Impact of cyclic mechanical stress on the electrical contact resistance between gas diffusion layer and bipolar plates in Polymer Electrolyte Membrane Fuel Cells

Abstract : Fuel cell components, Polymer Electrolyte Membrane Fuel Cell Among the various fuel cell technologies, the Low Temperature Proton Exchange Membrane Fuel Cell (LT-PEMFC) is one of the major alternative energy solutions to power vehicles, to supply mobile devices and buildings. These electrochemical devices undergo several internal and external mechanical constraints. The sources of the external constraints are the real life operating conditions (e.g. car vibrations, bumps and collisions) and the mechanical clamping stress applied during the stack assembly. The internal stresses come from the shrinking and the swelling of the membrane caused by water content and the difference between the thermal expansion coefficients of the cell components. These mechanical stresses have an impact on the global fuel cell's performance and one of the most sensitive cell's components to this pressure is the Gas Diffusion Layer (GDL). This layer, assembled with the membrane electrode assembly, provides the reactant gases, evacuates the produced heat and water, and conducts the electrons. GDLs are generally made of a porous media based on carbon fibres. In order to optimise the fuel cell design, the impact of the mechanical stress applied to the GDL on the electrical performance of the fuel cell must be clarified. In this paper, a particular electrical-mechanical relationship is investigated. The electrical contact resistance between the GDL and the bipolar plate , which represents one of the major ohmic losses in the cell is experimentally determined under cyclic compression. This contact resistance is measured using the Transmission Line Measurement (TLM) method, which is applied to the GDL outside of the cell (this method is commonly used to measure semiconductor-metal contact resistances). A cyclic compression from 0 to 8 MPa is applied to the GDL while the electrical resistance is measured. Six types of non-woven GDLs had been studied: Three samples from Sigracet (one untreated, one PTFE treated straight carbon paper GDL, and a similar to the latter coated with a Microporous Layer), two samples from Toray (untreated straight carbon fibre GDLs with different thicknesses) and one specimen from Freudenberg (felt carbon fibre treated with a hydrophobic agent). The experimental results show that the electrical contact resistance decreases rapidly with compression for small stress values (0 - 3MPa), then it becomes more stable. The displacement and the electrical contact resistance of the GDL are sensitive to the cyclic compression effect especially for lower loads (0 - 4MPa). The GDLs from Toray exhibit lower electrical contact resistance compared to the ones from Sigracet. However, the GDLs from Toray were more brittle than the GDLs from Sigracet. The hydrophobic agent increases the mechanical resistance of the GDLs but decreases the electrical contact resistance. The MPL decreases the electrical contact resistance. The GDL from Freudenberg has very close mechanical and electrical behaviour to the MPL coated GDL from Sigracet while having a different structure. The felt fibre GDL shows the best mechanical strength.
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https://hal.utc.fr/hal-01981913
Contributor : Yann Meyer <>
Submitted on : Sunday, February 17, 2019 - 11:14:18 PM
Last modification on : Monday, April 1, 2019 - 12:58:02 PM

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  • HAL Id : hal-01981913, version 1

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Khadidja Bouziane, El Khetabi, Rémy Lachat, Yann Meyer, Denis Candusso, et al.. Impact of cyclic mechanical stress on the electrical contact resistance between gas diffusion layer and bipolar plates in Polymer Electrolyte Membrane Fuel Cells. WHEC 2018 - 22nd edition of the WORLD HYDROGEN ENERGY CONFERENCE, Jun 2018, Rio de Janeiro, Brazil. ⟨hal-01981913⟩

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