Spatial mapping of cathode CL/PEM oxygen concentration in a large-format PEMFC using an instrumented membrane electrode assembly (iMEA)

This study applies an instrumented membrane electrode assembly (iMEA) approach to enable multi-location, in-plane mapping of oxygen concentration at the cathode catalyst layer/proton exchange membrane (CL/PEM) interface in a 250 cm 2 PEM fuel cell. Three sensors positioned at 63, 163, and 203 mm from the cathode inlet were used to evaluate local oxygen concentration under controlled inlet oxygen concentration steps and air stoichiometry sweeps. Sensor calibration was based on an extended oxygen flux-interrupt approach combined with simultaneous DC current and high-frequency impedance measurements, and a Gaussian Process Regression model was applied to correct for extraneous effects of temperature and humidity to determine oxygen concentration. For all sensors, the measured oxygen concentration decreased with decreasing air stoichiometry and with increasing distance from the cathode inlet. The upstream sensor consistently recorded the highest oxygen concentration, while the downstream sensor showed the lowest values, confirming an oxygen gradient along the cathode flow direction. At the lowest stoichiometry, the most downstream location approached complete oxygen depletion, while the cell voltage remained within a range that could still appear acceptable. These results demonstrate the capability of the developed approach for operando, in-plane mapping of oxygen concentration at the cathode CL/PEM interface.