An Analysis of Capacitive Contributions of the Cell Impedance during High-Temperature CO2 and Co-Electrolysis

Abstract

The electrolysis of steam (H2O) and/or carbon dioxide (CO2) is a sustainable way to produce hydrogen (H2) and/or carbon monoxide (CO). In research and development the processes occurring at the electrodes in the electrolysis cells are usually analyzed by electrochemical impedance spectroscopy (EIS). The spectra are evaluated by equivalent circuit models (ECMs) consisting of resistances, capacitances and/or inductances. For the further assignment of the processes, the spectra are measured at varied operating conditions. However, in many cases only the dependencies of the resistances resulting from the ECM are discussed in detail. In this publication, we examined the capacitive contributions to the impedance of the electrolysis of H2O and CO2 and their dependencies on operating conditions. In comparison, the capacitances of CO2 and co-electrolysis only differ in the low frequency range, which could describe an adsorption process additional to the reported gas diffusion impedance.