Several mixed ionic-electronic conducting (MIEC) materials, e.g. (La,Sr)(Co,Fe)-based perovskites, exhibit excellent oxygen transport properties, namely fast chemical surface exchange and oxygen bulk diffusion, thus rendering them suitable candidates for applications such as fuel cell catalysts and oxygen permeation membranes. As the reduction of CO₂ emissions in coal or gas power plants is increasingly gaining attention, particularly membranes for oxygen separation based on such MIEC perovskite materials show promise for a future large-scale application in power plants.

In this presentation, several material systems are assessed with regard to their surface exchange kinetics and oxygen ion bulk diffusion properties. Porous perovskite layers with the chemical compositions La_0.68Sr_0.3FeO_3-δ and La_0.68Sr_0.3Co_0.2Fe_0.8O_3-δ (two solid oxide fuel cell (SOFC) cathode compositions) are characterized by electrochemical impedance spectroscopy (EIS). The chemical surface (k^d) and diffusion (D^d) coefficients of both materials are obtained as a function of temperature and pO₂ directly from EIS measurements performed on full anode-supported cells. This is achieved by a combined distribution of relaxation times and equivalent circuit impedance analysis method, which allows a highly resolved identification and deconvolution of each single polarization mechanisms contributing to the overall loss of the cell. This approach can also be extended to further MIEC materials, such as the state-of-the-art membrane perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ.

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1. Electrical and Oxygen Transport Properties of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ