Analysis and compensation of PEM fuel cell instabilities in low-frequency EIS measurements

This paper analyzes possible humidity-related instabilities of polymer electrolyte membrane (PEM) fuel cell (FC) operation that affect electrochemical impedance spectroscopy measurements. The compensation of ohmic resistance variations due to such instabilities, achieved using the well known multisine excitation technique with properly chosen high-frequency harmonic components, is proposed here as a new approach to improve low-frequency measurements. Additionally, this method allows a more accurate determination of equivalent circuit parameters identified from impedance spectra and their uncertainties taking into account correlation between impedances at different frequencies, and thus avoiding uncertainty overestimation of low-frequency parameters (such as transport and activation equivalent resistances) that is likely to occur with classic measurement techniques. The proposed method is experimentally validated on a single PEM FC.