Electro-chemo-mechanical analysis of a solid oxide cell based on doped ceria

Abstract

Doped ceria has been investigated as an electrolyte material for solid oxide cells (SOC) for several decades due to its high ionic conductivity. However, ceria is reduced under fuel conditions in SOCs and becomes a mixed ionic-electronic conductor (MIEC). One of the issues arising is the chemical expansion of the electrolyte, which is a function of the oxygen activity μO2 inside the electrolyte and therefore inhomogeneous across the electrolyte thickness. A one-dimensional model that enables the calculation of elastic stresses in the cell on the basis of the cell geometry and materials properties is developed for both fuel cell and electrolysis operation. Ceria is subjected to a decreased oxygen activity at the interface to the fuel electrode during electrolysis operation, leading to substantial mechanical stresses in the electrolyte layers. Cell failure is observed under high electrolysis currents for a high-performance cell based on a doped-ceria electrolyte. We model the electro-chemo-mechanically-induced elastic stresses in the multilayer system of the cell and show that it peaks for operation at 750 °C and high current densities, in agreement with the observed onset of cell failure. Furthermore, the influence of the cell constraints on the elastic stresses is discussed for four different constraint cases.