High-Entropy Perovskite Air Electrodes: Combined DFT–AIMD and Experimental Insights into Reversible Oxygen Evolution Reaction/Oxygen Reduction Reaction Activity

Despite their high bidirectional energy efficiency, the advancement of reversible solid oxide cells (R-SOCs) is constrained by the limited catalytic activity and durability of bifunctional air electrodes governing the oxygen reduction reaction/oxygen evolution reaction. First-principles calculations (density functional theory + U/ab initio molecular dynamics (AIMD)) were conducted to uncover the structure-property relationships in high-entropy perovskites La_0.2Pr_0.2Ba_0.2Sm_0.2Sr_0.2Co_0.8M_0.2O_3-δ (M = Cu, Fe) as air electrodes for R-SOCs. Explicitly disordered supercells revealed composition with induced structural distortions affecting local octahedral environments, while DFT-optimized lattice parameters in excellent agreement with X-ray diffraction data (error < 0.5%) have been achieved. Fe-/Cu-doped material shows a metallic character supporting good electronic conductivity. The O 2p band center location correlates with structural stability (cohesive energy), yielding high (3.19 eV) and low (1.56 eV) oxygen vacancy formation energies for Fe- and Cu-doped materials, respectively. Consistently, experimental results confirm that Fe-doping enhanced structural and thermal stability, while Cu-doping reveals an ease in oxygen vacancy creation with high reactivity. Diffusion analyses using the climbing image nudged elastic band, SoftBV, and AIMD revealed both open and closed oxygen pathways, governed by local bottleneck geometry and disorder, with Fe-doping exhibiting more continuous channels, as confirmed by a higher oxygen diffusion coefficient in AIMD simulation. Electrochemical impedance spectroscopy measurements demonstrate a defect-creation-dominated electrochemical response for Cu-doped material, while a more diffusion-controlled behavior with comparatively stable impedance evolution has been noticed for Fe-doped perovskite. Finally, the O₂ adsorption calculations identified Co sites as the most catalytically active, with adsorption energies of -1.98 and -1.65 eV for Fe- and Cu-doped materials, respectively. Together, these insights highlight the critical role of configurational entropy in fine-tuning electronic structure, defect formation, and oxygen transport for high-performance bifunctional electrodes.