Performance degradation analysis of solid oxide fuel cells using dynamic electrochemical impedance spectroscopy

The commercial application of solid oxide fuel cells (SOFCs) is now facing the challenge caused by limited lifetime and durability. More in-depth understanding and scientific evaluation of the complex and coupled performance degradation mechanisms become a priority. In this study, a quantitative evaluation method is established based on dynamic electrochemical impedance spectroscopy (DEIS) measurements under different DC biases. The contributions of ohmic resistance and different polarization resistances to the overall performance degradation are separately determined through coupled distribution of relaxation time (DRT) analysis, equivalent circuit model (ECM) fitting and integral voltage loss calculation. This method is used to investigate the performance degradation of a single cell which is operated under galvanostatic mode for more than 1000 h. Precise contributions of individual processes to the overall degradation are quantitatively determined. Afterwards, post-test characterization on electrode microstructures is provided to support the impedance-based analysis results. In addition, the results are compared with our previously reported analysis of initial-stage rapid performance degradation. Since the proposed method is based on DEIS measurements, it can be further applied to performance degradation analysis of practical stacks as well as other electrochemical devices.