Neue Charakterisierungsmethoden für die Gasdiffusionslage in PEM-Brennstoffzellen vor dem Hintergrund produktionsprozessbedingter Materialschwankungen

摘要

Within the scope of the optimization of the gas diffusion layer production process, 12materials were made using the Design of Experiments method. The 12 cathode gas diffusionlayers have the same carbon fiber substrate and only differ in terms of process parametersfor impregnation and micro porous layer coating. During short stack testing at 40°C three ofthe materials unexpectedly lead to a loss of power of over 50 %, although standard ex-situcharacterization showed no significant difference between the 12 materials.The aim of this work was to study the production process induced material variation and todevelop new characterization methods to understand the cause of the power loss. In a firststep an optical high-resolution method was developed which characterizes the gas diffusionlayer roughness under compression as well as the camber of carbon fiber substrate into thechannel and the behavior of irregularities with increasing compression.Afterwards a method for measuring the oxygen transport resistance was validated andapplied on current gas diffusion layers. The results show that this method offers a costefficientway to forecast the performance of fuel cell stacks in normal operating points.Beside the known dry and wet oxygen transport resistance plateaus, an additional state ofunexpected high resistances was found. Further testing by means of kryo-SEM and laserperforation showed the presence of excessive liquid water in the CCM-MPL-interface at lowtemperature operating points. The application of these findings on the initial problem showthat the GDL induced power loss in short stacks at 40°C can be assigned to CCM-MPLinterface flooding, which can be predicted with the method for measuring the oxygentransport resistance.