High-Entropy Engineering of Air Electrodes: A Game-Changer for Durable and High-Performance Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (R-PCCs) represent one of the most promising energy conversion technologies, enabling efficient interconversion between electrical and chemical energies at intermediate temperatures (400–700 °C). However, the lack of air electrodes with high catalytic activity and stability remains the primary bottleneck for their commercialization. This work presents a novel high-entropy perovskite oxide, BaCo 0.2 Fe 0.2 Y 0.2 Ni 0.2 Cu 0.2 O 3-δ (HE), as an advanced air electrode for R-PCCs. The lattice distortion effect effectively lowers the formation energy of the oxygen vacancy in this HE, significantly increasing the oxygen vacancy concentration and ORR/OER activity. Furthermore, the increased configurational entropy effectively suppresses atomic segregation and substantially improves the thermal and chemical stability of this oxygen electrode in reversible operation. When employed as an R-PCC air electrode, the HE demonstrates exceptionally low polarization resistance (0.085 Ω cm 2 at 700 °C) and remarkable stability during extended operation (100 h) and cycling tests (50 cycles in EC and FC modes). This study validates the entropy engineering strategy as a highly promising approach for developing high-performance and durable air electrodes for R-PCC applications.