Distribution of Relaxation Times Analysis for Electrochemical Impedance Spectroscopy in Proton Exchange Membrane Electrolysis Cells

In fuel cells and secondary batteries, ohmic and polarization resistances are commonly separated using electrochemical impedance spectroscopy (EIS).In proton exchange membrane fuel cells, the oxygen reduction reaction is recognized as the rate-determining process, making EIS one of several complementary electrochemical evaluation methods.In contrast, in proton exchange membrane electrolysis cells (PEMECs), both oxygen gas and liquid water diffuse at the oxygen electrode, necessitating the analysis of their respective mass transport processes in addition to the oxygen evolution reaction (OER).In this work, EIS data obtained from a commercially available PEMEC are deconvoluted using distribution of relaxation times (DRT) analysis.Apart from peaks associated with proton transport, hydrogen evolution reaction, and the OER, two distinct peaks are observed at low frequencies below 30 Hz.As the operating voltage increases, the DRT at 1-30 Hz decreases, while that at 0.1-5 Hz increases, suggesting that the peaks ascribe to the oxygen gas diffusion and liquid water transport processes, respectively.At high operating voltages, the enhanced flow of oxygen bubbles exacerbates water transport, highlighting the importance of optimizing the porous transport layer to enhance both oxygen and water transport for improved PEMEC performance.