A Physics-Based Impedance Model of Proton Exchange Membrane Fuel Cells Exhibiting Low-Frequency Inductive Loops

Abstract

A physics-based impedance model of a proton exchange membrane fuel cell is developed, incorporating a coupled oxide growthoxygen reduction reaction kinetic model. The oxide layer is shown to produce a low frequency inductive loop that agrees quantitatively with the experimental inductive loop at current densities as high as 800 mA/cm 2 , even when kinetic and mass-transfer parameters are fit from polarization curves and cyclic voltammetry instead of electrochemical impedance spectroscopy. The importance of the inductive loop in explaining both AC and DC results is discussed. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0361506jes] All rights reserved.Manuscript submitted October 31, 2014; revised manuscript received February 16, 2015. Published March 3, 2015 Electrochemical impedance spectroscopy (EIS) is a widely used technique in proton exchange membrane fuel cells (PEMFCs) that separates differential contributions to cell overpotential by characteristic time constants. Analysis of EIS is difficult because there may be dozens of processes involved. It is standard to analyze EIS using equivalent electrical circuit models of the PEMFC, in which several key processes are represented by circuit elements such as the resistor, capacitor, Warburg element, and constant phase element. Fitting the experimental EIS data with an equivalent circuit model and obtaining circuit parameters is straightforward. Often, a close fit can be achieved with relatively few components, especially when constant phase elements are used. However, the challenge becomes determining which processes to include and converting the electrical circuit parameters back to meaningful cell parameters.Although the basic building blocks of equivalent circuits, for example the Randles circuit, have an exact physical interpretation, these elements are often applied to more complex processes without accounting for the differences. The circuits may fit the data perfectly, but the parameters have lost their original meaning. Often, some transport processes are faster than double layer charging, and as a result, are inseparable from charge-transfer resistance. Additionally, slow transport processes often contribute impedance that scales with chargetransfer resistance, rather than being independent. Unfortunately, it is common in the literature to see circuit parameters reported as results without a translation to meaningful physical parameters.An alternative approach is to model the physical processes occurring in an electrochemical cell during EIS experiments. This approach was pioneered by De Levie, 1 who calculated an analytical solution for the impedance of a porous electrode with a potential gradient, assuming linear kinetics and no concentration gradient. Keddam et al. 2 cons...

Evolution of microstructure and electrochemical corrosion characteristics of cold compacted magnesium

“…The stability of the corrosionprotecting layer was evident on the changed plots which led to using the simplified equivalent circuit. After 12 h of exposure, the corrosion behaviour of the wrought material changed again, an inductive loop was present due to partial damage to the protecting corrosion layer [20].…”

Impact of the Cathode Pt Loading on PEMFC Contamination by Several Airborne Contaminants

“…The high-frequency intercept represents the ohmic resistance, which is mostly caused by the poorly conducting membrane [45]. Multiple explanations were proposed for the inductive impedance values at the lowest and highest frequencies, including electrical cables [46,47] for high frequencies, and processes involving side reactions with intermediate species [47], oxide growth [48], or a slow ionomer water uptake/release [49] for low frequencies. Most of these considerations were either ignored because they did not focus on relevant aspects (electrical cables) or were easily dismissed because, in the absence of contaminants, the cathode potential was too low for Pt oxidation and the sub-saturated air stream did not yield an inductive behavior.…”

Polymer electrolyte membrane fuel cell operating in stoichiometric regime

“…An ubiquitous drawback to all the models reported in the previous references is the large number of parameters required (more than ten in general, see Refs. [10,11] for example). If few of them can be easily obtained such as the cell dimensions, or operating conditions, most parameters related to the GDL properties (conductivity, permeability), catalyst layer properties (kinetic reaction coefficients) or PEM properties (drag coefficient [12], ionic conductivity) arein most casesnot accurately known, which introduce a lot of uncertainty in fuel cell model results.…”