Spin-State Tuning Enhances PrFeO3-δ Oxygen Reaction

Solid oxide electrolysis cells (SOECs) offer a route for efficient energy conversion and storage by converting renewable electricity into storable chemical fuels through high-temperature carbon dioxide electrolysis. However, sluggish oxygen evolution reaction (OER) at the anode poses a challenge due to its complex four-electron transfer process.

Perovskite oxides are regarded as promising candidates for SOEC anodes due to their high mixed ionic-electronic conductivity and tunable electronic structures. Studies have revealed a volcano-shaped correlation between the occupancy of the 3d electron with e_g symmetry in perovskite oxide and intrinsic OER activity in alkaline solution. However, the intrinsic connection between e_g occupancy and high-temperature OER activity remains unclear.

In a study published in Journal of the American Chemical Society, Assoc. Prof. SONG Yuefeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences, along with Prof. WANG Guoxiong from Fudan University, developed a series of alkaline-earth-metal-doped perovskites, Pr_0.5Ae_0.5FeO_3−δ (Ae = Ca, Sr, Ba, labeled as PCF, PSF, PBF), to investigate the impact of electronic structure tuning on high-temperature OER performance.

Researchers found that the OER activity increased with larger dopant ionic radius. They showed that the PBF achieved a current density of 3.33 A cm⁻² at 2.0 V and 800 °C.

Detailed analyses revealed that alkaline earth metal doping enhanced Fe 3d-O 2p hybridization, lowered charge-transfer energy, and promoted oxygen ions migration and surface spillover, accelerating the OER process. Moreover, magnetic measurements showed that Ba doping induced a spin-state transition from high-spin Fe³⁺ (t_2g³e_g²) to low-spin Fe⁴⁺ (t_2g⁴e_g⁰), resulting in reduced e_g occupancy and accelerated oxygen kinetics.

"Our study establishes spin-state tuning as a key strategy to boost high-temperature OER activity, and provides guidance for electronic structure engineering in the design of advanced SOEC anode materials," said Dr. SONG.