【作者】 黄秋安；

【导师】 汪秉文；

【作者基本信息】 华中科技大学 ， 控制理论与控制工程， 2009， 博士

【摘要】 在车辆和舰艇等移动应用领域，金属支撑固体氧化物燃料电池SOFC具有很高的应用潜力。然而，为实现大规模商业化应用，金属支撑SOFC技术在高成本和低可靠性上必须取得实质性突破。在面对上述挑战的持续努力中，电池性能优化测试和失败模式诊断发挥着重要作用。在燃料电池诊断工具中，交流阻抗谱，也称为电化学阻抗谱，被广泛用来作为电池性能评价和退化诊断分析。本文主要采用交流阻抗谱及其模型诊断方法，并结合电压-电流-功率密度极化曲线、扫描电子显微镜技术、能量分散X射线技术、X射线衍射技术以及热循环分析方法，研究金属支撑SOFC极化特性，诊断电池退化机理，以及评价电池动态特性。由脉冲激光沉积和悬浮等离子喷涂工艺制作的试验样品SS430／NiO-SDC／ScSz／SDC／SSCo-SDC和Hastelloy X／NiO-SDC／SDC／SSCo-SDC是本文研究对象，讨论主要集中在电池结构、关键材料、制造流程以及在本工作中所采用的表征方法。本文也对燃料电池的交流阻抗谱诊断的本质进行了讨论，并首次从模式识别和系统诊断的视角给出阻抗谱诊断的理论架构，该架构主要由六个状态和五个动作构成。另外，本文还系统全面地比较分析了不同阻抗谱模型在SOFC领域中诊断特点。基于SOFC交流阻抗谱等价电路模型，本文深入研究了两金属支撑SOFC单体电池的极化特性。在400～600℃温度范围，从电化学角度比较和分析SDC单电解质层和双电解质层SSCo／SDC结构金属支撑SOFC，它们分别为脉冲激光沉积和悬浮等离子喷涂工艺制作，在比较和分析时，重点关注阴极交换电流密度、极化损失以及最大功率密度。试验和仿真结果说明，运行温度和制造工艺在金属支撑SOFC线性极化特性中扮演重要角色。因此，为了降低电池极化损失，必须优化沉积工艺对界面形貌的影响。为了诊断Hastelloy X／NiO-SDC／SDC／SSCo-SDC金属支撑SOFC退化机理，本文提出一个混合电子离子导体等价电路模型。在金属支撑SOFC领域，本文提出的等价电路模型首次将退化诊断分析所必须的参数有效关联，而且，该模型具有良好的数学可解析性。该等价电路模型的诊断结果表明，在450～600℃温度范围，高接触电阻是阻碍金属支撑SOFC性能的关键因素。试验观测到的金属支撑体／阳极界面氧化物薄膜以及电解质／阴极界面弱的结合力可能对高的接触电阻负责，此观测结果也验证了本文提出等价电路模型的有效性。另外，借助提出的等价电路模型，定量评价了金属支撑SOFC内部电子传导。同时，为了评价金属支撑SOFC动态性能，本文进行了热循环测试实验。在15次热循环测试期间，电池开路电压维持相对恒定，然而，交流阻抗谱结果显示，电池性能退化相当明显。相对恒定的开路电压显示，电解质层经受住了热冲击，此受益于金属支撑体良好的导热性和延展性。实验观测到的电池性能退化现象很可能归咎于电解质材料与阴极材料热膨胀系数不匹配以及金属支撑体的氧化，此结论同由等价电路模型推导出的电池退化机理相吻合，也再次验证了本文提出等价电路模型诊断结果的有效性。综上所述，本文为SOFC阻抗谱诊断提供了完整的理论架构和切实可行的诊断方法，而且，本文的诊断结果，可为金属支撑SOFC性能优化和稳定性改进提供先决条件和理论基础，从而加速金属支撑SOFC商业化进程。更多还原

【Abstract】 Metal-supported solid oxide fuel cells (SOFCs) are recognized to have a high potential for use in mobile application, such as vehicle and naval vessel. However, in order to make a breakthrough in metal-supported SOFC technologies, two major challenges, high cost and low reliability, have to be overcome in the path towards commercialization. In the continuing effort to address these challenges, fuel cell testing for performance optimization and failure mode diagnosis is the necessary step. Among the major fuel cell diagnostic tools, AC impedance, also called electrochmical impedance spectroscopy (EIS), has been widely used for performance evaluation and degradation diagnosis. At present work, AC impedance and its model-based diagnosis method, combined with current-voltage-power curve, energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), X-ray Diffractometer (XRD), and fast thermal cycle techniques, was applied to investigate polarization characteristics, to diagonize the degradation mechanism, and to evaluate the dynamic properties of metal-supported SOFCs with SDC as electrolyte. These research contents are summarized as follows:The studying objects SS430/ NiO-SDC/ScSz/SDC/SSCo-SDC and Hastelloy X/NiO-SDC/SDC/SSCo-SDC, fabricated by pluse laser deposition and suspension plasm spray respectively, were detailedly stated firstly. The discussions concentrate on cell structure, key materials, fabrication procedures, and characterization methods adopted at present work. The nature of AC impedance diagnosis was addressed as well. In fuel cell field, the complete theoretical framework for AC impedance diagnosis was firstly presented from the viewpoint of pattern recognition and system diagnosis, and the framework mainly consists of six states and five actions. In addition, SOFC impedance models were analyzed and compared completely and systematically in terms of the application properties.Based on AC impedance equivalent circuit model for SOFC, polarization characteristics of metal-supported SOFCs were investigated in deep. The two metal-supported SOFC cells with single-layer electrolyte of SDC and double-layer electrolyte of SDC-ScSz, fabricated by suspension plasma spray and pulse laser deposition respectively, were compared and analyzed from the viewpoint of electrochemistry, focusing on cathode exchange current density, polarization loss, and maximum power density over the temperature range of 400～600℃. Results from experiments and simulation indicate that fabrication processes and operation temperatures play an important role in the electrochemical mechanism for the linear polarization characteristics of metal-supported SOFCs. Consequently, it is necessary to optimize the deposition processes related to interfacial morphology in order to reduce the cell polarization loss.In order to diagnosize the degradation mechanism of the metal-supported SOFC, consisted of Hastelloy X/NiO-SDC/SDC/SSCo-SDC, an equivalent circuit model considering mixed ionic-electronic conducters was presented in present work. In metal-supported SOFC field, the presented equivalent circuit model firstly correlates the necessary parameters for the degradation diagnosis; moreover the model exhibits mathematical tractability. The diagnosis results based on the presented equivalent circuit model indicate that the high contact resistance is a prominent factor impeding the performance of metal-supported SOFCs at 450～600℃. The observed oxide scale at the interface between metallic substrate and anode, and, the weak bonding between the electrolyte and the cathode may be responsible for the high contact resistances. These observations also validate the presented equivalent circuit model. In addition, based on the improved equivalent circuit model, internal shorting current of metal-supported SOFCs due to electronic conduction was evaluated quantitatively.Furthermore, in order to evalue the dynamic properties of metal-supported SOFC aiming at mobile application, thermal cycle test was conducted as well. Throughout the thermal cycles, the open circuit voltage values retained relatively constant; however, impedance measurement indicated the cell performance deteriorated obviously. The relatively constant values of open circuit voltage suggest the electrolyte layer withstands thermal shock due to high thermal conductivity and excellent ductibility of the metal substrate. The observed degradation phenomina are most likely due to the thermal expansion coefficience mismatch and metal oxidation. These conclusions are consistent with the degradation mechanism discussed above by means of equivalent circuit model. This consistence also verifies the validation of the presented equivalent circuit model.To sum up, at present work the complete theoretical framework and feasiable diagnosis method were built for SOFC impedance diagnosis. Furthermore, the diagnosis results at present work offer precondition and theory foundation for performance optimization and reliability improvement of metal-supported SOFCs, which subsequently speeds up the commercialization process of metal-supported SOFCs.更多还原