Bulk and Surface Properties of New Materials for Solid Oxide Fuel Cell Electrodes

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Further improvement of the efficiency and thermal stability of solid oxide fuel cells (SOFCs) requires alternative electrode materials that allow to lower the operating temperature of fuel cells to 600-800 C. Two innovative new classes of cathode and anode materials with promising electronic/ionic conductivity and catalytic activity at lower temperatures are layered cobalt oxide compounds with YBaCo4O7 structure and Sr2MgMoO6-based double-perovskites, respectively. The electronic/ionic and catalytic properties of both compounds can be tuned by substitution with a wide variety of elements on the different sublattices, which also modifies their thermal phase stability. Another very promising strategy for improving solid oxide fuel cell performance is to use liquid Sn anodes high-temperature SOFCs. They are distinguished by high robustness and low sensitivity to fuel contaminations.The overall aim of this project is to obtain a better understanding of the bulk and surface properties of these new classes of SOFC anode and cathode materials on an atomistic level by means of first-principles calculations based on density functional theory. By studying the interaction with oxygen and small fuel molecules (H2, CH4, CO) we will simulate the processes that occur during SOFCs working conditions on the cathode and anode sides, respectively. We will focus on the thermodynamic stability of bulk phases and surface structures and search for the most stable surface configurations and compositions in different environments at given temperature and partial pressures. The influence of substituents on the electronic properties, on oxygen vacancy formation and on phase stability will be investigated. Insights into the kinetics of oxygen migration inside the bulk, on the surfaces and at the electrode/electrolyte interfaces shall be obtained by calculation of activation barriers. The mechanisms of these processes that govern the oxygen uptake at the cathode, the fuel oxidation at the anode and the phase stability at the electrode/electrolyte interfaces are still basically unknown. A better understanding shall contribute to a knowledge-based improvement of the chemical and thermal properties of these new classes of materials for future SOFC applications.