Modeling of solid oxide cells with mixed ionic electronic conductor electrolytes using a unified electrochemical potential model

Mixed ionic electronic conductors (MIEC) ceramic solid electrolytes have been widely used in solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs). Existing full-cell models are typically difficult to capture the oxygen chemical potential (OCP) profile in electrodes and have poor generality. However, the OCP transition by overpotential is closely related to both degradation near the electrodes of SOECs and the drop in open-circuit voltage (OCV) of SOFCs. Based on phenomenological equations, we develop a unified mathematical framework for charge transport in solid oxide cells (SOCs). Our model quantifies the OCP in electrodes by directly relating the local OCP to the electrode overpotential, thus providing insights into the relationship between overpotential and OCP. Our results show that there is a ubiquitous OCP transition in the electrodes and that is extremely sensitive to electrode overpotentials. The oxygen potential peaks and valleys found in the Yttria-stabilized Zirconia (YSZ) of the multilayer electrolyte SOEC provide new opportunities to understand degradation phenomena in the relevant literature. In addition, our predictions of leakage current and OCV illustrate the generality of the model for cell performance pre diction. The results may offer new methods and insights for predicting the performance and understanding the degradation mechanisms of SOCs with MIEC electrolytes or multilayer electrolytes.