Spin-State Tuning in PrFeO_3-δ Perovskite for High-Temperature Oxygen Evolution Reaction

The electrocatalytic activity of perovskite oxides is fundamentally governed by their electronic structure. However, a deeper understanding of the relationship between the e_g electron occupancy and high-temperature oxygen evolution reaction (OER) performance in solid oxide electrolysis cells (SOECs) remains underexplored. Here, A-site doped Pr_0.5Ae_0.5FeO_3-δ (Ae = Ca, Sr, Ba) are constructed with exceptional high-temperature OER performance, and Pr_0.5Ba_0.5FeO_3-δ achieves a current density of 3.33 A cm^-2 at 2.0 V and 800 °C. X-ray absorption spectroscopy, ⁵⁷Fe Mössbauer spectroscopy, and magnetic susceptibility measurements reveal that alkaline earth metal doping induces a spin-state transition from high-spin Fe³⁺ (t_2g³e_g²) to low-spin Fe⁴⁺ (t_2g⁴e_g⁰), with reduced e_g occupancy, thus accelerating the charge transfer and oxygen transport in the OER process. This work sheds light on the critical role of the B-site Fe electronic structure in high-temperature OER performance and provides guidance for the rational design of Fe-based perovskites as SOEC anode materials.