Current interrupt method for calculating the electrochemical impedance in a solid oxide electrolysis stack

Abstract

In this work the time domain response of Solid Oxide Electrolysis Cells (SOEC) to a current interruption was transformed into the frequency domain using a carrier function Laplace transform, which is fit to the experimental data using a MATLAB Complex Nonlinear Least Squares (CNLS) solver to obtain the complete impedance spectrum. The hardware implementation, consisting principally of a high-speed switch and a fast-logging Analog to Digital Converter (ADC), was assembled and tested using a calibration module to assess the accuracy, repeatability, and speed of acquisition of the prototype device as compared against a calibrated commercial impedance spectrometer. Additionally, the current interrupt device and commercial Frequency Response Analyzer (FRA) were used to acquire the impedance spectra of a four cell SOEC stack with a large, 300 cm², active cell area.