Oxygen diffusion and surface exchange coefficients measurements under high pressure: Comparative behavior of oxygen deficient versus over‐stoichiometric air electrode materials

Abstract

Mixed ionic electronic conductors (MIECs) oxides are used as electrode materials for solid oxide cell (SOC) application, as they combine high electronic conductivity as well as high oxygen diffusivity and oxygen surface exchange coefficients. The ionic transport properties can be directly determined thanks to the isotopic exchange depth profiling (IEDP) method. To date, the reported measurements have been performed at ambient pressure and below. However, for a higher efficiency of hydrogen production at the system level, it is envisaged to operate the cell between 10 and 60 bar. To characterize the MIEC oxides properties in such conditions, an innovative setup able to operate up to a total pressure of 50 bar and 900°C has been developed. The main goal of this study was to compare the behavior of two types of reference materials: the oxygen deficient La‐Sr‐Fe‐Co perovskites, and the overstoichiometric lanthanide nickelates Ln2NiO4+δ (Ln = La, Pr, Nd). Diffusion and surface exchange coefficients obtained under 6.3 bar of oxygen are measured and their evolution discussed in light of the change in oxygen stoichiometries. This analysis allows better understanding of the dependency of the surface exchange coefficient with the oxygen partial pressure.