Further Understanding of Uncertainties in the Impedance Spectrum of the Polymer Electrolyte Fuel Cell due to Inductive Effects and Oxygen Diffusion Time Constant

Abstract

In this study, uncertainties during the assessment of the electrochemical impedance spectrum of the polymer electrolyte fuel cell (PEFC) attributed to inductive artefacts at high frequencies and inductive loops at low frequencies as well as oxygen diffusion time constant are discussed. A validated impedance model represented as an equivalent electrical circuit of a PEFC allowed the simulation of the effect of inductive artefacts, inductive loops and oxygen diffusion time constant on electrochemical impedance spectroscopy (EIS) measurements represented in the Nyquist plot. This study considers EIS measurements reported in previous studies and provides an insight into the EIS measurements with positive imaginary components at high frequencies attributed to the intrinsic inductance of the measurement cables during EIS tests and at low frequencies attributed to electrochemical mechanisms (e.g. side reactions with intermediate species) during PEFC operation. In addition, an overview of overlapping mechanisms (charge transfer and oxygen transport resistances during the oxygen reduction reaction) on the PEFC impedance spectrum attributed to oxygen diffusion across the cathode catalyst layer is presented. EIS measurements with positive imaginary components and with overlapping effects could yield to ambiguities when studying or relating electrochemical mechanisms (ion conduction, capacitance, charge transfer and mass transport resistances) of the PEFC through a defined single frequency or a single measured value represented in the Nyquist complex-impedance plot.

Low frequency inductive loop in EIS measurements of an open-cathode polymer electrolyte fuel cell stack. Impedance of water vapour diffusion in the cathode catalyst layer

“…1. In a previous study [60], it was demonstrated that inductive loops shrink the impedance spectrum where the negative imaginary component -Z'' intercepts the real component Z' at low frequencies. EIS measurements in PEFCs [45,61].…”

Parasitic Effects in Impedance Spectrum of PEM Water Electrolysis Cells: Case Study of High‐Frequency Inductive Effects

“…But when stronger inductor component exists, it has to be considered in ECM modeling. [15] Klotz and Shin reported that in the high-frequency range (>1 kHz) certain inaccuracies may occur due to the wiring inductivities. [13,16] Similar effects coming from the instrument setup (potentiostat/power supply internal components, i.e., cables, voltage, and current amplifiers) were also discussed by Erinmwingbovo et al, in a study on instrument artifacts on EIS.…”