Unveiling a Surface Electronic Descriptor for Fe-Co Mixing Enhanced the Stability and Efficiency of Perovskite Oxygen Evolution Electrocatalysts

The influence of cation mixing on the oxygen evolution reaction (OER) activity of a La_xSr_1-xCo_yFe_1-yO₃(LSCF) double perovskite is investigated using density functional theory (DFT) calculations. The O 2p band center (E_2p) has a good linear relation with the binding energy of the OER intermediate species when the chemical composition is varied by only the x or y value, but this relation is insufficient for describing the nonmonotonic behavior over the entire x and y ranges. Based on the projected density of states and wavefunction analysis, the minority spin d_xyelectrons of surface layer metal atoms are significant due to their stability, where the antibonding states between d_xyand the lattice oxygen p become occupied when Co atoms with one d electron more than Fe are present. Thus, by additionally considering the d_xyband center, a surface electronic descriptor (E_2p- 0.4E_dxy) excellently describes the binding energy of the OER intermediates and the stability against oxygen-vacancy formation, which also explains the enhanced OER stability and efficient Fe-Co mixing. Our study unveils the key mechanism of the excellent OER performance and high stability of previously reported LSCF materials as well as provides heterostructure engineering guidance for optimal surface electronic structures.