Efficient energy conversion and storage technologies are critical for achieving China's carbon peak and carbon neutrality goals. Solid oxide electrolysis cells (SOECs) offer a promising route 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 major 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. Previous studies have revealed a volcano-shaped correlation between the occupancy of the 3d electron with eg symmetry in perovskite oxide and intrinsic OER activity in alkaline solution, with peak activity occurring at a near-unity eg occupancy. However, the intrinsic connection between eg occupancy and high-temperature OER activity has remained unclear.
Spin-state tuning in PrFeO3-δ perovskite for high-temperature oxygen evolution reaction (Image by YU Jingcheng)
In a study published in Journal of the American Chemical Society, Assoc. Prof. SONG Yuefeng from the State Key Lab of Catalysis（SKLC), along with Prof. WANG Guoxiong from Fudan University, developed a series of alkaline-earth-metal-doped perovskites, Pr0.5Ae0.5FeO3−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 OER activity increases with larger dopant ionic radius. They showed that the PBF achieves a current density of 3.33 A cm−2 at 2.0 V and 800 °C.
Detailed analyses revealed that alkaline earth metal doping enhances Fe 3d-O 2p hybridization, lowers charge-transfer energy, and promotes oxygen ions migration and surface spillover, thereby accelerating the OER process. Moreover, magnetic measurements showed that Ba doping induces a spin-state transition from high-spin Fe3+ (t2g3eg2) to low-spin Fe4+ (t2g4eg0), resulting in reduced eg occupancy and accelerated oxygen kinetics.
"Our study establishes spin-state tuning as a key strategy to boost high-temperature OER activity, and provides fundamental guidance for electronic structure engineering in the design of advanced SOEC anode materials," said Dr. SONG.
