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The concentration, activation, and total polarizations of the cathode in a cathode-supported solid oxide fuel cell (SOFC) were theoretically and experimentally investigated. In the theoretical analysis, the exchange current density of the charge transfer was considered to be dependent on the PO2 determined by the preceding O2 diffusion, resulting in an interrelationship between activation and concentration polarizations. The established nonlinear polarization equations were then applied to solve the key parameters with area specific resistances and overpotentials of the polarizations experimentally measured by electrochemical impedance spectroscopy on an operating cathode-supported SOFC. To ensure the consistency and meaningfulness of the solutions, the limiting current density in the concentration polarization equation was first solved, followed by the exchange current density of the activation polarization equation using the predetermined limiting current density. The model was finally verified by comparing the directly measured total overpotentials with the calculated ones using the obtained parameters. The agreement between the two favorably supported the proposed cathode polarization model.