A Broad Stability Investigation of Nb-Doped SrCoO_2.5+δas a Reversible Oxygen Electrode for Intermediate-Temperature Solid Oxide Fuel Cells

Abstract

The present work reports a systematic study on the structural, thermal, electrical and electrochemical stability of SrCo<sub>1–x</sub>Nb<sub>x</sub>O<sub>2.5+δ</sub> 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°C and a reversible oxygen redox reaction at 350°C. The conductivity of this material is p-type and also exhibits a peak at 350°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<sub>2</sub> dissociation step. Altogether, the material is thermally stable and oxygen redox reversible below 700°C, above which a catalytically less active brownmillerite SrCoO<sub>2.5</sub> is formed.