A/B‐Site Dual Doping of YbFeO 3 ‐Based Orthorhombic Perovskites for Activity‐Stability Balanced Air Electrodes in Reversible Solid Oxide Fuel Cells

ABSTRACT Reversible solid oxide fuel cells (RSOCs) require air electrodes that are active for both oxygen reduction and oxygen evolution reactions while resisting degradation under operating conditions. YbFeO 3 (YbFO) offers a robust orthorhombic perovskite framework with moderate thermal expansion, but its intrinsic electrode activity remains limited. Here, we report a series of YbFO‐based orthorhombic perovskite air electrodes through A/B‐site dual doping. The optimized Yb 0.7 Sm 0.3 Fe 0.4 Co 0.6 O 3 (YbSFC) exhibits a low polarization resistance of 0.08 Ω cm 2 at 700°C and a suitable thermal expansion coefficient of 12.22 × 10 −6 K −1 . In proton‐conducting RSOCs, the YbSFC air electrode delivers a peak power density of 1.12 W cm −2 in fuel cell mode and a current density of 2.55 A cm −2 at 1.3 V in electrolysis mode at 700°C. The cell also operates stably for over 200 h in fuel cell mode. In addition, when applied in oxygen‐ion‐conducting RSOCs, the same air electrode reaches a peak power density of 0.93 W cm −2 in fuel cell mode and a current density of ‐0.96 A cm −2 at 1.3 V in electrolysis mode at 800°C. These results show that YbFO‐based orthorhombic perovskites can serve as effective and durable air electrodes for RSOCs.