Exploring electrochemical impedance spectroscopy to identify and quantify degradation in commercial solid oxide electrolysis stacks

Abstract

In this work, we present a case where electrochemical impedance spectroscopy (EIS) on stack level enabled the identification of degradation and failure mechanisms in a 75-cell solid oxide electrolysis cell (SOEC) stack from Topsoe. In a blind test, a defective stack (stack not passing the quality control specifications) prone to degradation was investigated with EIS. The type of stack defects was not known a priori. The purpose of the stack EIS experiment was hence to serve as a proof-of-concept of using EIS on the stack level for identifying degradation mechanisms. An appropriate equivalent circuit model was applied and fitted to the experimentally obtained EIS data, which enabled the quantification of the different electrochemical contributions. We hereby identified which electrochemical contribution(s) to the overall stack resistance caused the stack to degrade. Furthermore, the data was plotted in a degradation space format, which further strengthened the identification of the cause of degradation. In this work, we are exploring and utilizing the potential of advanced EIS characterization and analysis; thereby successfully identifying some of the degradation and failure mechanisms taking place in the SOEC stack. This detailed type of degradation analysis has, to the best of my knowledge, not previously reported on the commercial stack level.