Inductive loops in impedance spectra of PEM water electrolyzers

Inductive loops at low frequencies in impedance spectra of proton exchange membrane (PEM) water electrolysis cells remain largely unexplored, yet they hold potential for performance enhancement due to their positive impact on the overall cell resistance. This study investigates inductive loops at low frequencies by impedance spectroscopy and subsequent Distribution of Relaxation Times (DRT) analysis. The positive impact of the inductive loops is verified by voltage current scan measurements. Variations of operational and structural parameters, like membrane and catalyst layer properties and impregnated porous transport layers are performed to understand the origin of the inductive feature and its interplay with mass transport related processes. Our findings reveal a significant impact of current density and voltage, temperature and membrane thickness on the inductive loop. Measurements via reference electrodes show a stronger correlation to the anode. Mass transport losses and the inductive loops are occurring in similar frequency ranges. Such overlapping of both effects with apparently positive and negative resistances can result in compensation in the spectra. The size of the inductive loops, which might even exceed the capacitive polarization resistance, and their dependence on the membrane thickness indicate that processes in the membrane are responsible for the observed behavior.