Investigation on the distribution of dynamic polarization behavior of proton exchange membrane fuel cells based on time resolution electrochemical impedance spectroscopy

Proton Exchange Membrane Fuel Cells (PEMFC) have the potential to serve as the next-generation power source for vehicles. Dynamic operating conditions play a crucial role in influencing the performance and lifespan of PEMFC, highlighting the necessity for in-depth research. Currently, studies primarily rely on monitoring the trends in voltage and current changes, lacking more effective means to explore the internal polarization processes. This paper presents a novel time resolution electrochemical impedance spectroscopy (EIS) measurement approach based on wavelet transforms (WT) and multi-sine excitation. Compared to the short-time Fourier transform (STFT) for time-frequency transform, the method proposed in this study demonstrates enhanced stability of EIS result for dynamic conditions. In this work, the proposed method is employed for the acquisition of time resolution EIS (10-1500 Hz) under step loading and unloading for the first time, and achieves a time resolution up to 0.1 s. By utilizing an equivalent circuit model, various PEMFC parameters are monitored during step-changing current and relaxation processes. Subsequently, combined with distribution testing based on printed circuit board (PCB), it was discovered that the non-uniformity in the rate of oxygen diffusion in various regions after loading is the primary factor leading to the different trends in current changes of them. And the primary reason for oxygen starvation is the obstruction of oxygen transport pathways due to the generated water suddenly. During the relaxation process after step unloading, the periodic changes in the charge transfer resistance (Rct) observed at the air outlet of PEMFC are caused by the drainage issues. This method enhances the research approaches for PEMFC under dynamic operating conditions and is of significant importance for optimizing control strategies.