Application of distribution of relaxation times method in polymer electrolyte membrane water electrolyzer

Distribution function of relaxation times (DRT or DFRT) is a well-established method of solving electrochemical impedance spectroscopy (EIS) data from electrochemical component, such as fuel cells and battery. It can be used to develop the most accurate equivalent circuit models without the input of any circuit architecture information, due to the complexity in equivalent circuit model (ECM). For the first time, this paper implemented DRT methods in polymer electrolyte membrane water electrolyzers (PEMECs). The regularization parameter, characteristic parameters and frequency factors of the solving process are introduced. The results show that (1) DRT method represents the original impedance spectrum of hydrogen production in the form of three characteristic peaks, which correspond to the main polarization processes in hydrogen production system, including water/gas diffusion, hydrogen evolution reaction (HER), oxygen evolution reaction (OER) reactions, and proton transfer processes. (2) The optimal regularization parameter is 0.01 for different current and temperature. (3) The frequency of water/gas diffusion, HER /OER reactions and proton transfer processes is 0.1–60 Hz, 100–1000 Hz and 2000–4000 Hz, respectively. (4) DRT methods couples with genetic algorithm can effectively identify various types of polarization impedance corresponding to different characteristic frequencies without equivalent circuit model.