On the origin of low-frequency inductive loops in the impedance spectra of proton exchange membrane water electrolyzers

Electrochemical impedance spectroscopy (EIS) of proton exchange membrane water electrolysis (PEMWE) cells often reveals low-frequency inductive loops, the origin of which remains debated. This study demonstrates that these features primarily arise from transient thermal effects rather than kinetic or mass transport limitations. A simplified thermal-electrochemical model was developed to simulate thermal dynamics in individual cell components, including the catalyst-coated membrane (CCM), porous transport layers (PTLs), flow fields, and end plates, each treated as a distinct thermal mass. The model reproduces the experimentally observed inductive loops, linking the first loop to rapid CCM and PTL temperature changes and slower loops to thermal transients in the flow field and end plates. Even under thermal steady-state conditions, a sinusoidal current perturbation induces oscillatory heat flux and a slow phase-lagged CCM temperature response, giving rise to low-frequency inductive features. The study further shows how current density, membrane thickness, operating temperature, water flow rate, and boundary conditions influence inductive behavior by affecting heat generation and dissipation. This approach provides a framework for understanding and interpreting low-frequency inductive impedance features, offering a valuable tool for estimating heat transfer coefficients in flow channels and internal CCM temperatures in PEMWE stacks. • Thermal-electrochemical model development to simulate PEMWE EIS spectra. • Low-frequency inductive loops are caused by slow dynamic temperature changes. • The model reproduces the experimental low-frequency inductive impedance features. • Inductive loops are determined by the thermal characteristics of cell components.