BaZr1-xCoxO3-delta(BZC-x, x = 0.1, 0.2, 0.3, 0.4, 0.5) are prepared and identified as single phase air electrode materials for reversible solid oxide cells. BZC-x shows a typical perovskite structure with x <= 0.4, and slight BaCoO3 second phase is observed with x = 0.5. Conductivity measurements suggest that BZC-x is an oxygen ion and electron mixed conductor in dry oxygen atmosphere. The electronic conductivity of BZC-x increases when increasing Co content in BZC-x specimen, while the ionic conductivity reduces. For BaZr0.6Co0.4O3-delta, the electronic and ionic conductivity are 5.24 S cm(-1) and 1.20 x 10(-3) S cm(-1), respectively, measured at 700 degrees C in dry oxygen. With BZC-0.4 as a single phase air electrode, the discharging and electrolysis current densities of a single cell are 299 mA cm(-2) (at 0.7 V) and -935 mA cm(-2) (at 1.5 V), respectively, measured at 700 degrees C. The polarization resistance of cells using this new air electrode is only 0.19 Omega cm(2), approximately 65% lower than that using a traditional Sm0.5Sr0.5CoO3-delta/BaCe0.5Zr0.3Y0.2O3-delta composite air electrode. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.