Keywords: EIS PEM fuel cells Hydrogen leak Hydrogen pumping Air starvation Fuzzy logic a b s t r a c t When hydrogen leaks through holes or cracks in membrane-electrode assemblies (MEAs) in Proton Exchange Membrane (PEM) fuel cells, it recombines directly with air. This recombination results in a reduction in oxygen concentration on the cathode side of the MEA. In this paper, the signatures of electrochemical impedance spectroscopy (EIS) are analyzed in different multi-cell stack configurations to show the relation betweenhydrogen leak rate and reduced oxygen concentrations. The reduction in concentration was made by mixing oxygen with nitrogen at different rates, and the increase in hydrogen leak rate was made by controlling the differential pressure (dP) between anode and cathode. To analyze the impedance signatures, we fit the data of oxygen concentration and dP with the parameters of a Randles circuit. The correlation between the parameters of the two data sets allows us to understand the change in impedance signatures with respect to reduction of oxygen in the cathode side. To have a better insight on the effect of insufficient oxygen at the cathode, a model that establishes a relationship between impedance and voltage was considered. Using this model along with the impedance signatures we were able to detect the reduction of oxygen concentrations at the cathode with the help of fuzzy rule-base. However, resolution of detection was reduced with the reduction of leak rate and/or increases in the stack cell count.
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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