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

ABSTRACT 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 0.2 Nd 0.2 Sm 0.2 Ba 0.2 Sr 0.2 CoO 3‐δ (PNSBSC), engineered from Sm 0.6 Sr 0.4 CoO 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% H 2 O) 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% H 2 O, 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.