Designing Fe-Based Oxygen Catalysts by Density Functional Theory Calculations

A cheap and effective oxygen catalyst can find a variety of applications including cathodes for solid oxide fuel cells, oxygen transport membranes, cathodes for metal air batteries, and catalysts for thermal water splitting. This work studies BaFeO3 (BFO)-based perovskites as oxygen catalysts from density functional theory calculations by substituting the A and B sites of the BFO perovskite structure. Na, K, Rb, Ca, Sr, Y, La, and Pb are substituted into the A site, and Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, Ag, In, and Ce are substituted into the B site. We point out that there is a trade-off among stability, electronic conductivity, and ionic conductivity, where the material selection needs to be based on the maximization of the desired property for a given application. Specifically, the calculation results show that the A site substitution with Na and K lowers the vacancy formation energy while preserving the electronic conductivity. However, the introduction of such elements may destabilize the cubic perovskite lattice structure. Alkaline-earth elements, Ca and Sr, have relatively small impact on the ionic diffusion but may enhance the electronic conductivity. In addition, La substitution stabilizes the cubic perovskite phase and lowers the oxygen migration barrier, but it compromises the electronic conductivity and vacancy concentrations. Regarding the B site substitution, Sc, Y, Nb, and Ce stabilize the cubic perovskite structure, although they sacrifice performance. However, Ni, Cu, Zn, and Ag substitution may increase the electronic conductivity and reduce the vacancy formation energy at the expense of stability.