A Reversible Perovskite Air Electrode for Active and Durable Oxygen Reduction and Evolution Reactions via the A-site Entropy Engineering

The performance of reversible solid oxide electrochemical cells (R-SOECs) is largely hindered by the insufficient electroactivity and poor durability of the bifunctional air electrodes, where the oxygen reduction and evolution reactions (ORR and OER) occur. Here, we report our findings in boosting the electrochemical activity and durability of an air electrode with Pr0.2Ba0.2Sr0.2La0.2Ca0.2CoO3-δ (PBSLCC) via an A-site entropy engineering. The PBSLCC electrode shows enhanced oxygen reaction activity and excellent durability compared to binary and ternary double perovskites (PrBaCo2O5+δ and Pr0.8Ba0.8Ca0.4Co2O5+δ, respectively). A low and nearly unchanged area-specific resistance of 0.042 Ω cm2 is achieved at 750 °C during the 225-h stability test. La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte-supported cells with the PBSLCC air electrode show remarkable performance at 800 °C, demonstrating a peak power density of 1.2 W cm−2 in the fuel cell mode, and a current density of −1.1 A cm−2 at 1.3 V in the electrolysis mode while maintaining the excellent cycling durability of 228 h at ±0.5 A cm−2 under humidified H2 (10% H2O). A bulk oxygen p-band center model is applied to verify that tailoring of the A-site entropy strongly influences the surface exchange coefficients (k*chem), leading to higher oxygen reaction activity of PBSLCC than the binary and ternary perovskites. This study opens a new class of high-entropy perovskites for the rational design of air electrodes for R-SOECs with high activity and durability.