A Framework for Characterizing Commercial Solid Oxide Electrolysis Stacks Using Electrochemical Impedance Spectroscopy and Equivalent Circuit Modeling

Electrochemical impedance spectroscopy (EIS) is a powerful diagnostic tool for analyzing solid oxide electrolysis cells (SOECs). While EIS measurements on single-cell level are commonplace, implementation of EIS on stack level remains limited. Here, we report a framework for analyzing stack-level EIS data. Analysis of the collected impedance data comprises Kramers-Kronig transformations, distribution of relaxation times (DRT), and analysis of the difference of impedance spectra (ADIS). The DRT and ADIS results were used as input parameters for the complex non-linear least squares (CNLS) fitting procedure and the validity of the chosen equivalent circuit model was confirmed by reconstruction of Nyquist-, Bode-, DRT-plots, and the individual electrochemical contributions of the fitted data. The developed framework was successfully implemented on a commercial 75-cell SOEC stack (TSP-1) from Haldor Topsoe.