Impedance analysis of alkaline water electrolysis based on distribution of relaxation time

Abstract

Electrochemical Impedance Spectroscopy (EIS) is an important tool for identifying electrochemical processes and evaluating electrolyzer performance. Fitting EIS data with equivalent circuits often requires prior knowledge and involves inherent uncertainties. This work performed the experimental measurements of visualized zero-gap water electrolyzer equipped with four different flow channels, and then explored an efficient impedance analysis procedure for Alkaline Water Electrolysis (AWE) coupling with the Distribution Relaxation Time (DRT) method. By determining the optimal regularization parameter λ, typical characteristic peaks were identified corresponding to ion transfer, charge transfer, and mass transfer impedance, respectively. The flow channel structure significantly impacted two-phase flow distribution, with the pin-type channel showing a more uniform flow. Based on the optimal pin-type flow channel structure, the influences of operating parameters (current density, flow rate, and temperature) on the electrolysis performance were experimentally measured, and the impact mechanism was disclosed using the DRT method. The results illustrate that the charge transfer impedance Rt is greatly associated with current density and ohmic resistance RO is highly dependent on flow rate and temperature. At high current densities, the bubble coverage plays an indispensable role in the mass transfer impedance process. This work offers a quantitative method to characterize the AWE performance, which can be employed to optimize the structure and operating parameters of electrolyzers.