Abstract
This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the ‘displacement factor’ are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles.
Highlights
The gas diffusion layer (GDL) plays a crucial role in the operation of polymer electrolyte fuel cells (PEFCs)
The unit comes with a pre-set range for compression up to 2.5 MPa with a resolution of 0.01 MPa based on an active cell area of 6.2 cm2, the bipolar plate flow field features a single serpentine design with land and channel thickness of 1.2 mm and 1.1 mm respectively
The response indicates that after one cycle of compression to a maximum value of 2.5 MPa the gas diffusion layers (GDLs) material exhibits irreversible compression resulting in a deficit between the initial displacement value and the value after the cycle that is 32% of the total displacement change
Summary
The gas diffusion layer (GDL) plays a crucial role in the operation of polymer electrolyte fuel cells (PEFCs). The GDL enables gas to diffuse to and from the electrode surfaces, removes water from the electrode, provides electrical conduction between the current collector (bipolar plate) and the catalyst layer and provides a thermally conductive path to dissipate the heat produced at the catalyst. A significant performance limitation for fuel cells is the ohmic losses associated with contact and bulk resistances. Of these ohmic losses, the contact resistance between the GDL and the land of the flow channels of the bipolar plate plays a significant part. Contact resistances are known to be greatly affected by the compaction force applied and the way the fuel cell is assembled.
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