A new performance study has been performed on a commercially available anode supported planar SOFC containing an LSCF cathode. The SOFC cell is tested at different temperatures and different cathode gas compositions. The temperature and cathode gas dependence on the electrochemical performance is studied using voltage current density curves and impedance spectroscopy at different cell voltages. The cell tested shows excellent performance at all temperatures and is not limited by diffusion losses for the tested conditions. This new study indicates that the cell impedance spectroscopy is comprised of at least four semicircles of which two are partially dependent on the cathode gas conditions. It was found that historical effects play a role in the impedance spectra, showing some scatter in the ohmic resistance as a function of applied voltage. The cell ohmic resistance decreases as the temperature increases and as the cathode gas conditions are switched from air to O(2)-He mixture. However, the cell ohmic resistance under pure O(2) was found to be higher than the O(2)-He mixture. In virtually all IS data, the cell ohmic resistance showed a maximum value around 0.8 V. The cell ohmic ASR shows that interfacial resistances are a significant portion of the total ohmic resistance. The total electrode polarization decreases as the temperature increases and as the cathode gas conditions are switched from air to O(2)-He mixture and to pure O(2). Finally, the peak frequency of the largest semicircle observed at high frequency shows a linear dependence on the applied voltage in most cases. This behavior is related to the charge transfer that occurs in the high frequency range and indicates that the electrochemical reactions are occurring at faster rates as more current flows through the cell. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.