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Reversible protonic ceramic electrochemical cells (R-PCECs) are a promising option for efficient and low-cost generation of electricity and hydrogen. Commercialization of R-PCECs, however, hinges on the development of highly active and robust air electrodes. Here, we report an air electrode consisting of PrBa_0.8Ca_0.2Co₂O_5+δ and in situ exsolved BaCoO_3−δ nanoparticles (PBCC–BCO) that shows minimal polarization resistance (∼0.24 Ω cm² at 600 °C) and high stability when exposed to humidified air with 3−50% H₂O. An R-PCEC utilizing PBCC-BCO demonstrates remarkable performances at 600 °C: achieving a peak power density of 1.06 W cm^–2 in the fuel cell mode and a current density of 1.51 A cm^–2 at 1.3 V in an electrolysis mode. More importantly, the R-PCECs demonstrate an exceptionally high durability over 1833 h of continuous operation in the electrolysis mode. This work offers an efficient …