Co-free La0.5Sr0.5Fe0.9Nb0.1O3-delta (LSFNb) perovskite oxide is synthesized by the sol-gel method. LSFNb oxide exhibits good chemical and structural stability in both oxidizing and reducing atmospheres. Therefore, symmetric cells with the configuration LSFNb/LSGM/LSFNb are prepared and the electrochemical performance is evaluated for both solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOEC) applications. The LSFNb symmetric electrode presents excellent catalytic activity in both SOFC and SOEC modes. At 850 degrees C, the peak power density of the symmetric cell reaches 1157 mW cm(-2) in SOFC mode, while the current density exceeds 1460 mA cm(-2) at 1.3 V in SOEC mode. Under H2O/CO2 co-electrolysis at 800 degrees C, the H-2 and CO production rates reach 2.19 and 2.77 mL min(-1) cm(-2) at -708 mA cm(-2) with nearly 100% faradaic efficiency. Moreover, the symmetric cell displays good stability under CO2 and H2O co-electrolysis, indicating that LSFNb oxide is a promising symmetric electrode material for steam and CO2 co-electrolysis as well as for regenerative fuel cells. (C) 2018 The Electrochemical Society.