DFT insights on iron-based layered perovskites as oxygen catalysts

Abstract

Density Functional Theory (DFT)-derived electronic descriptors are key to accelerating the design of effective ORR/OER catalysts. The O 2p-band center, in particular, is a robust descriptor of catalytic activity in perovskite oxides. This study examines the O 2p-band center in Fe⁴⁺ perovskite-type layered oxides, focusing on the Ruddlesden Popper (RP) phases Sr₂FeO₄ and Sr₃Fe₂O_7, as well as the high-Tc superconductor YSr₂Cu₂FeO_8. The analysis emphasizes trends driven by compositional modifications. The O 2p-band centers of Sr_2–2xLa_2xFeO₄ and Sr_3–3xLa_3xFe₂O₇ (0 < x < 1) correlate linearly with the Fe oxidation state, and span a wide energy range (–1.2 eV to –4.7 eV with PBE+U; –1.9 eV to –4.7 eV with SCAN). Partial substitution of Fe with 3d transition metals (TM) in Sr₂Fe_7/8xM_1/8O₄ shifts the O 2p band center, with the more electronegative TMs bringing it closer to the Fermi level. RP-Sr₂FeO₄ exhibits remarkable tunability of the O 2p-band center, enabling the compositionally driven design of oxygen catalysts with potentially improved activity–stability balance. In contrast, YSr₂Cu₂FeO_7+δ (0 < δ < 1) shows no correlation between the O 2p-band center and Fe oxidation states, likely due to a change in Fe coordination from octahedral (δ = 1) to tetrahedral (δ = 0). The O 2p-center values (–0.9 eV to –1.3 eV with PBE+U; –1.5 eV to –2 eV with SCAN) suggest that YSr₂Cu₂FeO_7+δ could potentially catalyze the ORR/OER, though stability over operation time remains a challenge.