This paper reports a series of new electrochemical impedance measurements that were performed on an anode supported planar solid oxide fuel cell (SOFC) tested at different anode gas conditions and at different applied voltages. This study indicates that impedance spectroscopy can resolve four different processes, as long as one of those processes does not become too large. At open circuit voltage the four processes can be resolved best; however, as a voltage is applied the processes are convoluted and cannot be resolved properly. Two of the processes seem to remain almost unchanged as the fuel conditions are changed and can be attributed to the cathode. The two anode processes change with the fuel conditions and both indicate a dependence on charge transfer and diffusion. This methodology can be applied to determine the mode or modes of SOFC degradation for long term testing where one or both electrodes are deteriorating over time.

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