DRT-based impedance analysis of two-phase flow conditions in PEM water electrolyzer cells

The accumulation of hydrogen and oxygen within the flow channels of proton exchange membrane water electrolysis cells results in increased gas fractions and pronounced two-phase flow effects at higher current densities. Spatially resolved segmentation along the channel permits investigation of such gradients but necessitates complex hardware. In this study, a simplified method is introduced to emulate local gas production in an incremental cell through controlled injection of well-defined amounts of hydrogen and oxygen into the respective inlet streams. The impact of the gas-to-water ratio on ohmic resistance and polarization phenomena is examined using electrochemical impedance spectroscopy combined with subsequent distribution of relaxation times analysis. This reveals membrane dehydration effects as well as an impact on activation-related losses on the cathode side. A detailed comparison between an incremental (zero gradient) cell and an along-the-channel cell demonstrates a good overall performance correlation. In the medium current density region (2-3 A cm$^{−2}$), the along-the-channel cell shows significantly increased polarization losses, which might be attributed to contamination from ion release from the CCM and/or mass transport issues.