This paper proposes the use of electrochemical impedance spectroscopy (EIS) to estimate the cathode flow rate in a fuel cell system. Through experimental testing of an eight-cell, hydrogen-fueled polymer electrolyte stack, it shows that the ac impedance measurements are highly sensitive to the air flow rates at varying current densities. The ac impedance magnitude at 0.1Hz allows the distinction of air flow rates (stoichiometry of 1.5–3.0) at current densities as low as 0.1A/cm2. Using experimental data and regression analysis, a simple algebraic equation that estimates the air flow rate using impedance measurements at a frequency of 0.1Hz is developed. The derivation of this equation is based on the operating cell voltage equation that accounts for all the irreversibilities.

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