High‐Entropy Co‐Based Oxygen Electrodes with Enhanced Thermomechanical Compatibility for Reversible Protonic Ceramic Cells

Abstract Reversible protonic ceramic cells (R‐PCCs) are a kind of distinguished long‐time energy conversion and storage device. The utilization of oxygen electrodes is vital to achieve high electrochemical performances for R‐PCCs, demanding high catalytic activity toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and appropriate thermal expansion coefficients (TEC). Herein, novel high‐entropy perovskites Pr 0.2 Ba 0.2 Sr 0.2 La 0.2 Nd 0.2 MeO 3‐δ (Me = Co, Fe, Mn) are explored. Pr 0.2 Ba 0.2 Sr 0.2 La 0.2 Nd 0.2 CoO 3‐δ (PBSLNC) exhibits a TEC of 12.02 × 10 −6 K −1 , which is thermomechanical compatible with BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3‐δ (BCZYYb) electrolyte. The cell with PBSLNC electrode delivers a peak power density of 0.87 W cm −2 in fuel cell (FC) mode and a current density of −1.39 A cm −2 at 1.3V and 650 °C under H 2 O electrolysis (EC) mode. The R‐PCCs with PBSLNC electrode also achieve a distinguished current density of −1.45 A cm −2 at 1.3 V and 700 °C under CO 2 ‐H 2 O co‐electrolysis condition. Moreover, the R‐PCCs with PBSLNC electrode demonstrate exceptional stability for 150 h in both FC and EC modes, 96 h in H 2 O‐CO 2 co‐electrolysis mode, and 100 h (10 cycles) in reversible mode. This research provides a novel oxygen electrode for R‐PCCs, as well as a strategy to design efficient Co‐based oxide catalysts with low TEC for advanced R‐PCCs.