Abstract: During the operation of proton exchange membrane water electrolysis (PEMWE) stacks, common issues such as metering deviations and pressure abnormalities make the online diagnosis of failures and adaptive control crucial for ensuring stable performance. This study integrates electrochemical impedance spectroscopy (EIS) and total harmonic distortion (THD) analysis to conduct both theoretical simulations and experimental investigations of linear and nonlinear frequency responses in PEMWE single cells, aimed at distinguishing between two types of failure modes. The results indicate that both high feedwater flow and system pressure loss lead to a reduction in the activity of the electrolyzer single cell and an increase in the EIS magnitude across the full frequency range. However, the THD spectra exhibit distinct and discernible frequency-dependent responses: high feedwater flow elevates THD in the 0.1–100 Hz range, whereas pressure loss reduces THD in the low-frequency range of 0.05–1 Hz. The THD spectrum exhibits opposite trends in the characteristic frequency bands, enabling it to differentiate flow-rate deviations from pressure-related failures, in contrast to voltage monitoring and EIS.

Key words: Electrochemical impedance spectroscopy (EIS), Total harmonic distortion (THD), Proton exchange membrane water electrolysis (PEMWE), Fault diagnosis