大尺寸固体氧化物燃料电池的电极过程解析方法

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

电化学阻抗谱(Electrochemical Impedance Spectroscopy,EIS)作为一种原位/非原位的电化学表征技术,在固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)尤其是小尺寸电池的研究中得到了广泛应用,而工业大尺寸电池的EIS研究较少且大多基于小尺寸电池的研究结果。本文对工业尺寸(10 cm×10 cm)阳极支撑平板式SOFC搭建了EIS测试系统,并改变电池运行温度、阳极/阴极气体组分,对该电池进行了系统的EIS测试,而后采用不基于先验假设的弛豫时间分布法(Distribution of Relaxation Times,DRT)对EIS数据进行解析。通过比较分析不同条件下的DRT结果,揭示了DRT中各特征峰与电池中具体电极过程的对应关系。与小尺寸电池相比,由于大尺寸电池的有效面积较大且入口流量较小,气体转化过程在大尺寸电池中不容忽视。本文通过解析EIS实现了对工业大尺寸SOFC单电池中各项电极过程的分辨,该方法及结果能够进一步应用于SOFC原位表征、在线监测以及衰减机理等相关研究。

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.