A‐Site High‐Entropy Engineering of Oxygen Electrode: A Promising Route to Durable and Active Reversible Solid Oxide Cells

Reversible solid oxide cells (RSOCs) are promising for their highly efficient power-fuel interconversion and serve as a critical technology for building a carbon-neutral energy ecosystem. However, their widespread implementation is impeded by insufficient electrocatalytic activity and stability of conventional oxygen electrodes. Here, we design a high-entropy single-phase perovskite, Pr_0.2Nd_0.2Sm_0.2Ba_0.2Sr_0.2CoO_3-δ (PNSBSC), engineered from Sm_0.6Sr_0.4CoO_3-δ (SSC), to overcome the classic activity-stability trade-off in perovskite oxides. A PNSBSC-based button cell delivers a peak power density of 2.06 W cm^-2 in fuel cell mode and a high current density of 2.54 A cm^-2 at 1.3 V in electrolysis mode (50% H₂O) at 800 °C. The cell also demonstrates exceptional stability, sustaining 120 h of continuous operation in both modes and three reversible cycles at 700 °C without performance degradation. Its scalability and robustness are further verified using a large-area cell (30 W output, >80 h stability) and by sustaining a notable 40 A electrolysis current at 1.3 V (80% H₂O, 750 °C). First-principles calculations corroborate the enhanced activity and stability, which are attributed to the high-configurational-entropy design. This work establishes entropy engineering as a viable paradigm for developing high-performance and durable electrodes for advanced RSOCs.