Identification of Electrode Process in Large-size Solid Oxide Fuel Cell

Abstract

Solid oxide fuel cell (SOFC) with high energy conversion efficiency, low pollutant emission, and good fuel adaptability has witnessed rapid development in recent years. However, the commercialization of SOFC remains limited by constraints of performance and stability. Electrochemical impedance spectroscopy (EIS) can distinguish ohmic impedance caused by ion transport from polarization impedance related to electrode reaction; it has been widely used in the research of performance and stability as an efficient on-line characterization technology. The physical/chemical processes involved in EIS overlap significantly and can be decomposed by the distribution of relaxation times (DRT) method which does not depend on prior assumptions. Since industrial large-size SOFC is vulnerable to the influence of inductance and disturbance when testing EIS, its EIS analysis is rarely studied and mostly based on the research results of cells with smaller electrode active area. To further elucidate the impedance spectrum of industrial large-size SOFC under actual working conditions, the EIS of industrial-size (10 cm × 10 cm) anode-supported planar SOFC was systematically tested over a broad temperature and anode/cathode gas composition range. First, the quality of the impedance data was examined by performing a Kramers-Kronig test. The residuals of real and imaginary data were within the range of ±1%, indicating good data quality. Then, the DRT method was adopted to parse the EIS data. By comparing and analyzing the DRT results under different conditions, the corresponding relationships between each characteristic peak in the DRT results and the specific electrode process in the SOFC were revealed. The characteristic frequencies were separated into 0.5-1, 1-30, 10-30, 1 × 10 2 -1 × 10 3 , and 1 × 10 4 -3 × 10 4 Hz regions, corresponding to gas conversion within the anode, gas diffusion within the anode, oxygen surface exchange reaction within the cathode, charge-transfer reaction within the anode, and oxygen ionic transport process, respectively. In this study, the identification of each electrode process in industrial large-size SOFC is realized, indicate that the gas conversion process in large-size SOFC with larger active area and smaller flows cannot be ignored compared with the cells with smaller electrode active area. The method followed and the results obtained have a universal quality and can be applied to the in situ characterization, online monitoring, and degradation mechanism research of SOFC, thus laying a foundation for the optimization of the performance and stability.

Effects of Ceria on the Oxygen Reduction Activity and Thermal Cycling Stability of BaCo0.4Fe0.4Zr0.1Y0.1O3−δ Cathode for Solid Oxide Fuel Cells

“…The ORR process contains multielementary steps, including gas diffusion from the mainstream to the electrode surface, chemical adsorption, dissociation, charge transfer, and bulk ionic transportation to the electrolyte/electrode interface. So, to clarify the substeps involved in the whole ORR, the EIS of symmetric cells were tested at different oxygen pressures ( P O 2 ), and the results are shown in Figure a,c; the resulted EIS are deconvoluted using the distribution of relaxation times (DRT) method considering different relaxation times of elementary steps − (Figure b,d). Similar to temperature depending on EIS response, the ASR decreases with the increased oxygen partial pressure.…”

Study of Operating Conditions for High Efficiency and Anode Safety of Industrial-Size Solid Oxide Fuel Cell

“…电池两侧 采用银网集流, 并从两侧端板上引出电流引线和电压引 线, 连接至电子负载(Itech IT8514C＋)和电化学工作站 (Zahner Zennium), 从而测试电池的电化学性能. 电池 密封及接线等具体测试方法可参考本课题组之前的工 作 [36][37] .…”

Evolution of Electrochemical Characteristics of Solid Oxide Fuel Cells During Initial-Stage Operation

“…目前已经建立的 EIS 解析方法包括等效电路拟合法 (ECM)、 阻抗差异分析法(ADIS)、 弛豫时间分布法(DRT) 等. 在本课题组之前的工作中, 已经通过 DRT/ECM 方 法实现了对纽扣电池 [8] 、工业大尺寸电池 [9] 中各项电极 过程的分辨, 并在此基础上基于带载 EIS 解析初步研究 了电池性能演变机制 [10] . 广泛的实验测试结果表明, SOFC 在运行初期(约前 100 h)的性能演变最为显著和复 杂: 部分电池的性能在这一阶段迅速降低 [10][11] , 也有部 分电池的性能在这一阶段先有所上升、之后逐渐降 低 [12][13] .…”

“…本工作采用实 验室自编程软件进行 DRT 分析, 基本算法为 Tikhonov 正则化方法, 选取正则化因子为 0.001. 基于本课题 组 [8][9] 及其他研究机构 [28][29] 对相同结构电池的敏感性分 析实验结果, DRT 中各特征峰与电极过程的对应关系已 基本明确, 如表 1 所示. 表 1 DRT 中各特征峰对应的电极过程 Table 1 The electrode process corresponding to each characteristic peak in DRT Peak…”

“…, 除了其特征弛豫时间处的主峰 P4 之外, 对更 小弛豫时间的特征峰(P3、P2 等)也会有一定影响, 但是 影响程度相对较小. 此外, 由于纽扣电池几何尺寸较小, 阳极表面 H 2 -H 2 O 组分分布比工业尺寸电池更为一致, 因此纽扣电池的 DRT 中气体转化过程(P5)不显著[9] , 在…”