A High‐Entropy Composite Air Electrode with Dual‐Phase Exsolution for Efficient Reversible Proton Ceramic Cells

ABSTRACT Reversible proton ceramic cells (R‐PCCs) are attracting increasing attention as sustainable electrochemical devices that can switch between efficient power generation and steam electrolysis. However, their development is limited by the scarcity of air electrodes that can offer both fast oxygen/water conversion kinetics and robust structural stability. Herein, we introduce a high‐entropy composite air electrode that has been designed using an entropy‐driven dual‐phase exsolution approach and formulated as xNiO‐yCeO ₂ ‐Pr _0.2 La _0.2 Ba _0.2 Sr _0.2 Ca _0.2 Fe _0.2 Ni _0.15‐x Ce _0.05‐y O _3‐δ (N/C‐XFNC). The configurationally disordered perovskite matrix provides enhanced thermodynamic stability, while the in situ exsolution of NiO and CeO ₂ nanoparticles creates bifunctional catalytic sites. NiO promotes oxygen adsorption and dissociation, while CeO ₂ substantially strengthens water uptake and proton hydration. Combined experimental characterization and first‐principles analysis reveal that R‐PCCs equipped with the N/C‐XFNC electrode deliver markedly improved performance. It achieves a peak power density of 1.41 W cm ⁻² and a current density of −2.61 A cm ⁻² at 1.3 V in electrolysis mode at 650°C. Furthermore, the cells further sustain stable operation for over 800 h at 600°C, highlighting the structural resilience of the high‐entropy architecture. This work presents a generalizable design concept that leverages entropy engineering and controlled exsolution to create durable, high‐performance air electrodes for next‐generation R‐PCCs technologies.