Doping-Enabled Symmetry Control in BaCoO₃ for Enhanced Oxygen Reduction Reaction

Area of Science:

• Materials Science
• Electrochemistry
• Solid State Chemistry

Background:

• Perovskite oxides are crucial for solid oxide fuel cell (SOFC) cathodes.
• BaCoO3 (BCO) derivatives offer potential as mixed ionic-electronic conductors.
• The hexagonal phase of BCO limits performance, necessitating transformation to the cubic phase.

Purpose of the Study:

• To investigate the effect of doping on the hexagonal-to-cubic phase transition in BCO.
• To determine how crystal structure influences oxygen reduction kinetics in BCO derivatives.
• To identify optimal dopants for stabilizing the cubic phase and enhancing SOFC cathode performance.

Main Methods:

• Systematic synthesis and characterization of seven BCO compositions (undoped, Sc, Y, Zr, Hf, Nb, Ta doped).
• Analysis of the correlation between crystal structure (hexagonal vs. cubic) and oxygen reduction kinetics.
• Evaluation of electrochemical performance, specifically polarization resistance.

Main Results:

• The hexagonal-to-cubic phase transition is the key factor for oxygen reduction kinetics.
• Tantalum (Ta) doping was most effective in promoting the cubic phase.
• Ta-doped BCO achieved a low polarization resistance of ≈0.004 Ω cm² at 650 °C.
• Cubic symmetry facilitated oxygen ion transport, vacancy formation, and surface adsorption.

Conclusions:

• Chemical doping effectively stabilizes the cubic phase of BCO.
• Crystal symmetry is a critical design parameter for tailoring perovskite oxide functionality.
• Optimized BCO derivatives show promise for advanced electrochemical energy conversion devices like SOFCs.