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Electrochemical pressure impedance spectroscopy (EPIS) analyzes the voltage response of a polymer electrolyte fuel cell (PEFC) as a function of an applied pressure signal in the frequency domain. EPIS is similar to electrochemical impedance spectroscopy and its development was inspired by the diagnostic capabilities of the latter. The EPIS introduced in this work modulates the cathode pressure of a PEFC with a sinusoidal signal through the use of a back-pressure controller, and monitors the cell voltage while holding the cell at a constant current. A sinusoidal pressure wave propagates along the flow field channels because of this pressure modulation. This pressure wave impacts local reaction rates and transport properties in the cathode, resulting in a sinusoidal voltage response. The amplitude ratio and phase difference between these two sinusoidal waves entail diagnostic information on processes that take place within the PEFC. To demonstrate the utility of the EPIS technique, experiments have been carried out to measure and analyze the frequency response of PEFCs with two different flow fields. A parametric study has been conducted to characterize the effect of pressure oscillation amplitude, load, oxygen concentration, oxygen stoichiometry and cathode gas flow rate on the EPIS signal.

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h i g h l i g h t sIn-situ diagnostic tool to quantify hydrogen transfer leaks in PEM fuel cell stacks. Closed form relationship for the rate of hydrogen transfer leak. Requires hydrogen/nitrogen supply to anode/cathode with anode overpressure. Requires pressure, flow, temperature, humidity, and OCV measurements. Accurately estimates leak in each cell of a stack, suitable for R&D applications. a b s t r a c tThis paper describes a diagnostic tool for in-situ characterization of hydrogen transfer leak in individual cells of a Polymer Electrolyte Membrane (PEM) fuel cell stack, suitable for Research and Development (R&D) applications. The technique is based on supplying hydrogen and nitrogen to the anode and cathode of a PEM fuel cell stack while maintaining a prescribed anode overpressure. Under these conditions, hydrogen crosses over from the anode to the cathode, and the Open Circuit Voltage (OCV) represents the ratio of hydrogen partial pressure in the two electrodes. It is shown that by measuring temperature, pressure, flow, humidity, and individual OCVs, the proposed technique can accurately estimate the rate of hydrogen transfer leak in individual cells of a PEM fuel cell stack. This diagnostic tool is suitable for characterizing hydrogen transfer leaks during fuel cell R&D, as it only requires gasses and measurements that are readily available on fuel cell test stations, and does not need disassembling or modifying the fuel cell stack.

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