage was the deterioration of anode charge transfer reactions. This study was helpful to clarify the conversion mechanisms of hydrocarbon fuels such as CH4 on the anode side. An energy efficiency optimization strategy with good practical feasibility was proposed and verified. Besides, a quantitative analysis method of operation stability based on DEIS was established and used to clarify the performance evolution mechanisms of SOFCs in different operation stages, which can guide the further improvement of lifetime.
