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

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.