Study of the mechanical interaction between gas diffusion layers and bipolar plates in low temperature fuel cells

Abstract

In PEFC and DMFC the reaction and product gases and liquids will be transported in the channels of the bipolar plates as well as the gas diffusion layers (GDLs). When optimizing fuel cells each of the components is commonly optimized independently. The interaction of the different fuel cell components is frequently neglected. The function of both, bipolar plates and gas diffusion layers is to distribute and collect gases and liquids on different scales. Therefore the matching and the interaction of both components are important. The DLR has started to investigate these interactions. First, the mechanical effects were investigated, whereby this work was mainly focused on the compression of the gas diffusion layers and the impression of the gas diffusion layer into the flow field channels. The impression of the gas diffusion layers into the flow field channels as a func¬tion of pressure was determined by three different methods: • Optically by inspection with an microscope • Measurement of the pressure drop over the flow field • Electronically by measuring the change of the capacitance upon contact pressure For this purpose the DLR has developed an appropriate measurement instrumentation that consists of a copper plate with spark-eroded channels, ridges of acrylic glass therein and the gas diffusion layer on the ribs. This set-up acts as a parallel connection of different capacities. Accordingly the depth of impression in the gas diffusion layer can be determined by measuring the change of the electrical capacity if the material is pressed in the channel structures. The design of this assembly allows a visual verification by optical microscopy. The total compression of the backing over the ribs can only determined by microscopy.