In-situ impedance diagnosis experiment and equivalent circuit modeling based on distribution of relaxation time method for unitized regenerative proton exchange membrane fuel cells

The Distribution of Relaxation Times (DRT) method provides a powerful approach for analyzing Electrochemical Impedance Spectroscopy (EIS) in electronic components, enabling clear separation of different impedance types and accurate equivalent circuit modeling. In this study, the DRT method was applied to unitized regenerative proton exchange membrane fuel cells (UR-PEMFCs) for the first time, establishing an impedance quantification model for in-situ diagnostics of multiple impedances. This foundational framework supports future durability testing efforts. In-situ impedance diagnostics were conducted in both Fuel Cell (FC) and Electrolytic Cell (EC) modes using a custom mode-switching platform. Results show that under constant electrode conditions, the bifunctional membrane electrode enhances round-trip efficiency by 15.75% compared to the constant gas mode. Through DRT imaging in FC and EC modes, impedance information corresponding to distinct relaxation peaks was extracted and assigned based on operational experiments. The three main peaks identified in both modes were attributed to proton transfer impedance, charge transfer impedance, and mass transfer impedance. Additionally, variations in operating conditions led to the appearance of new transport mechanisms within the charge transfer impedance. In FC mode, the DRT-based equivalent circuit model achieved precise fitting. Applying DRT to UR-PEMFCs improves water and bubble management, offering efficient optimization pathways and valuable guidance for cell design, operational parameter refinement, and durability monitoring.