The results of electrochemical impedance spectroscopy of PEM fuel cells may exhibit inductance at low frequencies. A standard representation of fuel cell processes by equivalent circuit models involving resistance/capacitance loops representing activation losses on both anode and cathode in series with a resistance, cannot explain inductance at low frequencies. A novel equivalent circuit model is made by adding additional resonance loops comprising of a resistance, capacitance and inductance, for both anode and cathode, representing mass transport and resistive losses within the catalyst layer. The model was used to fit the results of an accelerated stress test. The results indicate that resistance, capacitance and inductance representing the cathode catalyst layer change dramatically during the accelerated stress test, and this shows good agreement with the findings of the periodic diagnostic tests.
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