Experimental Characterization of the Compressive Behaviour of Gas Diffusion Layers in PEM Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells;Gas diffusion layer (GDL);Compression;Compressive stress-strain;Cyclic compression;Mechanical Engineering

Roohparvarzadeh, Sogol

University of Waterloo

关键词: Polymer electrolyte membrane (PEM) fuel cells;    Gas diffusion layer (GDL);    Compression;    Compressive stress-strain;    Cyclic compression;    Mechanical Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/8906/2/Roohparvarzadeh_Sogol.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Successful commercialization of polymer electrolyte membrane (PEM) fuel cells is highlydependant on performance of the membrane electrode assembly (MEA). The performanceof the gas diffusion layer (GDL) of the MEA is highly influenced by applied compressiveload. Compression of the GDL changes its porosity and microstructure, which will conse-quently change the physical properties of the GDL. Hence to improve the properties of theGDL, understanding its compressive behaviour is crucial.In the present study, the compressive behaviour of the GDL is characterized by per-forming a series of compression tests using a compression apparatus. The compressive testis first performed on an untreated carbon paper by measuring its thickness as a function ofcompressive load at room temperature. The obtained results are analyzed and presentedin a compressive stress-strain curve. The compressive stress-strain curve of the GDL isdivided into 3 distinct regions. The first region represents the stress-strain behaviour atvery low stress values. In this region, the compressive strain of the GDL increases rapidlyand linearly with the applied stress. In the second region, the compressive strain increasesless rapidly and non-linearly with applied stress. In the last region, the compressive stress-strain behaviour becomes linear again, but the strain increases at a lower rate. Analysisof the SEM images for both compressed and uncompressed GDL samples suggest thatthe stress-strain behaviour of the GDL in the first two regions is induced by the surfaceroughness and local thickness variations.The compressive behaviour of the GDL is further analyzed by investigating the effect oftemperature, relative humidity, and hydrophobic treatment. The compressive stress-straincurves obtained at temperatures of 25 ◦ C, 45 ◦ C, 65 ◦ C, and 85 ◦ C are almost identical withinthe experimental margin of error, which suggests that fuel cell’s operating temperature hasno appreciable effect on the compressibility of the GDL. The compressive stress-straincurve obtained from compressive test at humidified environment shows a higher changein strain in the second region of the curve. The study on the effect of Polytetrafluo-roethylene (PTFE) coating on compressibility and pore distribution shows that increasein PTFE content decreases the overall pore volume of the GDL and hence decreases thecompressibility.At last, the effect of cyclic loading is studied by measuring the thickness of GDLsamples during 2500 loading/unloading cycles. The strain of the GDL samples increasesby 50% after the samples undergo 2500 cycles of compression. The effect of unloadingwas further investigated by measuring the thickness of the sample as a function of appliedcompressive load while loading the sample by compression pressures of up to 3.5MPa and then unloading the sample to zero MPa for seven cycles. It is found that the structureof the GDL degrades significantly under compression cycles. This study concludes thatthe compressive behaviour of the GDL under cyclic compression is a major drawback andwithout further improvements, the required durability will not be achieved.