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

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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.