Tunable diode laser absorption spectroscopy (TDLAS) is used to measure the local ac response of the water partial pressure to a sinusoidal current excitation during locally resolved impedance measurements in a sub-saturated polymer electrolyte fuel cell (PEFC). The experimental results, along with the locally resolved impedance data are compared to calculated data as obtained from a 1+1 dimensional ac impedance model. The detailed experimental data allows model validation and in situ parameter determination. The model results are in good agreement with the experimental results. This emphasizes the importance to consider the build-up of water partial pressure oscillations along the gas channels in ac impedance models for sub-saturated PEFCs. The results show that minor modifications of literature membrane parameters are needed for a good fit to the experimental data set.

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