The present work reports a systematic study on the structural, thermal, electrical and electrochemical stability of SrCo1-xNbxO2.5+delta series as a potential reversible oxygen-electrode for intermediate-temperature solid oxide fuel cells. The identified best composition is x = 0.10, which exhibits a stable pseudo primitive cubic structure at <700 degrees C and a reversible oxygen redox reaction at 350 degrees C. The conductivity of this material is p-type and also exhibits a peak at 350 degrees C, implying that the electron hole conduction is closely associated with the oxygen nonstoichiometry. Electrochemical impedance spectroscopy analysis indicates a low polarization resistance rate-limited by a slower surface O-2 dissociation step. Overall, the material is thermally stable and oxygen redox reversible below 700 degrees C, above which a catalytically less active brownmillerite SrCoO2.5 is formed. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.