Entropy and Composition Regulations of Air Electrodes Enable Efficient Oxygen Reduction and Evolution Reactions for Reversible Solid Oxide Cells

Abstract One of the urgent challenges for efficient energy storage/conversion devices is the poor electrocatalytic activity and reversible operation capability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of the air electrodes. Recently, tremendous efforts of high‐entropy air electrodes are devoted, yet the performance enhancement is often ascribed to the high‐entropy. Herein, the effects of the increase of configurational entropy and the selection of specifically doped elements are investigated on the electrochemical performance of the electrodes. These results suggest that the selection of doped elements may contribute more to enhancing the electrocatalytic activity and stability of air electrodes when compared with the increase of the configurational entropy. Accordingly, the optimized medium‐entropy Pr 1/2 Ba 1/6 Sr 1/6 Ca 1/6 CoO 3‐δ (PBSCC) electrode shows superior electrocatalytic activity and stability for ORR and OER. A reversible solid oxide cell utilizing PBSCC demonstrates exceptional electrochemical performance, conveying a peak power density of 2.01 W cm −2 in the fuel cell mode and a current density of 1.40 A cm −2 in electrolysis mode (under 50% H 2 O humidified H 2 at 1.3 V) at 750 °C, while maintaining excellent cyclable operation stability for over 115 h.