A novel cobalt-free perovskite oxide La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3-delta (LSFCN) has been synthesized and evaluated as oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The performance and stability of the LSFCN based RSOCs have been characterized in fuel cell and electrolysis modes, and the reversibility of the cells has been proven. In FC mode, the cell exhibits the maximum power density of 1.10 W cm(-2) at 800 degrees C, and a stable output under 0.7 V at 700 degrees C during 108 h. The performance and stability of the cell in electrolysis mode are also remarkable. An electrolysis current of 0.85 A cm(-2) is achieved at 750 degrees C with an applied voltage of 13 V. and no degradation as well as delamination are observed for the cell after 50 h electrolysis under voltage of 1.60 V (similar to 1.27 A cm(-2)) at 800 degrees C. The high performance of the LSFCN at both cathodic and anodic conditions may be attributed to the inherent high electrochemical activity of copper-iron based perovskites; and the incorporation of Nb5+ cations into perovskite lattice is responsible for the stability of LSFCN, which leads to the more stable crystal structure, lower thermal expansion coefficient and the reduced Sr segregation at surface. (C) 2016 Elsevier B.V. All rights reserved.