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research-article

Characteristic Time Constants Derived from the Low Frequency Arc of Impedance Spectra of Fuel Cell Stacks

[+] Author and Article Information
Stefan Keller

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
stefan.keller@ise.fraunhofer.de

Tansu Özel

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
tansu.oezel@ise.fraunhofer.de

Anne-Christine Scherzer

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
anne-christine.scherzer@ise.fraunhofer.de

Dietmar Gerteisen

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
dietmar.gerteisen@ise.fraunhofer.de

Ulf Groos

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
ulf.groos@ise.fraunhofer.de

Christopher Hebling

Fraunhofer Institute for Solar Energy Systems ISE, Hydrogen Technologies, Department Fuel Cell Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany
christopher.hebling@ise.fraunhofer.de

Yiannos Manoli

University of Freiburg, Department of Microsystems Engineering – IMTEK, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
ymanoli@imtek.uni-freiburg.de

1Corresponding author.

ASME doi:10.1115/1.4038632 History: Received August 12, 2016; Revised November 13, 2017

Abstract

Electrochemical Impedance Spectroscopy (EIS) is used during operation of different polymer electrolyte membrane fuel cell (PEMFC) stack assemblies at various conditions with special interest given to the characteristic time constant tlow-f derived from the low frequency arc of the spectra which is typically in the range of approx. 15 to 0.5 Hz. This was done by fitting an equivalent electrical circuit (EEC) to the data. Parameter variation performed on a 90 cell stack assembly suggests that conditions leading to different air flow velocities in the flow channels affect tlow-f while other parameters like humidity influence the impedance spectrum, but not tlow-f. Comparison of the stoichiometry variation between short stack and locally resolved single cell shows similar results with the stack´s time constant matching that of the cell´s segments which are located off-center towards the outlet. However, a nonlinear dependency between gas flow velocity and tlow-f especially at low stoichiometric values is obvious. Results from stoichiometry variations at different pressure levels suggest that this could be attributed to the different steady state oxygen partial pressures during the experiments. Comparison of the stoichiometry variation between different stack platforms result in similar dependencies of tlow-f on air flow rate with respect to a reference oxygen partial pressure regardless of size, flow field, geometry or cell count of the stack. The time constant caused by oxygen diffusion through the gas diffusion layer, tGDL was approximated and compared to tlow-f.

Copyright (c) 2017 by ASME
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