Increased activity in the oxygen evolution reaction by Fe4+-induced hole states in perovskite La1−xSrxFeO3

Abstract

Perovskite transition metal oxides are promising non-precious metal electrocatalysts for promoting the oxygen evolution reaction (OER) in many electrochemical energy conversion devices. This work reports a systematic study of the relation between the electronic structure and OER performance of perovskite La_1−xSr_xFeO₃ (0 ≤ x ≤ 1). The partial substitution of La for Sr in LaFeO₃ results in the oxidation of Fe³⁺ to Fe⁴⁺ and substantially enhances OER activity. A comprehensive X-ray spectroscopic study reveals a strong correlation of the enhanced OER activity with these Fe⁴⁺ states. The presence of Fe⁴⁺ leads to a stronger Fe–O bond due to stronger Fe 3d–O 2p orbital hybridization and shifts the energy position of the valence band (VB) to E_F. Such an electronic modulation optimizes the surface adsorption energetics of *OH intermediates, contributing to faster OER kinetics. Furthermore, a new unoccupied state is created at ∼0.9 eV below the conduction band. This hole state reduces the energy barrier for electron transfer from 1.34 eV to 0.44 eV, thereby facilitating charge transfer at the interface. The Fe⁴⁺-induced electronic states responsible for higher OER activity have implications for the understanding of structure–activity relationships in other Fe-based electrocatalysts such as highly active Fe-doped NiOOH.