Finite Element Model Based Determination of Local Membrane Conductivity of Polymer Electrolyte Fuel Cells

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A non-invasive method to determine the local relative humidity (RH) and local high-frequency resistance (HFR) distribution from inlet to outlet of polymer electrolyte fuel cells (PEFCs) is presented. The method uses a plurality of electrodes attached to the outer flow field surface to inject alternating currents and measure the resulting voltage amplitudes at the flow fields’ surface. Because the measured voltage amplitudes are highly dependent on the actual electrode positioning on the flow field boundaries, they are interpreted by interpolation between reference measurements at homogeneous relative humidity conditions and known overall cell impedance. The method is implemented experimentally using alternating current injections at a frequency of 1 kHz at well-defined asymmetric in situ N2/N2 conditions on a 200-cm2 cell in a 6-cell short-stack. The comparison between the RH distribution and the outlet RH sensor data yields a very good match. The same can be said when comparing the HFR distribution and the global cell HFR. Finally, the sensitivity of the method is tested by varying the mass flow rate with asymmetrical RH conditions. The results are highly reproducible in all the tested conditions.

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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

Schuller

Schmidt

Eller

2022

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“…There are however currently no methods able to non-invasively provide local information on the membrane high frequency resistance (HFR): there is always a need for either stack inserts or segmented flow fields. [12][13][14][15][16] In this context, a method inspired from Electrical Impedance Tomography (EIT) 17 is being developed. It relies on boundary voltage measurements on the flow field's outer surface and aims at providing local HFR information.…”

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confidence: 99%

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

Schuller

Schmidt

Eller

2022

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.

“…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.…”

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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.