Non-Invasive Measurement of Humidity Distribution in Polymer Electrolyte Fuel Cells (PEFCs): Part I. In Situ Proof of Concept

Self Cite

In the second part of the paper series on a noninvasive method to determine the local high frequency resistance (HFR) distribution in polymer electrolyte fuel cells (PEFC), the method is applied to an operating PEFC stack. While in the first part of this paper series the approach of using multiple surface attached electrodes to locally inject 1 kHz AC currents into a cell and to measure the resulting voltage amplitudes at the flow field’s surface was introduced. Its sensitivity was assessed using a stack fed only by nitrogen at different humidification levels. Here, it is confirmed that the approach works also during electrochemical operation. First, the method’s spatial resolution is further explored and improved by using multiple stimulation patterns after examining the local sensitivity of the different electrode combinations to changes in membrane conductivity by finite element model simulations of the current injection. The method is then applied to a stack operated at different current densities, inlet humidities and gas flow configurations. The HFR distributions are in good agreement with literature data and compare well with the global cell HFR. Finally, the method’s transient capabilities are highlighted by measuring the HFR distribution during a current jump and cell drying.

“…Experimental setup.-The experimental setup is the same as described in detail in the first part of this paper series. 18 It includes the following components:…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Fuel cell operating conditions.-The protocol for the reference measurements is the same as described in Ref. 18. It includes 9 RH steps held for one hour from 47% to 98% RH.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Noninvasive Measurement of Humidity Distribution in Polymer Electrolyte Fuel Cells (PEFCs). Part II: Operando Analysis of a Fuel Cell Stack

Schuller

Schmidt

Eller

2022

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“…Similary, Schuller et al used a novel, non-invasive method based on electrical impedance tomography to determine the stationary humidity distribution in their fuel cell stack. 17,18 To the knowledge of the authors, Lai et al were the first who linked the 1 kHz resistance to the membrane water content λ to observe spatial and temporal humidity evolution. 19 They used a segmented 50 cm 2 single cell in co-flow configuration.…”

mentioning

confidence: 99%

An Experimental Study of Humidity Distribution Dynamics in a Segmented PEM Fuel Cell

Schmitt¹,

Bligny²,

Maranzana³

et al. 2022

An approach for local and transient in operando measurements of humidification along the channel of a segmented Proton exchange membrane fuel cell (PEMFC) is presented. Based on the impedances at fixed frequencies and temperature, equivalent relative humidity data is acquired and compared for steady state and transient experiments. Based on our results we can show that the classical 1kHz resistance in combination with a proper parametrization is a good choice for monitoring the ionomer humidification. A fast acquisition rate offers high resolution insights into the spatio-temporal dynamics of a PEMFC. It reveals that the current density and humidity distribution response to changes in stoichiometry and total current is highly inhomogeneous along the channel. The data is further used to establish a qualitative model that explains and predicts local dynamic phenomena occuring along the channel during local drainage or humidification.

Non-Invasive Measurement of Impedance Spectra Distribution in Polymer Electrolyte Fuel Cells

Schuller,

Schmidt,

Eller

2024

Self Cite

Localized measurement of the impedance distribution in an operating polymer electrolyte fuel cell stack is of great importance in providing information on its state of health and performance. However, the current methods’ invasiveness is a brake to a more widespread utilization. This work presents a non-invasive way to measure and interpret local impedance spectra. It is based on local AC current supply and local voltage measurements performed all around the cell via conductive pins contacting the outer surface of the flow fields. The different local spectra are measured on a single cell within a 200 cm2 six-cell stack under different operation conditions and compared to a reference case with homogeneous current density. A simple equivalent electrical circuit is used to fit the impedance spectra and to extract membrane and charge transfer resistance. The variations of these two values are analyzed at five different positions along the channel for different cathode stoichiometries and gas flow configurations.