Oxygen Transport in Perovskite-Type Materials for SOFCs Cathodes: What Can We Learn from Quantum Mechanics

Effective, rational design of innovative, low-cost materials with high oxygen reduction reaction (ORR) catalytic activity at intermediate temperatures (ITs) requires a deep understanding of the underlying reaction mechanisms of oxygen incorporation and diffusion in solid oxide fuel cell (SOFC) cathodes.

We use state-of-the-art first-principles calculations in order to gain atomic scale insights into the relationships between composition, structure, and transport properties of traditional perovskite-type cathode materials ABO₃ (A=La, Sr; B=Mn, Fe, Co, Cr) and the new, promising Sr₂Fe_1.5Mo_0.5O_6-δ electrode. Specifically, we study the factors that govern bulk oxide ion diffusion in these materials, namely, the oxygen vacancy formation energy and migration barrier, as well as the surface features that allow the dissociation and incorporation of oxygen.

Beyond quantitative agreement with measurements, our results provide new insights into the origin of the observed material behavior. The electronic structure of the B-site transition metal, the A-site cation charge and the B-O bond nature are the main features that determine perovskite cathode performance. The subtle interplay of long-range electrostatics and local electronic effects is ultimately responsible for vacancy formation, ion and transport, and electronic conductivity. All these properties and processes can be fine-tuned by appropriate choices of A- and B-site constituent elements and aliovalent substitutions at each site. The ratio and nature of the additives are crucial for obtaining the desired performance.

Our findings provide foundational and systematic understanding of perovskite bulk and surface properties and of the emergent ORR performance so that new generations of effective SOFC cathodes can be developed.

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